2024/10/07 更新

写真a

コダマ タツヤ
兒玉 竜也
KODAMA Tatsuya
所属
教育研究院 自然科学系 生産デザイン工学系列 教授
自然科学研究科 材料生産システム専攻 教授
工学部 工学科 教授
職名
教授
外部リンク

学位

  • 博士(理学) ( 1994年3月   東京工業大学 )

研究キーワード

  • Inorganic Material

  • 太陽熱化学

  • Catalyst

  • 触媒

  • 無機材料

  • 水素エネルギー

  • 資源利用化学

  • Energy Science

研究分野

  • ナノテク・材料 / エネルギー化学

  • ナノテク・材料 / 機能物性化学

  • ナノテク・材料 / 無機物質、無機材料化学

経歴(researchmap)

  • 新潟大学   工学部 工学科 化学システム工学プログラム   教授

    2003年4月 - 現在

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    国名:日本国

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  • 新潟大学   工学部 化学システム工学科   助教授

    1997年 - 2003年

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    国名:日本国

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  • 新潟大学   工学部 化学システム工学科   助手

    1995年4月 - 1997年3月

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    国名:日本国

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  • 日本学術振興会 特別研究員

    1992年4月 - 1995年3月

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経歴

  • 新潟大学   工学部 工学科   教授

    2017年4月 - 現在

  • 新潟大学   自然科学研究科 材料生産システム専攻   教授

    2004年4月 - 現在

  • 新潟大学   自然科学研究科 材料生産システム専攻   教授

    2004年4月 - 現在

  • 新潟大学   化学システム工学科   教授

    2003年4月 - 2017年3月

  • 新潟大学   工学部   助教授

    1997年4月 - 2003年3月

  • 新潟大学   工学部   助手

    1995年4月 - 1997年3月

▶ 全件表示

学歴

  • 東京工業大学   大学院理工学研究科博士後期課程   化学専攻

    1992年4月 - 1994年3月

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    国名: 日本国

    備考: 早期修了

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  • 東京工業大学   大学院理工学研究科博士前期課程   化学専攻

    1990年4月 - 1992年3月

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    国名: 日本国

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  • 東京工業大学   理学部   化学科

    1986年4月 - 1990年3月

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    国名: 日本国

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所属学協会

委員歴

  • 日本エネルギー学会   理事  

    2003年   

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    団体区分:学協会

    日本エネルギー学会

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  • 日本太陽エネルギー学会   太陽熱部会 幹事  

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論文

  • Transition metals doped effects for the crystal stabilization of the cerium oxides with the first principle calculation 査読

    Takaki Nishimura, Tatsuya Kodama, Sakane Genta, Tomohiko Ishii

    Scientific Reports   12 ( 1 )   2022年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Springer Science and Business Media LLC  

    Abstract

    In recent years, hydrogen energy has been attracting attention, and the hydrogen gas production using solar thermal energy has been conducted. The studies of Kodama et al. were reported that the cyclic reaction can efficiently produce the hydrogen gas through a two-step thermal redox reaction with the cerium oxide. The transition metal doping into the cerium oxide improved the reaction efficiency. We considered the doping effect on the thermal two-step redox reaction. As a result of the calculation by the DV-Xα method, it was clarified that the doped cerium oxide becomes a strong bond, the large BOP value without changing the ceria crystal structure in the two-step thermal redox reaction. The theoretical calculation results corresponded to the reaction efficiency improvement of the thermal reaction in experimental results.

    DOI: 10.1038/s41598-022-14180-3

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    その他リンク: https://www.nature.com/articles/s41598-022-14180-3

  • Hydrogen production by solar fluidized bed reactor using ceria: Euler-Lagrange modelling of gas-solid flow to optimize the internally circulating fluidized bed 査読

    Selvan BELLAN, Tatsuya KODAMA, Hyun SEOK CHO, Jin-Soo KIM

    Journal of Thermal Science and Technology   17 ( 2 )   22 - 00076   2022年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japan Society of Mechanical Engineers  

    DOI: 10.1299/jtst.22-00076

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  • Development of Synthesis and Fabrication Process for Mn-CeO2 Foam via Two-Step Water-Splitting Cycle Hydrogen Production 査読

    Hyun-Seok Cho, Tatsuya Kodama, Nobuyuki Gokon, Selvan Bellan, Jong-Kyu Kim

    Energies   14 ( 21 )   6919 - 6919   2021年10月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:MDPI AG  

    The effects of doping manganese ions into a cerium oxide lattice for a thermochemical two-step water-splitting cycle to produce oxygen and hydrogen and new synthesis methods were experimentally investigated. In order to comparison of oxygen/hydrogen producing performance, pristine CeO2, a coprecipitation method for Mn-CeO2, and a direct depositing method for Mn-CeO2 with different particle sizes (50~75, 100–212, over 212 μm) and doping extents (0, 5, 15 mol%) were tested in the context of synthesis and fabrication processes of reactive metal oxide coated ceramic foam devices. Sample powders were coated onto zirconia (magnesium partially stabilized zirconia oxide, MPSZ) porous foam at 30 weight percent using spin coating or a direct depositing method, tested using a solar reactor at 1400 °C as a thermal reduction step and at 1200 °C as a water decomposition step for five repeated cycles. The sample foam devices were irradiated using a 3-kWth sun-simulator, and all reactive foam devices recorded successful oxygen/hydrogen production using the two-step water-splitting cycles. Among the seven sample devices, the 5 mol% Mn-CeO2 foam device, that synthesized using the coprecipitation method, showed the greatest hydrogen production. The newly suggested direct depositing method, with its contemporaneous synthesis and coating of the Mn-CeO2 foam device, showed successful oxygen/hydrogen production with a reduction in the manufacturing time and reactants, which was lossless compared to conventional spin coating processes. However, proposed direct depositing method still needs further investigation to improve its stability and long-term device durability.

    DOI: 10.3390/en14216919

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  • Heat transfer and particulate flow analysis of a 30 kW directly irradiated solar fluidized bed reactor for thermochemical cycling 査読

    Selvan Bellan, Tatsuya Kodama, Koji Matsubara, Nobuyuki Gokon, Hyun Seok Cho, Kousuke Inoue

    Chemical Engineering Science   203   511 - 525   2019年8月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    To perform thermochemical cycles using non-volatile metal oxides to split water and produce hydrogen, a directly irradiated fluidized bed reactor is designed and fabricated for beam-down configuration. As the main aim of this investigation is to analyze the heat transfer and particulate flow of the reactor, chemically inert particles are used. A transient 3D heat and mass transfer model is formulated by the combined approach of discrete element method and computational fluid dynamics. The radiative transfer is solved using the discrete ordinate radiation model. Experimental validation is accomplished by the measured temperatures, obtained with the fluidized bed reactor prototype tested under 30 kW high-flux solar simulator. The model is applied to analyze the granular flow characteristics and efficiency of the reactor for various superficial gas velocities and bed masses. The results indicate that higher gas flow rate increases the velocity and convection loss of the bed and decreases the bed temperature and efficiency of the reactor. th

    DOI: 10.1016/j.ces.2018.09.012

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  • Particles fluidized bed receiver/reactor with a beam-down solar concentrating optics: First performance test on two-step water splitting with ceria using a Miyazaki solar concentrating system 査読

    Tatsuya Kodama, Hyun Seok Cho, Kouske Inoue, Tatsuya Saito, Shouta Watanabe, Nobuyuki Gokon, Selvan Bellan

    AIP Conference Proceedings   2126   180011   2019年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AIP Publishing  

    DOI: 10.1063/1.5117691

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  • Heat transfer analysis of 5kW<inf>th</inf> circulating fluidized bed reactor for solar gasification using concentrated Xe light radiation 査読

    Selvan Bellan, Nobuyuki Gokon, Koji Matsubara, Hyun Seok Cho, Tatsuya Kodama

    Energy   160   245 - 256   2018年10月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    A combined numerical and experimental investigation of hydrodynamics and heat transfer of internally circulating fluidized bed reactor for solar gasification of coal coke to produce syngas is reported. As the main objective of this study is to study the thermal performance of the reactor, chemically inert quartz particles have been used. A numerical model has been developed by the combined approach of computational fluid dynamics and discrete element method (CFD-DEM). The radiation transfer equation has been solved by the discrete ordinate (DO) model. The experimental data have been used for model validation. The thermal performance of the reactor and the spout-annulus flow have been predicted by the model and other hydrodynamic parameters such as internal solid volume fraction, velocity and temperature of the particles are analyzed as a function of superficial gas velocity (gas flow rate) at different initial conditions.

    DOI: 10.1016/j.energy.2018.06.212

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  • Particle reactors for solar thermochemical processes 査読

    Tatsuya Kodama, Selvan Bellan, Nobuyuki Gokon, Hyun Seok Cho

    SOLAR ENERGY   156   113 - 132   2017年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Utilization of solar thermal power for high temperature fuel production has the potential to significantly reduce the fossil fuel dependence of our current economy. Over the past two decades, remarkable progress has been made in the development of solar driven thermochemical reactors for the production of hydrogen and syngas as they are promising energy carriers for transportation, domestic and industrial applications. However, there are solar peculiarities in comparison to conventional thermochemical processes high thermal flux density and frequent thermal transients because of the fluctuating insolation-, and conventional industrial thermochemical reactors are generally not suitable for solar driven reactors. Therefore, solar-specific modifications of reactor design are necessary to realize efficient solar driven thermochemical processes. In solar thermochemical reactors, the methods for solar-heating particulate solid feedstock to high temperatures can be broadly classified as solar "directly" and "indirectly" absorbing reactors. On solar thermochemical processes involving reacting solid particles at high temperatures, such as "solar two-step water splitting with metal oxides" and "solar gasification", various types of solar directly and indirectly absorbing particle reactors have been developed. In this review, recent development of solar particle reactors for the above solar thermochemical processes is described. (C) 2017 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.solener.2017.05.084

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  • Thermochemical reactivity of 5-15 mol% Fe, Co, Ni, Mn-doped cerium oxides in two-step water-splitting cycle for solar hydrogen production 査読

    Nobuyuki Gokon, Toshinori Suda, Tatsuya Kodama

    THERMOCHIMICA ACTA   617 ( 10 )   179 - 190   2015年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The thermochemical two-step water-splitting cycle using transition element-doped cerium oxide (M CeO2-delta; M=Fe, Co, Ni, Mn) powders was studied for hydrogen production from water. The oxygen/hydrogen productivity and repeatability of M CeO2-delta materials with M doping contents in the 5-15 mol% range were examined using a thermal reduction (TR) temperature of 1500 degrees C and water decomposition (WD) temperatures in the 800-1150 degrees C range. The temperature, steam partial pressure, and steam flow rate in the WD step had an impact on the hydrogen productivity and production rate. 5 mol% Fe- and Co-doped CeO2-delta enhances hydrogen productivity by up to 25% on average compared to undoped CeO2, and shows stable repeatability of stoichiometric oxygen and hydrogen production for the cyclic thermochemical two-step water-splitting reaction. In addition, 5 mol% Mn-doped CeO2-delta, 10 and 15 mol% Fe- and Mn-doped CeO2-delta show near stoichiometric reactivities. (C) 2015 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.tca.2015.08.036

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  • Simulation of Flux Distributions on the Foam Absorber with Solar Reactor for Thermo-chemical Two-step Water Splitting H2 Production Cycle by the 45 kWth KIER Solar Furnace 査読

    H.S. Cho, N. Gokon, T. Kodama, Y.H. Kang, J.K. Kim

    Energy Procedia   69   790 - 801   2015年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.egypro.2015.03.088

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  • Improved operation of solar reactor for two-step water-splitting H 2 production by ceria-coated ceramic foam device 査読

    H.S. Cho, N. Gokon, T. Kodama, Y.H. Kang, H.J. Lee

    International Journal of Hydrogen Energy   40 ( 1 )   114 - 124   2015年1月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.ijhydene.2014.10.084

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  • Thermochemical two-step water splitting by internally circulating fluidized bed of NiFe2O4 particles: Successive reaction of thermal-reduction and water-decomposition steps 査読

    Nobuyuki Gokon, Tetsuro Mataga, Nobuyuki Kondo, Tatsuya Kodama

    International Journal of Hydrogen Energy   36 ( 8 )   4757 - 4767   2011年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Thermochemical two-step water splitting using a redox system of iron-based oxides or ferrites is a promising process for producing hydrogen without CO 2 emission by the use of high-temperature solar heat as an energy source and water as a chemical source. In this study, thermochemical hydrogen production by two-step water splitting was demonstrated on a laboratory scale by using a single reactor of an internally circulating fluidized bed. This involved the successive reactions of thermal-reduction (T-R) and water-decomposition (W-D). The internally circulating fluidized bed was exposed to simulated solar light from Xe lamps with an input power of 2.4-2.6 kW th for the T-R step and 1.6-1.7 kWth for the subsequent W-D step. The feed gas was switched from an inert gas (N2) in the T-R step to a gas mixture of N2 and steam in the W-D step. NiFe 2O4/m-ZrO2 and unsupported NiFe 2O4 particles were tested as a fluidized bed of reacting particles, and the production rate and productivity of hydrogen and the reactivity of reacting particles were examined. © 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2011.01.076

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  • Ferrite/zirconia-coated foam device prepared by spin coating for solar demonstration of thermochemical water-splitting 査読

    Nobuyuki Gokon, Tatsuya Kodama, Nobuki Imaizumi, Jun Umeda, Taebeom Seo

    International Journal of Hydrogen Energy   36 ( 3 )   2014 - 2028   2011年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    A Ferrite/zirconia foam device in which reticulated ceramic foam was coated with zirconia-supported Fe3O4 or NiFe2O 4 as a reactive material was prepared by a spin-coating method. The spin-coating method can shorten the preparation period and reduce the coating process as compared to the previous wash-coating method. The foam devices were examined for hydrogen productivity and cyclic reactivity in thermochemical two-step water-splitting. The reactivity of these foam devices were studied for the thermal reduction of ferrite on a laboratory scale using a sun simulator to simulate concentrated solar radiation, while the thermally reduced foam devices were reacted with steam in another quartz reactor under homogeneous heating in an infrared furnace. The most reactive foam device, NiFe2O 4/m-ZrO2/MPSZ, was tested for successive two-step water-splitting in a windowed single reactor using solar-simulated Xe-beam irradiation with a power input of 0.4-0.7 kWth. The production of hydrogen continued successfully in the 20 cycles that were demonstrated using the NiFe2O4/m-ZrO2/MPSZ foam device. The NiFe2O4/m-ZrO2/MPSZ foam device produced hydrogen at a rate of 1.1-4.6 cm3 per gram of device through 20 cycles and reached a maximum ferrite conversion of 60%. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2010.11.034

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  • Comparative study of the activity of nickel ferrites for solar hydrogen production by two-step thermochemical cycles 査読

    Fernando Fresno, Tomoaki Yoshida, Nobuyuki Gokon, Rocío Fernández-Saavedra, Tatsuya Kodama

    International Journal of Hydrogen Energy   35 ( 16 )   8503 - 8510   2010年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    In this work, we compare the activity of unsupported and monoclinic zirconia - supported nickel ferrites, calcined at two different temperatures, for solar hydrogen production by two-step water-splitting thermochemical cycles at low thermal reduction temperature. Commercial nickel ferrite, both as-received and calcined in the laboratory, as well as laboratory made supported NiFe2O4, are employed for this purpose. The samples leading to higher hydrogen yields, averaged over three cycles, are those calcined at 700 °C in each group (supported and unsupported) of materials. The comparison of the two groups shows that higher chemical yields are obtained with the supported ferrites due to better utilisation of the active material. Therefore, the highest activity is obtained with ZrO2-supported NiFe2O4 calcined at 700 °C. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2010.05.032

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  • A reactive Fe-YSZ coated foam device for solar two-step water splitting 査読

    Tatsuya Kodama, Tomoki Hasegawa, Ayumi Nagasaki, Nobuyuki Gokon

    Journal of Solar Energy Engineering, Transactions of the ASME   131 ( 2 )   0210081 - 0210087   2009年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    A thermochemical two-step water-splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting solar energy into clean hydrogen in sunbelt regions. An iron-containing yttrium-stabilized zirconia (YSZ) or Fe- YSZ is a promising working redox material for the two-step water-splitting cycle. Fe2+.-YSZ is formed by a high-temperature reaction between YSZ and Fe3O4 supportedon the YSZ at 1400°C in an inert atmosphere. Fe2+-YSZ reacts with steam and generates hydrogen at 1000-1100°C to form Fe3+-YSZ that is reactivated by thermal reduction in a separate step at temperatures above 1400°C under an inert atmosphere. In the present study, ceramic foam coated with Fe-YSZ particles is examined as the thermochemicalwater-splitting device to be used in a solar directly irradiated receiver/reactor system. The Fe-YSZ particles were coated on an Mg-partially stabilized zirconia foam disk, and the foam device was tested during the two-step water-splitting cycle
    this was performed alternately at temperatures between 1100°C and 1400°C. The foam device was irradiated by concentrated visible light from a sun simulator at a peak flux density of 925 kW/m2 and an average flux density of 415 kW/m 2 (total power input on the surface of the foam was 0.296 kW) in a N2 gas stream
    subsequently, it was reacted with steam at 1100°C while heating by an infrared furnace. Hydrogen successfully continued to be produced in the repeated cycles. © 2009 by ASME.

    DOI: 10.1115/1.3090819

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  • Application of an internally circulating fluidized bed for windowed solar chemical reactor with direct irradiation of reacting particles 査読

    Tatsuya Kodama, Syu-Ichi Enomoto, Tsuyoshi Hatamachi, Nobuyuki Gokon

    Journal of Solar Energy Engineering, Transactions of the ASME   130 ( 1 )   0145041 - 0145044   2008年2月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)  

    Solar thermochemical processes require the development of a high-temperature solar reactor operating at 1000-1500°C, such as solar gasification of coal and the thermal reduction of metal oxides as part of a two-step water splitting cycle. Here, we propose to apply "an internally circulating fluidized bed" for a windowed solar chemical reactor in which reacting particles are directly illuminated. The prototype reactor was constructed in a laboratory scale and demonstrated on CO2 gasification of coal coke using solar-simulated, concentrated visible light from a sun simulator as the energy source. About 12% of the maximum chemical storage efficiency was obtained by the solar-simulated gasification of the coke. Copyright © 2008 by ASME.

    DOI: 10.1115/1.2807213

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  • Thermochernical cycles for high-temperature solar hydrogen production 査読

    Tatsuya Kodama, Nobuyuki Gokon

    CHEMICAL REVIEWS   107 ( 10 )   4048 - 4077   2007年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    DOI: 10.1021/cr050188a

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  • Ru/Ni-Mg-O catalyzed SiC-foam absorber for solar reforming receiver-reactor 査読

    Tatsuya Kodama, Takuya Moriyama, Takehiro Shimoyama, Nobuyuki Gokon, Hidemasa Andou, Nobuhiro Satou

    JOURNAL OF SOLAR ENERGY ENGINEERING-TRANSACTIONS OF THE ASME   128 ( 3 )   318 - 325   2006年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ASME  

    High-temperature solar reforming of methane with CO2 is investigated using a directly solar-irradiated absorber subjected to a solar mean flux level above 400 kW m(-2) (the peak flux of about 700 kW m(-2)). The new type of catalytically activated ceramic foam absorber-a Ru/Ni-Mg-O catalyzed SiC-foam absorber-was prepared, and its activity was tested in a laboratory-scale volumetric receiver-reactor with a transparent (quartz) window by using a sun-simulator Compared to conventional Rh/Al2O3 catalyzed SiC-foam absorber, this new catalytic absorber is more cost effective and is found to exhibit a superior reaction performance at the high solar flux or at high temperatures, especially above 950 degrees C. This new absorber will be applied in solar receiver-reactor systems for converting concentrated high solar fluxes to chemical fuels via endothermic natural-gas reforming at high temperatures.

    DOI: 10.1115/1.2210497

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  • Thermochemical hydrogen production by a redox system of ZrO2-supported Co(II)-ferrite 査読

    T Kodama, Y Kondoh, R Yamamoto, H Andou, N Satou

    SOLAR ENERGY   78 ( 5 )   623 - 631   2005年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    The thermochemical two-step water splitting was examined on ZrO2-supported Co(II)-ferrites below 1400 degrees C, for purpose of converting solar high-temperature heat to clean hydrogen energy as storage and transport of solar energy. The ferrite on the ZrO2-support was thermally decomposed to the reduced phase of wustite at 1400 degrees C under an inert atmosphere. The reduced phase was reoxidized with steam on the ZrO2-support to generate hydrogen below 1000 degrees C in a separate step. The ZrO2-supporting alleviated the high-temperature sintering of iron oxide. As the results, the ZrO2-supported ferrite realized a greater reactivity and a better repeatability of the cyclic water splitting than the conventional unsupported ferrites. The CoxFe3-xO4/ZrO2 with the x value of around 0.4-0.7 was found to be the promising working material for the two-step water splitting when thermally reduced at 1400 degrees C under an inert atmosphere. (c) 2004 Published by Elsevier Ltd.

    DOI: 10.1016/j.solener.2004.04.008

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  • Catalytically activated metal foam absorber for light-to-chemical energy conversion via solar reforming of methane

    T Kodama, A Kiyama, KI Shimizu

    ENERGY & FUELS   17 ( 1 )   13 - 17   2003年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    CO2 reforming of methane was examined under direct irradiation of the catalytically activated metal foam absorber by solar-simulated, concentrated visible light in the small receiver- reactor system with a transparent window. Rh, Ru, or Ni was applied as the active metal on the aluminacoated or noncoated Ni-Cr-Al metal foam disk for the preparation of the absorber. Rh showed the best activity on the noncoated metal foam while Ru was the best on the alumina-coated one. The most active and stable RU Al2O3/Ni-Cr-Al-foam absorber yielded a maximum methane conversion of 73% at a GHSV of 8500 h(-1) and at ambient pressure, in which about 50% of the incident light energy reaching the absorber was stored as chemical enthalpy at a relatively low value of the average input-power density of radiation, rho = 180 kW m(-2) (the peak flux density of 274 kW m-2 at the center of the irradiated surface of the absorber). This catalytically activate metal foam absorber will be used in the receiver-reactor system for solar methane reforming at relatively low-energy fluxes of concentrated solar radiation.

    DOI: 10.1021/ef0200525

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  • Two-step carbon dioxide thermochemical splitting using foam device of ceria and hercynite 査読

    Y. Koyama, K, Ito, S. Ohta, M. Nakakura, T. Kodama, K. J. Warren, A. W. Weimer, K. Matsubara

    Journal of Japan Solar Energy Society   49 ( 4 )   71 - 76   2023年

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.24632/jses.49.4_71

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  • A review on high‐temperature thermochemical heat storage: Particle reactors and materials based on solid–gas reactions 招待 査読

    Selvan Bellan, Tatsuya Kodama, Nobuyuki Gokon, Koji Matsubara

    WIREs Energy and Environment   11 ( 5 )   2022年5月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Wiley  

    Abstract

    In order to produce electricity beyond insolation hours and supply to the electrical grid, thermal energy storage (TES) system plays a major role in CSP (concentrated solar power) plants. Current CSP plants use molten salts as both sensible heat storage media and heat transfer fluid, to operate up to 560°C. To meet the future high operating temperature and efficiency, thermochemical storage (TCS) emerged as an attractive alternatives for next generation CSP plants. In these systems, the solar thermal energy is stored by endothermic reaction and subsequently released when the energy is needed by exothermic reversible reaction. This review compares and summarizes different thermochemical storage systems that are currently being investigated, especially TCS based on metal oxides. Various experimental, numerical, and technological studies on the development of particle reactors and materials for high‐temperature TCS applications are presented. Advantages and disadvantages of different types heat storage systems (sensible, latent, and thermochemical), and particle receivers (stacked, fluidized, and entrained), have been discussed and reported.

    This article is categorized under:Sustainable Energy &gt; Solar Energy

    Emerging Technologies &gt; Energy Storage

    Emerging Technologies &gt; Materials

    DOI: 10.1002/wene.440

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    その他リンク: https://onlinelibrary.wiley.com/doi/full-xml/10.1002/wene.440

  • Fluidization behavior of redox metal oxide and spinel particles to develop high-energy-density thermal energy storage system for concentrated solar power applications 査読

    Genta TSURUMAKI, Selvan BELLAN, Koji MATSUBARA, Tatsuya KODAMA, Mitsuho NAKAKURA, Nobuyuki GOKON, Hyun SEOK CHO, Karthik MANI, Sakthivel SHANMUGASUNDARAM

    Journal of Thermal Science and Technology   17 ( 2 )   22 - 00061   2022年

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Japan Society of Mechanical Engineers  

    DOI: 10.1299/jtst.22-00061

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  • Theoretical research aiming at high-efficiency hydrogen production using solar thermochemical energy for the goal of sustainable energy supply 査読

    Nishimura, T, Kodama, T, Sakane, G, Ishii T

    Journal of Kagawa University International Office   14   253 - 259   2022年

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  • Phase Change Material of Copper–Germanium Alloy as Solar Latent Heat Storage at High Temperatures 査読

    Nobuyuki Gokon, Chew Shun Jie, Yuya Nakano, Shogo Okazaki, Tatsuya Kodama, Tsuyoshi Hatamachi, Selvan Bellan

    Frontiers in Energy Research   9   2021年6月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Frontiers Media SA  

    A copper–germanium alloy (Cu–Ge alloy) was examined as a phase change material, at temperatures exceeding 600°C, for latent heat storage in solar thermal applications. First, the thermo-physical properties of the Cu–Ge alloy were examined using differential scanning calorimetry, thermomechanical analysis, and laser flash analysis. Second, to evaluate the thermal response and reliability of the Cu–Ge alloy, the cyclic properties of thermal charge/discharge were examined under various thermal conditions. The alloys obtained after the tests were examined for their chemical compatibility with the stainless steel container using an electron probe micro analyzer. The elemental distribution of each Cu–Ge alloy was evaluated using cyclic performance tests. Finally, the chemical compatibility of the Cu–Ge alloy was evaluated using a high-temperature test with candidate materials of a phase change material container vessel [stainless steel (SUS310S), Inconel625, silicon carbide (SiC), and alumina (Al2O3)]. The Cu–Ge alloy exhibited significant potential as a latent heat storage material in next-generation solar thermal power plants because it demonstrates various advantages, including a superior storage capacity at a temperature of 644°C, temperature coherence to the phase diagram, a quick thermal response, satisfactory cyclic behavior of charge/discharge modes, a thermodynamically stable metallographic structure, and non-reactivity with container ceramic materials (SiC and Al2O3).

    DOI: 10.3389/fenrg.2021.696213

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  • Experimental Study of Mn-CeO<inf>2</inf> Coated Ceramic Foam Device for Two-step Water Splitting Cycle Hydrogen Production with 3kW Sun-simulator 査読

    Hyun Seok Cho, Tatsuya Kodama, Nobuyuki Gokon, Selvan Bellan, Naoyoshi Nishigata

    AIP Conference Proceedings   2303   2020年12月

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    掲載種別:研究論文(国際会議プロシーディングス)  

    In this paper, the effect of doping of Manganese on to Cerium oxide for thermochemical two-step water splitting cycle for produce the hydrogen was experimentally studied. In order to compare the oxygen/hydrogen productivity, pure CeO2, coprecipitation method applied Mn-CeO2, and direct doping calcination method adopted Mn-CeO2 were used to thermo-chemical two-step water splitting cycle tests. The synthesized sample powders were coated on the reticulated porous foam device and tested in the fixed bed type reactor for the temperature of 1400 C for thermal reduction step, and 1200 C for water decomposition step through 5 cyclic tests. The redox reactive foam devices were irradiated by 3kW sun-simulator, and all samples recorded successful oxygen/hydrogen production. Among the 3 sample devices, the 15 mol% Mn-CeO2 foam device which synthesized by direct doping calcination method shows highest hydrogen production amount and H2/O2 conversion ratio. o o

    DOI: 10.1063/5.0029890

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  • Chemical compatibility of Cu-Ge alloy with container materials for latent heat storage system 査読

    Nobuyuki Gokon, Chew Shun Jie, Selvan Bellan, Tatsuya Kodama, Tsuyoshi Hatamachi, Hyunseok Cho

    AIP Conference Proceedings   2303   2020年12月

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    掲載種別:研究論文(国際会議プロシーディングス)  

    Latent heat storage technology in CSP plant has been studied to enhance the dispatchability of solar energy in order to meet fluctuating electricity needs. A novel concept using metal alloys as latent heat storage material gives way to achieve this technology. In this paper, we analyzed the structural and thermal properties of Cu-Ge alloy to evaluate the potential of metallic PCM for high temperature TES application. Containment options for metallic PCM were explored and the materials are selected for long term operation. Compatibility tests of stainless steel, alumina and SiC ceramics under inert atmosphere were performed at high temperatures (800°C) for a duration of 1 month (720 h) in order to develop a suitable container material for thermal energy storage system.

    DOI: 10.1063/5.0028722

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  • Thermochemical two-step CO<inf>2</inf> splitting using La<inf>0.7</inf>Sr<inf>0.3</inf>Mn<inf>0.9</inf>Cr<inf>0.1</inf>O<inf>3</inf> of perovskite oxide for solar fuel production 査読

    Hiroki Sawaguri, Nobuyuki Gokon, Naoki Ito, Selvan Bellan, Tatsuya Kodama, Hyun Seok Cho

    AIP Conference Proceedings   2303   2020年12月

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    掲載種別:研究論文(国際会議プロシーディングス)  

    A thermochemical two-step water-splitting cycle using perovskite oxide of La0.7Sr0.3Mn0.9Cr0.1O3 was examined for carbon monoxide production from CO2 using concentrated solar radiation. Previously, the authors proved the perovskite oxide can thermochmically split H2O via two-step process into oxygen and hydrogen in an individual step. In this study, a thermochemical two-step CO2 splitting cycle using the perovskite oxide was examined for the reactivity and repeatability of redox reaction at CO2 spitting temperatures of 1000-1200 °C. The reactivity and repeatability for two-step CO2 splitting was compared to those for H2O splitting operating at the same temperature level.

    DOI: 10.1063/5.0028681

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  • Thermochemical H<inf>2</inf>O splitting using LaSrMnCrO<inf>3</inf> of perovskite oxides for solar hydrogen production 査読

    Nobuyuki Gokon, Kazuki Hara, Naoki Ito, Hiroki Sawaguri, Selvan Bellan, Tatsuya Kodama, Hyun Seok Cho

    AIP Conference Proceedings   2303   2020年12月

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    掲載種別:研究論文(国際会議プロシーディングス)  

    A thermochemical two-step water-splitting cycle using perovskite oxide of La0.7Sr0.3Mn0.9Cr0.1O3 was examined for hydrogen production from water using concentrated solar radiation. The impact of the thermal reduction temperatures of 1000–1350 °C on oxygen/hydrogen productivity and repeatability was examined for hydrogen production at a water decomposition temperature of 1200 °C. The sample displayed relatively high evolution rates of oxygen at TR temperatures of 1350-1300°C, and showed similar rate at TR temperatures of 1000-1200 °C. After the sample was subjected to the TR step at temperatures of 1350-1300 °C, the obtained samples were superior hydrogen production rate to the others. On the other hand, the sample provided relatively good reactivities and repeatabilities for oxygen release and hydrogen production with a small production level without coagulation or sintering during the TR temperatures of 1000-1200 °C.

    DOI: 10.1063/5.0028720

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  • Numerical analysis on solidification process of PCM in triplex-tube thermal energy storage system

    Koya Hirai, Selvan Bellan, Koji Matsubara, Tatsuya Kodama, Nobuyuki Gokon, Hyun Seok Cho

    AIP Conference Proceedings   2303   2020年12月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:American Institute of Physics Inc.  

    Considerable attention is being paid in recent years to develop and improve alternative technologies to replace fossil fuels due to pollution problems and limited conventional energy sources. Solar thermal energy has been considering as one of the most attractive renewable sources to provide solution to the aforementioned problems. In recent years, latent thermal energy storage systems using phase change materials (PCMs) have been developed to aid energy supply and demand of solar thermal power plants. As one of the obstacles of these systems is the low thermal conductivity of PCMs, ceramic fin has been used in this study to enhance heat transfer rate between the PCM and heat transfer fluid. To assess the heat transfer characteristics of the triplex-tube thermal energy storage system with ceramic fin, a numerical model has been developed and the effect of fin for various Stefan numbers has been studied numerically. The heat transfer and solidification rates are significantly enhanced when connecting the fins between the inner and outer tubes.

    DOI: 10.1063/5.0028873

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  • Thermal charge/discharge performance of iron–germanium alloys as phase change materials for solar latent heat storage at high temperatures 査読

    Nobuyuki Gokon, Chew Shun Jie, Yuya Nakano, Tatsuya Kodama, Selvan Bellan, Hyunseok Cho

    Journal of Energy Storage   30   101420 - 101420   2020年8月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.est.2020.101420

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  • Direct simulation of a volumetric solar receiver with different cell sizes at high outlet temperatures (1,000–1,500 °C) 査読

    Mitsuho Nakakura, Koji Matsubara, Selvan Bellan, Tatsuya Kodama

    Renewable Energy   146   1143 - 1152   2020年2月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.renene.2019.07.039

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  • Thermochemical two-step water splitting cycle using perovskite oxides based on LaSrMnO3 redox system for solar H2 production

    Nobuyuki Gokon, Kazuki Hara, Yuta Sugiyama, Selvan Bellan, Tatsuya Kodama, Cho Hyun-seok

    Thermochimica Acta   680   2019年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier B.V.  

    A thermochemical two-step water-splitting cycle using perovskite oxides based on LaSrMnAlO3 was examined for hydrogen production from water using concentrated solar radiation. Concurrent Sr and Mn substitutions in La1-xSrxMnxAl1-xO3, Sr and Al substitutions in La1-ySryMn1-yAlyO3, and substitution of Al by Cr in La0.7Sr0.3Mn1-zCrzO3 were examined, and their kinetics, oxygen/hydrogen productivity, and repeatability were compared against LaSrMnAlO3. The impact of the chemical compositions of the perovskite oxides was systematically examined at a thermal reduction temperature of 1350 °C and water decomposition temperatures of 1000–1200 °C. From the viewpoints of average amounts of oxygen and hydrogen produced and the H2/O2 ratios, La0.7Sr0.3Mn0.9Cr0.1O3 and La0.7Sr0.3Mn0.8Cr0.2O3 provided the most reproducible productions of oxygen and hydrogen in the thermochemical two-step water-splitting cycle.

    DOI: 10.1016/j.tca.2019.178374

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  • Direct Simulation of Volumetric Solar Receiver with Highly Concentrated Radiation

    Mitsuho Nakakura, Koji Matsubara, Selvan Bellan, Tatsuya Kodama

    IOP Conference Series: Materials Science and Engineering   556 ( 1 )   2019年8月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Institute of Physics Publishing  

    The volumetric solar receiver is a promised technology for high-temperature solar absorption in the concentrated solar power, industrial solar thermal usage and solar fuel production. Existing numerical simulation separated computations of light and convective flow and two-way coupling was not perfectly integrated between radiation and convective transport. This paper describes conjugate analysis of radiation, convection and conduction heat transfer in the volumetric receiver for perfect three-way coupling between three mechanisms of heat transfer. The numerical scheme was used for the volumetric receiver with plane surface and that with cut-back inlets for optimization of the geometry. The simulation was made for single cell of honeycomb with 2.4 mm pitch and 0.5 mm wall thickness. Two cases of surface geometry was computed: plane surface
    cut-back inlet with 10 mm depth. Basic equations are momentum and energy equations with radiation transport equation. The discrete ordinates method was applied for solving the radiation intensity to consider perfect interaction between radiation, convection and conduction. The material of the receivers are assumed as stainless steel. The numerical simulation demonstrated the superiority of the cut-back receiver which increased the exit temperature by 30 K and decreased 2 Pa for the smallest beam angle of 10°. The contour plot of total heat flux on the wall revealed that the shadow effect was attenuated by the cut-back inlet leading to heat transfer enhancement. The novelties of this work are to treat perfect interaction between radiation and convection in volumetric receiver and to demonstrate the excellence of cut-back inlet receivers.

    DOI: 10.1088/1757-899X/556/1/012060

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  • Fe-doped manganese oxide redox material for thermochemical energy storage at high-temperatures 査読

    Nobuyuki Gokon, Aoi Nishizawa, Takehiro Yawata, Selvan Bellan, Tatsuya Kodama, Hyun Seok Cho

    AIP Conference Proceedings   2126   2019年7月

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AIP Publishing  

    Fe-doped manganese oxides for solar thermochemical storage are studied using thermogravimetric reactor in a laboratory scale. The operation process of Fe-doped Mn O /Mn O redox pair for two-step thermochemical cycle are optimized from the viewpoint of redox temperatures and thermochemical storage capacity, and the impact of operation temperatures on redox performances were experimentally evaluated. In addition, the thermochemical storage potentials of some Fe-X-doped manganese oxides are examined with regards to reaction rate, short-term cycling stability, storage capacity and redox temperatures. 2 3 3 4

    DOI: 10.1063/1.5117752

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  • Efficiency and heat loss analysis of honeycomb receiver varying air mass flow rate and beam width 査読

    Mitsuho Nakakura, Koji Matsubara, Selvan Bellan, Tatsuya Kodama

    International Journal of Heat and Mass Transfer   137   1027 - 1040   2019年7月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.ijheatmasstransfer.2019.03.153

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  • Thermochemical behavior of perovskite oxides based on La<inf>x</inf>Sr<inf>1-x</inf>(Mn, Fe, Co)O<inf>3-Δ</inf> and Ba<inf>y</inf>Sr<inf>1-y</inf>CoO<inf>3-Δ</inf> redox system for thermochemical energy storage at high temperatures 査読

    Nobuyuki Gokon, Takehiro Yawata, Selvan Bellan, Tatsuya Kodama, Hyun Seok Cho

    Energy   171   971 - 980   2019年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    La Sr (Mn, Fe, Co)O , and Ba Sr CoO perovskite oxide powders were investigated as potential thermochemical energy storage (TES) materials operated at high temperatures above 600 °C. The purpose of the research is to provide complete characterization of the impact of partial A- and B-site substitution on the reactivity, kinetics, redox reaction repeatability and charging/discharging storage capacity. The perovskite oxides were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) at temperatures of 500–1100 °C. Thermal energy storage was evaluated in terms of the enthalpy of the reversible reactions of oxygen release (reduction) and uptake (oxidation) upon heating the oxide materials in air stream. Among the perovskites tested, Ba Sr CoO and Ba Sr CoO powders were suitable thermochemical storage materials operating at above 600 °C in terms of chemical reactivity, charging/discharging temperatures and storage capacities, kinetics of oxygen uptake/release, and repeatability of thermochemical cycling. Further, charging/discharging capacity for both perovskites was comparable to that for Fe-doped manganese oxide. x 1-x 3-δ y 1-y 3-δ 0.3 0.7 3-δ 0.7 0.3 3-δ

    DOI: 10.1016/j.energy.2019.01.081

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  • Thermal performance of a 30 kW fluidized bed reactor for solar gasification: A CFD-DEM study 査読

    Selvan Bellan, Tatsuya Kodama, Koji Matsubara, Nobuyuki Gokon, Hyun Seok Cho, Kousuke Inoue

    Chemical Engineering Journal   360   1287 - 1300   2019年3月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.cej.2018.10.111

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  • Development of a 5kW<inf>th</inf> internally circulating fluidized bed reactor containing quartz sand for continuously-fed coal-coke gasification and a beam-down solar concentrating system 査読

    Nobuyuki Gokon, Satoshi Kumaki, Yosuke Miyaguchi, Selvan Bellan, Tatsuya Kodama, Hyunseok Cho

    Energy   166   1 - 16   2019年1月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    The operational mode of a batch-type fluidized bed reactor containing quartz sand and coal-coke particles was tested under xenon arc lamp (Xe-light) illumination to develop processes for the continuous feeding and gasification of coke particles in the quartz sand fluidized bed. This paper focuses on the fluidizing, heating, and steam gasification performances of a windowed internally circulating fluidized bed reactor. The operational modes explored in this study were: (1) elevated temperature processes associated with the use of Xe-light radiation to reach gasification temperatures, and, (2) the gasification process driving steam gasification at high-temperatures, working with stream gasification of continuously-fed coal-coke. The gasification performances were used to evaluate the performance of quartz sand as a thermal-transfer/sensible heat-storage medium. The peak rate of gas production was greatly enhanced for the high volume fraction of coal-coke. In addition, the light-to-energy conversion rate of 11.0–13.2% and carbon conversion rate up to 80% were reached in the simplified distributor structure of gasification reactor.

    DOI: 10.1016/j.energy.2018.10.036

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  • Heat transfer and fluid flow analysis of a fluidized bed reactor for beam-down optics 査読

    Selvan Bellan, Tatsuya Kodama, Koji Matsubara, Nobuyuki Gokon, Hyun Seok Cho

    AIP Conference Proceedings   2126   180004   2019年

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    掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AIP Publishing  

    DOI: 10.1063/1.5117684

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  • Preliminary tests of batch type fluidized bed reactor for development of continuously-feeding fluidized bed reactor - An elevated temperature and gasification processes 査読

    Nobuyuki Gokon, Shinpei Takagi, Selvan Bellan, Hyun Seok Cho, Tatsuya Kodama

    AIP Conference Proceedings   2033   2018年11月

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    掲載種別:研究論文(国際会議プロシーディングス)  

    A laboratory-scale prototype windowed internally circulating fluidized-bed reactor made of quartz sand and coal coke particles was investigated for steam gasification using concentrated Xe-light radiation as the energy source. The quartz sand was used as a chemically inert bed material for the fluidized bed, while the coal coke particles functioned as the reacting particles for the endothermic gasification reaction. The purpose of this study is a preliminary tests of batch type fluidized bed reactor that assuming a continuous feeding process of carbonous materials (cokes, coal, and biomass et al.) into the fluidized bed reactor with a thermal transfer/storage medium (quartz sand). The gasification performances such as the production rates of CO, H , and CO were evaluated for the fluidized bed reactor. 2 2

    DOI: 10.1063/1.5067140

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  • Particle fluidized bed receiver/reactor with a beam-down solar concentrating optics: Performance test of two-step water splitting with ceria particles using 30-kWth sun-simulator

    Tatsuya Kodama, Nobuyuki Gokon, Hyun Seok Cho, Selvan Bellan, Koji Matsubara, Kousuke Inoue

    AIP Conference Proceedings   2033   2018年11月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:American Institute of Physics Inc.  

    The first performance test of a novel windowed solar fluidized bed reactor was carried out for a two-step water splitting cycle with ceria particles by using a 30-kWth sun-simulator. O2 and H2 were successfully produced by the reactor system. During the thermal reduction step of the two-step water splitting, a fluidized bed of ceria particles was created by passing N2 gas through the perforated bottom plate of the reactor, and about 30 kWth of high flux visible light from 19 xenon-arc lamps of the sun-simulator was directed inside the reactor through a quartz window to directly irradiate the top of the fluidized bed. The central bed temperature reached the temperature of 1400 to 1500°C in the thermal reduction step. The subsequent water decomposition or hydrolysis step was performed at the central bed temperature of 800 - 900°C. About 6 - 12 Ndm3 of hydrogen was produced by one cycle.

    DOI: 10.1063/1.5067143

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  • CFD-DEM investigation on flow and temperature distribution of ceria particles in a beam-down fluidized bed reactor

    Selvan Bellan, Koji Matsubara, Hyun Seok Cho, Nobuyuki Gokon, Tatsuya Kodama

    AIP Conference Proceedings   2033   2018年11月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:American Institute of Physics Inc.  

    In this research, heat transfer and hydrodynamics of a solar thermochemical fluidized bed reactor filled with ceria particles have been studied numerically and experimentally for beam-down solar concentrating system. A CFD-DEM model has been developed, in which the contact forces between the particles have been calculated by the spring-dashpot model, based on the soft-sphere method. An experimental visualization of particles circulation pattern and mixing of two-tower fluidized bed system has been presented. Simulation results have been compared with experimental data to validate the CFD-DEM model. Results indicate that the model can predict the particle-fluid flow of the two-tower fluidized bed reactor. Using this model, the key operating parameters can be optimized.

    DOI: 10.1063/1.5067137

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  • Numerical and experimental study on granular flow and heat transfer characteristics of directly-irradiated fluidized bed reactor for solar gasification 査読

    Selvan Bellan, Nobuyuki Gokon, Koji Matsubara, Hyun Seok Cho, Tatsuya Kodama

    International journal of hydrogen energy   43 ( 34 )   1 - 15   2018年8月

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    掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.ijhydene.2018.06.033

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  • Conjugate radiation-convection-conduction simulation of volumetric solar receivers with cut-back inlets 査読

    Mitsuho Nakakura, Selvan Bellan, Koji Matsubara, Tatsuya Kodama

    Solar Energy   170   606 - 617   2018年8月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.solener.2018.06.006

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  • A CFD-DEM study of hydrodynamics with heat transfer in a gas-solid fluidized bed reactor for solar thermal applications 査読

    Selvan Bellan, Koji Matsubara, Hyun Seok Cho, Nobuyuki Gokon, Tatsuya Kodama

    International Journal of Heat and Mass Transfer   116   377 - 392   2018年1月

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    掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/j.ijheatmasstransfer.2017.09.015

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  • Gas-solid flow and heat transfer characteristics of a fluidized bed reactor for solar thermal applications

    Selvan Bellan, Koji Matsubara, Nobuyuki Gokon, Tatsuya Kodama, Hyun Seok Cho, Issei Tsuchida

    International Heat Transfer Conference   2018-   6519 - 6527   2018年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Begell House Inc.  

    In concentrated solar thermal industry, fluidized-bed technology has been used to produce hydrogen and synthetic gas by two-step water splitting cycles and gasification of coal cokes respectively. A two tower fluidized bed reactor has been developed in this study for solar thermochemical conversions. To study the granular flow and heat transfer characteristics of the two tower fluidized bed reactor, a numerical model has been developed by combined approach of discrete element method and computational fluid dynamics. Particle collision dynamics has been solved by the spring-dashpot model based on the soft-sphere method. Discrete ordinate radiation model has been used to solve the radiative transfer equation. To validate the model, the predicted heat transfer characteristics of the bed have been compared with the reported experimental data. A reasonable agreement has been found between the predicted and experimental results. Particulate flow dynamics of the bed filled with ceria powder is presented with temperature distributions. Using this model, the key operating parameters can be optimized.

    DOI: 10.1615/ihtc16.mpf.023665

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  • Conjugated radiation-convection-conduction heat transfer analysis of volumetric receiver with highly concentrated radiation

    Mitsuho Nakakura, Selvan Bellan, Hyun-Seok Cho, Koji Matsubara, Nobuyuki Gokon, Tatsuya Kodama

    International Heat Transfer Conference   2018-   7866 - 7873   2018年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:Begell House Inc.  

    This study focuses on the conjugate radiation-convection-conduction heat-transfer problem for a square channel of volumetric solar receiver with concentrated irradiation for Concentrated Solar Power (CSP). A single channel of a honeycomb receiver is directly irradiated from the outside, via a transparent wall. Atmospheric air flows through the channel and absorbs the sensible heat. Governing equations are continuity, Navier-Stokes and energy equations for solid/fluid region, and radiative transfer equation. Radiation was solved by the Discrete Ordinates (DO) model. The effects of the number of mesh grids and direction vectors on the DO model were confirmed to be negligible. This study analyzed the heat-transfer performance of stainless-steel receivers with different channel geometry. Three different types and sizes of channels were treated
    L-shaped cuts were made at the channel top. The heat transfer performance of these channels, i.e. bulk air temperature and pressure drop at the outlet were improved by the L-shape cutting. The wall heat flux difference between simple and cut channel was clarified by the contour plots of inner walls. Across the entire inner wall, the conduction heat flux contributed to the heating of the flowing air, while the radiation heat-flux dominated near the inlet due to high incident radiation. As a result, the wall heat-flux had characteristic profile along the channel depth (-z) direction. This study elucidates conjugate heat transfer mechanism in the honeycomb-like channel receivers with highly concentrated radiation.

    DOI: 10.1615/ihtc16.nee.023436

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  • Buoyancy-opposed volumetric solar receiver with beam-down optics irradiation 査読

    Mitsuho Nakakura, Koji Matsubara, Hyun-Seok Cho, Tatsuya Kodama, Nobuyuki Gokon, Selvan Bellan, Kazuo Yoshida

    Energy   141   2337 - 2350   2017年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier Ltd  

    This paper describes a volumetric solar receiver that is vertically integrated with beam-down optics for condensed light irradiation. The heat-transfer performance of a silicon carbide honeycomb receiver was investigated using a 30-kWth solar simulator and numerical simulation. The experiments achieved an air temperature of 840 K at the receiver outlet by varying the operational parameters. Numerical simulations were performed for a vertical honeycomb block with beam-down irradiation and a horizontal honeycomb block with tower-type irradiation to elucidate the effects of buoyancy. Three blocks with different sizes were simulated for a variety of operational parameters. When the block was oriented vertically, the flow and temperature fields remained nearly symmetric in and near the receiver. In contrast, when it was oriented horizontally, the flow and temperature became asymmetric, with the hot spot moving toward the receiver's side wall and the stream in the receiver being reversed. The vertical orientation's robustness to buoyancy effects prevented any reduction in the receiver efficiency or outlet temperature and suppressed the thermal leakage.

    DOI: 10.1016/j.energy.2017.11.147

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  • CFD-DEM investigation of particles circulation pattern of two-tower fluidized bed reactor for beam-down solar concentrating system 査読

    Selvan Bellan, Koji Matsubara, Cho Hyun Cheok, Nobuyuki Gokon, Tatsuya Kodama

    POWDER TECHNOLOGY   319   228 - 237   2017年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    In this study, a numerical model has been developed by the combined approach of computational fluid dynamics (CFD) and discrete element method (DEM) collisional model to study the particle-fluid flow of the fluidized bed reactor for solar beam-down concentrating system. The contact forces between the particles have been calculated by the spring-dashpot model, based on the soft-sphere method. An experimental visualization of particles circulation pattern and mixing of two-tower fluidized bed system has been presented. A good agreement has been found between the experimental measurements and numerical predictions. To investigate the influence of fluid flow rate and particle size on the flow pattern of the reactor, simulations have been performed for various conditions. The results indicate that the large size particles induce three-dimensional effects as they are accumulated at the central axis region. The average bed height of the left tower increased by 23.4% when increasing the flow rate about 70%. (C) 2017 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.powtec.2017.06.060

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  • Development and Experimental Study for Hydrogen Production from the Thermochemical Two-step Water Splitting Cycles with a CeO2 Coated New Foam Device Design Using Solar Furnace System 査読

    Hyun Seok Cho, Tatsuya Kodama, Nobuyuki Gokon, Jong Kyu Kim, Sang Nam Lee, Yong Heack Kang

    AIP Conf. Proc.   1850   100003   2017年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER INST PHYSICS  

    A solar reactor containing a CeO2-coated reactive foam device for producing hydrogen via a thermochemical two-step water splitting cycle was proposed and experimentally tested. Modeling of the optical properties of the 40 kW(th) KIER (Korea Institute of Energy Research) solar furnace was performed to design and prepare the optimized foam matrix shape and the new solar reactor. Solar demonstration of the solar reactor was accomplished in the KIER 40 kW(th) solar furnace and hydrogen was produced successfully during the water decomposition step. The conical shape foam device was suggested and tested the temperature gradients and hydrogen productivity. Finally, five cyclic test was conducted with the conical shape CeO2-coated foam device, the total hydrogen production was 1394.32 Ncm(3) during the five cycles and the average hydrogen production per cycle was 278.86 Ncm(3).

    DOI: 10.1063/1.4984460

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  • Thermal Storage/Discharge Performances of Cu-Si Alloy for Solar Thermochemical Process 査読

    Nobuyuki Gokon, Tomoya Yamaguchi, Hyun-seok Cho, Selvan Bellan, Tsuyoshi Hatamachi, Tatsuya Kodama

    INTERNATIONAL CONFERENCE ON CONCENTRATING SOLAR POWER AND CHEMICAL ENERGY SYSTEMS (SOLARPACES 2016)   1850   2017年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER INST PHYSICS  

    The present authors (Niigata University, Japan) have developed a tubular reactor system using novel "double-walled" reactor/receiver tubes with carbonate molten-salt thermal storage as a phase change material (PCM) for solar reforming of natural gas and with Al-Si alloy thermal storage as a PCM for solar air receiver to produce high-temperature air. For both of the cases, the high heat capacity and large latent heat (heat of solidification) of the PCM phase circumvents the rapid temperature change of the reactor/receiver tubes at high temperatures under variable and uncontinuous characteristics of solar radiation. In this study, we examined cyclic properties of thermal storage/discharge for Cu-Si alloy in air stream in order to evaluate a potentiality of Cu-Si alloy as a PCM thermal storage material. Temperature-increasing performances of Cu-Si alloy are measured during thermal storage (or heat-charge) mode and during cooling (or heat-discharge) mode. A oxidation state of the Cu-Si alloy after the cyclic reaction was evaluated by using electron probe micro analyzer (EPMA).

    DOI: 10.1063/1.4984465

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  • Particles Fluidized Bed Receiver/Reactor Tests with Quartz Sand Particles Using a 100-kW(th) Beam-Down Solar Concentrating System at Miyazaki 査読

    Tatsuya Kodama, Nobuyuki Gokon, Hyun Seok Cho, Koji Matsubara, Hiroshi Kaneko, Kazuya Senuma, Sumie Itoh, Shin-nosuke Yokota

    INTERNATIONAL CONFERENCE ON CONCENTRATING SOLAR POWER AND CHEMICAL ENERGY SYSTEMS (SOLARPACES 2016)   1850   2017年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER INST PHYSICS  

    A window-type, solar fluidized bed receiver with quartz sand particles was tested by a 100-kWth novel beam-down solar concentrating system at Miyazaki, Japan. A compound parabolic concentrator (CPC) was placed above the quartz window of the receiver to increase the concentration of the solar fluxes from the beam-down solar concentrating system. The solar tests were performed in the middle of December, 2015. The central bed temperature of the receiver was reached around 960-1100 degrees C. It was found that only 20 Ndm(3)/min of air flow rate was enough to create the uniform fluidization of the particles at the given temperature range. It was predicted that if the central bed temperature could have been higher than 1100 degrees C if solar receiver test had conducted in other seasons than winter. The next solar campaign of the receiver test will be carried out in October, 2016.

    DOI: 10.1063/1.4984469

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  • Numerical Analysis of Fluid Flow and Heat Transfer During Melting Inside a Cylindrical Container for Thermal Energy Storage System 査読

    Selvan Bellan, Cho Hyun Cheok, Nobuyuki Gokon, Koji Matsubara, Tatsuya Kodama

    INTERNATIONAL CONFERENCE ON CONCENTRATING SOLAR POWER AND CHEMICAL ENERGY SYSTEMS (SOLARPACES 2016)   1850   2017年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER INST PHYSICS  

    This paper presents a numerical analysis of unconstrained melting of high temperature(&gt;1000K) phase change material (PCM) inside a cylindrical container. Sodium chloride and Silicon carbide have been used as phase change material and shell of the capsule respectively. The control volume discretization approach has been used to solve the conservation equations of mass, momentum and energy. The enthalpy-porosity method has been used to track the solidliquid interface of the PCM during melting process. Transient numerical simulations have been performed in order to study the influence of radius of the capsule and the Stefan number on the heat transfer rate. The simulation results show that the counter-clockwise Buoyancy driven convection over the top part of the solid PCM enhances the melting rate quite faster than the bottom part.

    DOI: 10.1063/1.4984427

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  • Cyclic thermal storage/discharge performances of a hypereutectic Cu-Si alloy under vacuum for solar thermochemical process 査読

    Nobuyuki Gokon, Tomoya Yamaguchi, Tatsuya Kodama

    ENERGY   113   1099 - 1108   2016年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    A copper-silicon alloy (Cu-Si alloy) was examined and evaluated as a phase-change material (PCM) for thermal energy storage applications such as load shaving and peak load shifting when coupled to a solar thermochemical reactor, reformer, or gasifier for the production of solar fuel. The Cu-Si alloy was selected as a high-temperature PCM thermal storage medium alternative to molten carbonate salts, and the compatibility of this alloy with a graphite-carbon encapsulation material was experimentally examined. The cyclic thermal storage/discharge properties of the Cu-Si alloy as a latent-heat energy storage material were studied with respect to thermal cycles. A thermal stability test was performed on Cu-20 wt% Si, Cu-25 wt% Si, and Cu-30 wt% Si alloys placed in a graphite container under vacuum. The performances of the Cu-Si alloys with increasing and decreasing temperature were measured during the thermal storage (heat-charge) and cooling (heat-discharge) modes, respectively. The elemental distribution of each Cu-Si alloy after the cyclic reaction was evaluated using an electron probe microanalyzer (EPMA). The heat storage capacities before and after the cyclic reaction were evaluated using differential scanning calorimetry (DSC) and were compared to the thermal storage properties of the molten carbonate salt. (C) 2016 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.energy.2016.07.005

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  • Cold Test with a Benchtop Set-up for Fluidized Bed Reactor Using Quartz Sand to Simulate Gasification of Coal Cokes by Concentrated Solar Radiation 査読

    Nobuyuki Gokon, Tomoaki Tanabe, Tadaaki Shimizu, Tatsuya Kodama

    SOLARPACES 2015: INTERNATIONAL CONFERENCE ON CONCENTRATING SOLAR POWER AND CHEMICAL ENERGY SYSTEMS   1734   2016年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER INST PHYSICS  

    The impacts of internal circulation of a mixture of coal-coke particles and quartz sand on the fluidization state in a fluidized bed reactor are investigated by a cold test with a benchtop set-up in order to design 10-30 kWth scale prototype windowed fluidized-bed reactor. Firstly, a basic relationship between pressure loss of inlet gas and gas velocity was experimentally examined using quartz sand with different particle sizes by a small-scale quartz tube with a distributor at ambient pressure and temperature. Based on the results, an appropriate particle range of quartz sand and layer height/layer diameter ratio (L/D ratio) was determined for a design of the fluidized bed reactor. Secondly, a windowed reactor mock-up was designed and fabricated for solar coke gasification using quartz sand as a bed material. The pressure loss between the inlet and outlet gases was examined, and descending cokes and sand particles on the sidewall of the reactor was observed in the reactor mock-up. The moving velocity and distance of descending particles/sands from the top to bottom of fluidized bed were measured by the visual observation of the colored tracer particles on outside wall of the reactor.

    DOI: 10.1063/1.4949204

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  • Particles Fluidized Bed Receiver/Reactor with a Beam-Down Solar Concentrating Optics: 30-kW(th) Performance Test Using a Big Sun-Simulator 査読

    Tatsuya Kodama, Nobuyuki Gokon, Hyun Seok Cho, Koji Matsubara, Tetsuro Etori, Akane Takeuchi, Shin-nosuke Yokota, Sumie Ito

    SOLARPACES 2015: INTERNATIONAL CONFERENCE ON CONCENTRATING SOLAR POWER AND CHEMICAL ENERGY SYSTEMS   1734   2016年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER INST PHYSICS  

    A novel concept of particles fluidized bed receiver/reactor with a beam-down solar concentrating optics was performed using a 30-kW(th) window type receiver by a big sun-simulator. A fluidized bed of quartz sand particles was created by passing air from the bottom distributor of the receiver, and about 30 kW(th) of high flux visible light from 19 xenon-arc lamps of the sun-simulator was directly irradiated on the top of the fluidized bed in the receiver through a quartz window. The particle bed temperature at the center position of the fluidized bed went up to a temperature range from 1050 to 1200 degrees C by the visible light irradiation with the average heat flux of about 950 kW/m(2), depending on the air flow rate. The output air temperature from the receiver reached 1000 - 1060 degrees C.

    DOI: 10.1063/1.4949206

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  • Oxygen and hydrogen productivities and repeatable reactivity of 30-mol%-Fe-, Co-, Ni-, Mn-doped CeO2?δ for thermochemical two-step water-splitting cycle 査読

    Nobuyuki Gokon, Toshinori Suda, Tatsuya Kodama

    Energy   90   1280 - 1289   2015年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    DOI: 10.1016/j.energy.2015.06.085

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  • Steam gasification of coal cokes by internally circulating fluidized-bed reactor by concentrated Xe-light radiation for solar syngas production 査読

    Nobuyuki Gokon, Takuya Izawa, Tatsuya Kodama

    ENERGY   79   264 - 272   2015年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    A laboratory-scale prototype windowed reactor using a fluidized bed of coal coke particles was tested for thermochemical gasification using concentrated Xe light radiation as an energy source. The fluidized-bed reactor, designed to be combined with a solar reflective tower or beam-down optics, is evaluated for steam gasification of coal coke according to gasification performance: CO, H-2, and CO2 production rates; carbon conversion; light-to-chemical efficiency. Internal circulation of coal coke particles inside the reactor increases gasification performance, which is further enhanced by higher steam partial pressure of the inlet gas. (C) 2014 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.energy.2014.11.012

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  • Redox and fluidization performances of Co3O4/CoO for solar Thermochemical energy storage 査読

    N. Gokon, S. Yokota, H. S. Cho, T. Hatamachi, T. Kodama

    ISES Solar World Congress 2015, Conference Proceedings   806 - 815   2015年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:International Solar Energy Society  

    Thermochemical energy storage using redox pair of Co3O4/CoO powders was studied for thermal energy storage (TES) using concentrated solar radiation as the energy source. Reversible chemical reactions (reduction - oxidation redox cycles) of oxides under air atmosphere are used to storage significant thermal energy via the enthalpies of the chemical reactions at high-temperature. A promising concept for solar TES is proposed using fluidized bed with Co3O4/CoO redox pair. In the present study, the effects of particles size of Co3O4/CoO powders on thermochemical storage performances are investigated in order to explore the potential of the material for fluidized-particle bed reactor. The Co3O4 powders with particle sizes of 100-200, 200-300, 300-500 and 500-700 μm were used to test redox performances by thermo-gravimetric analysis. A flowability (fluidization state) of Co3O4 powders in a fluidized bed reactor for thermochemical energy storage is also examined in this study. A basic relationship between pressure drop of inlet gas and gas flow rate was experimentally examined using bed materials with different particle sizes by a small-scale quartz reactor at ambient pressure and temperature.

    DOI: 10.18086/swc.2015.04.25

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  • Laboratory experiment and simulation of higherature fluidized bed air receiver for concentrated solar power generation 査読

    Koji Matsubara, Yuki Kazuma, Atsushi Sakurai, Tatsuya Kodama, Nobuyuki Gokon, Hyun-Seok Cho, Kazuo Yoshida, Yoshinori Nagase

    Nihon Enerugi Gakkaishi/Journal of the Japan Institute of Energy   94 ( 11 )   1323 - 1329   2015年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Japan Institute of Energy  

    This study proposes a t wo-tower t ype fluidized receiver for receiving concentrated s olar light at high temperatures is proposed. This fluidized receiver is coupled with the Miyazaki beam-down reflector system. The visualization and the numerical simulation was made for the laboratory model to show the fluid-dynamics and the heat transport as well as to elaborate the existing demonstration model. The experimental visualization of the cold model demonstrated that in each tower, the particles are moved by the aerated organized flow. The numerical simulation was made using the thermal input cited from the 5.0kWth sun simulator. The numerical simulation demonstrated that the inner particles are heated above 950 °C after 3.0 minutes of the aeration start time. The increase in temperature is caused by the intrusion of the heated particles from the high-pressure side tower to the low-pressure side tower. It is thus suggested that collective circulation occurs between high- and low-pressure side towers and this can be utilized for a direct thermal storage system.

    DOI: 10.3775/jie.94.1323

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  • Cold testings of a windowed fluidized bed reactor using quartz sand for solar gasification of coke 査読

    N. Gokon, T. Tanabe, H. S. Cho, T. Hatamachi, T. Kodama

    ISES Solar World Congress 2015, Conference Proceedings   799 - 805   2015年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:International Solar Energy Society  

    A windowed fluidized bed reactor prototype was studied and developed for solar thermochemical gasification of coal cokes with steam and CO2. The windowed fluidized bed reactor is assumed to be combined with a newly developed beam-down optics. Recently, quartz sand was employed as a chemically-inert bed material for the fluidized bed and worked as a thermal transfer/storage medium inside the reactor for coke gasification under direct light irradiation. In order to design a laboratory-scale prototype windowed fluidized-bed containing of quartz sand and coke particles, the reactor model of fluidized bed was made from a transparent acrylic resin to allow us to observe a fluidizing particle through the sidewall of the reactor body
    a branching tube is equipped with the sidewall of the reactor to continuously supply coal-coke particles from a screw feeder. In the present study, in order to evaluate fluidization performance of coal-cokes, the pressure loss between the inlet and outlet gases was examined, and descending coal-coke particles on the sidewall of the reactor was observed in the reactor model. The moving velocity and distance of descending particles from the top to bottom of fluidized bed were measured by the visual observation of the tracer particles on outside wall of reactor model.

    DOI: 10.18086/swc.2015.04.24

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  • Steam gasification of coal cokes in an internally circulating fluidized bed of thermal storage material for solar thermochemical processes 査読

    Nobuyuki Gokon, Takuya Izawa, Takehiko Abe, Tatsuya Kodama

    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY   39 ( 21 )   11082 - 11093   2014年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    A laboratory-scale prototype windowed internally circulating fluidized-bed reactor made of quartz sand and coal coke particles was investigated for steam gasification using concentrated Xe-light radiation as the energy source. The quartz sand was used as a chemically inert bed material for the fluidized bed, while the coal coke particles functioned as the reacting particles for the endothermic gasification reaction. The advantages of using quartz sand as the bed material for the directly irradiated gasification reactor are as follows: (1) The bed height is maintained at a constant level during the gasification. (2) The quartz sand functions as a thermal transfer/storage medium inside the reactor. The gasification performances such as the production rates of CO, H-2, and CO2; carbon conversion; and light-to-chemical energy conversion were evaluated for the fluidized-bed reactor with a thermal transfer/storage medium (quartz sand). The effects of using the bed material (quartz sand) on the gasification performance are described in this paper. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2014.05.124

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  • Steam reforming of methane using double-walled reformer tubes containing high-temperature thermal storage Na2CO3/MgO composites for solar fuel production 査読

    Nobuyuki Gokon, Shohei Nakamura, Tsuyoshi Hatamachi, Tatsuya Kodama

    ENERGY   68   773 - 782   2014年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Double-walled reactor tubes containing thermal storage materials based on the molten carbonate salts-100 wt% Na2CO3 molten salt, 90 wt% Na2CO3/10 wt% MgO and 80 wt% Na2CO3/20 wt% MgO composite materials were studied for the performances of the reactor during the heat charging mode, while those of methane reforming with steam during heat discharging mode for solar steam reforming. The variations in the temperatures of the catalyst and storage material, methane conversion, duration of reforming for obtaining high levels of methane conversion (&gt; 90%), higher heating value (HHV) power of reformed gas and efficiency of the reactor tubes were evaluated for the double-walled reactor tubes and a single-wall reactor tube without the thermal storage. The results for the heat charging mode indicated that the composite thermal storage could successfully store the heat transferred from the exterior wall of the reactor in comparison to the pure molten-salt. The double-walled reactor tubes with the 90 wt% Na2CO3/10 wt% MgO composite material was the most desirable for steam reforming of methane to realize large HHV amounts of reformed gas and higher efficiencies during heat-discharging mode. (C) 2014 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.energy.2014.01.107

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  • Carbonate molten-salt absorber/reformer: heating and steam reforming performance of reactor tubes 査読

    N. Gokon, S. Nakamura, K. Matsubara, T. Kodama

    PROCEEDINGS OF THE SOLARPACES 2013 INTERNATIONAL CONFERENCE   49   1940 - 1949   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELSEVIER SCIENCE BV  

    Steam reforming of methane is a candidate process for converting concentrated high-temperature solar heat to chemical fuels because it is a high-temperature, highly endothermic process. We developed a tubular reformer system using novel double-walled reactor tubes with molten-salt thermal storage for solar reforming to produce hydrogen or synthetic gas (CO + H-2) from a gas mixture of methane and steam using concentrated solar radiation as an energy source. The high heat capacity and large latent heat (heat of solidification) of the molten salt circumvents rapid temperature changes in the reactor tubes at high temperatures under fluctuating insolation. In this paper, we focused on under intermittent heating-cooling mode, the steam reforming performance of double-walled reactor tubes with Na2CO3/MgO composite thermal storage in comparison to pure Na2CO3 thermal storage. A heating mode using an electric furnace simulates reactor startup in the morning and reheating of the reactor by concentrated solar radiation after brief periods of cloud passage. The intermittent heating-cooling mode simulates fluctuating incident solar radiation during cyclic short-term cloud passage. The temperature variations of the catalyst and storage material, methane conversion, and higher heating value power of the reformed gas were examined for the double-walled reactor tubes and a single-wall (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

    DOI: 10.1016/j.egypro.2014.03.206

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  • Kinetics of thermal reduction step of thermochemical two-step water splitting using CeO2 particles: Master-plot method for analyzing non-isothermal experiments 査読

    T. Ishida, N. Gokon, T. Hatamachi, T. Kodama

    PROCEEDINGS OF THE SOLARPACES 2013 INTERNATIONAL CONFERENCE   49   1970 - 1979   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELSEVIER SCIENCE BV  

    Thermochemical two-step water splitting cycle by concentrated solar heat has been studied as an energy conversion of solar energy into hydrogen energy. The thermochemical two-step water splitting cycle using metal oxide redox pair was composed of thermal reduction (T-R) step of metal oxide at higher temperature to release oxygen and, subsequent water decomposition (W-D) step of the reduced metal oxide with steam at lower temperature to produce hydrogen. Recently, cerium oxide (CeO2) is concerned as a redox pair of the thermochemical cycle for highly reactivity and cyclicity at high temperature. In this study, we focused a kinetic analysis of thermochemical two-step water splitting using cerium oxide. Various theoretical reaction models for thermal reduction (T-R) step of CeO2 particles are examined, and the appropriate reaction model for experimental results of thermogravimetric analysis was found by Master plot method. Finally, the reaction rate equation of thermal reduction is estimated. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

    DOI: 10.1016/j.egypro.2014.03.209

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  • Solar demonstration of thermochemical two-step water splitting cycle using CeO2/MPSZ ceramic foam device by 45kW(th) KIER solar furnace 査読

    H. S. Cho, T. Myojin, S. Kawakami, N. Gokon, T. Kodama, Y. H. Kang, S. N. Lee, K. K. Chai, H. K. Yoon, H. J. Lee

    PROCEEDINGS OF THE SOLARPACES 2013 INTERNATIONAL CONFERENCE   49   1922 - 1931   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELSEVIER SCIENCE BV  

    The joint international project of Niigata University (Japan) - Korea Institute of Energy Research, KIER (Korea) on the "Solar demonstration of Water-Splitting Reactor using Ceramic Foam Device" aims to develop a novel-type of solar reactor with reactive cerium oxide foam devices for high-temperature two-step thermochemical water splitting cycle, and to demonstrate its performances on sun with a 45-kW(th) solar furnace. The reactive CeO2 foam device for the two-step water splitting is proposed and prepared by Niigata University, Japan, and involves coating inert zirconia foam with reactive CeO2. The project includes the development of reactive foam devices, the new design and the fabrication of solar reactor with the reactive foam devices, and finally the solar demonstration on the KIER's 45-kW(th) solar furnace in Korea. In this paper, highly-active CeO2 particles were used as a redox material for preparing CeO2 foam devices. A ceramic foam disk made of MgO partially-stabilized Zirconia (MPSZ) was used as a ceramic matrix that was coated with the CeO2 particles. Solar thermochemical two-step water splitting was demonstrated with solar furnace in Korea system using the prepared CeO2-coated MPSZ (CeO2/MPSZ) foam devices. The prepared CeO2/MPSZ foam device has a diameter of 15 and 20cm and thickness of 2.5 cm, the loading of CeO2 was set to approximately 20 wt%.
    Then, the temperatures of the foam device at a center position were 1400-1600 degrees C for the T-R step, and 900-1100 degrees C for the subsequent W-D step. Hydrogen was successfully produced from the CeO2-MPSZ foam by a solar thermochemical two-step water-splitting, and the rate of hydrogen production and CeO2 conversion using 15 cm CeO2/MPSZ foam device were 215.6 mL/min and 3.67%, at 1st cycle. We also performed continuous testing for 20 cm diameter of the CeO2-MPSZ device, the rate of hydrogen production and CeO2 conversion were 443 ml/min and 3.27%, 1st cycle. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

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  • Thermochemical two-step water splitting cycle using Ni-ferrite and CeO2 coated ceramic foam devices by concentrated Xe-light radiation 査読

    S. Kawakami, T. Myojin, H. -S. Cho, T. Hatamachi, N. Gokon, T. Kodama

    PROCEEDINGS OF THE SOLARPACES 2013 INTERNATIONAL CONFERENCE   49   1980 - 1989   2014年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:ELSEVIER SCIENCE BV  

    Nickel ferrite (NiFe2O4) and pure cerium oxide (CeO2) supported on monoclinic zirconia (NiFe2O4/m-ZrO2) are proposed as promising redox materials for the production of hydrogen from water via a thermochemical two-step water splitting cycle. Ceramic foam devices coated with NiFe2O4/m-ZrO2 or pure CeO2 particles are prepared as a receiver/reactor operating a thermochemical water splitting cycle to produce hydrogen. The foam devices are examined in a directly irradiated receiver/reactor by a sun simulator on a laboratory scale. The purpose of this study is to examine the evolution of oxygen and hydrogen during the cyclization reaction different thermal-reduction (T-R) temperatures of 1450 and 1550 degrees C, and to compare the reproducible and stoichiometric oxygen/hydrogen production for both foam devices through a repeatable two-step reaction. In this study, a zirconia ceramic foam was used as a matrix for the reacting materials of NiFe2O4/m-ZrO2 or CeO2 particles. The zirconia ceramic foam has a diameter of 60 mm, a thickness of 15 mm, and a porosity of 10 cpi (cell number per linear inch). The loading amounts of reacting materials are 5 wt% for NiFe2O4/m-ZrO2 and 40 wt% for CeO2 particles. A concentrated Xe-beam is radiated to the foam device in a N-2 stream for the T-R step and in a N-2/steam gas mixture for the subsequent water-decomposition (W-D) step. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/3.0/).

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  • Comparative study of activity of cerium oxide at thermal reduction temperatures of 1300-1550 degrees C for solar thermochemical two-step water-splitting cycle 査読

    Nobuyuki Gokon, Sachi Sagawa, Tatsuya Kodama

    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY   38 ( 34 )   14402 - 14414   2013年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Thermochemical two-step water-splitting using CeO2 (cerium oxide) particles was studied to examine oxygen and hydrogen productivity and repeatability at thermal reduction (T-R) temperatures of 1300-1550 degrees C and water decomposition (W-D) temperatures of 400-1000 degrees C for the production of hydrogen from water using concentrated solar radiation as the energy source. The temperature dependency of oxygen and hydrogen productivity and the cyclic repeatability of CeO2 are reported in this paper. The characteristic features of CeO2 particles in the thermochemical two-step water-splitting cycle are compared with the well-known highly active reactive mediums of zirconia-supported Ni-ferrites (NiFe2O4/m-ZrO2 and NiFe2O4/c-YSZ) and unsupported NiFe2O4. Copyright (C) 2013, Hydrogen En ergy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2013.08.108

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  • Oxygen-releasing step of nickel ferrite based on Rietveld analysis for thermochemical two-step water-splitting 査読

    Nobuyuki Gokon, Ken Kondo, Tsuyoshi Hatamachi, Mineo Sato, Tatsuya Kodama

    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY   38 ( 12 )   4935 - 4944   2013年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    We investigated the thermal reduction (T-R) of NiFe2O4, either supported by m-ZrO2 or unsupported, as the oxygen-releasing step of a solar thermochemical water splitting cycle based on a ferrite/wustite redox system, by performing the Rietveld analysis using powder X-ray diffraction. The solid materials obtained after the T-R step at 1300-1400 degrees C were subjected to Rietveld analysis. The amounts and chemical compositions of the wustite phase produced by the T-R step and the remaining ferrite phase were identified quantitatively. Chemical reaction formulas for the different T-R temperatures were determined from the results. Consistency for the chemical reactions of the thermal reduction was discussed and evaluated comparing the O2 amounts predicted by the chemical reaction formulas and measured experimentally by mass spectrometry. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2013.02.014

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  • CO 2 gasification of coal cokes using internally circulating fluidized bed reactor by concentrated Xe-light irradiation for solar gasification 査読

    Nobuyuki Gokon, Ryuta Ono, Tsuyoshi Hatamachi, Li Liuyun, Hee-Joon Kim, Tatsuya Kodama

    International Journal of Hydrogen Energy   37 ( 17 )   12128 - 12137   2012年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    For the solar thermochemical gasification of coal coke to produce CO + H 2 synthetic gas using concentrated solar radiation, a windowed reactor prototype is tested and demonstrated at laboratory scale for CO 2 gasification of coal coke using concentrated Xe light from a 3-kW th sun simulator. The reactor was designed to be combined with a solar reflective tower or beam-down optics. The results for gasification performance (CO production rate, carbon conversion, and light-to-chemical efficiency) are shown for various CO 2 flow rates and ratios. A kinetics analysis based on homogeneous and shrinking core models and the temperature distributions of the prototype particle bed are compared with those for a conventional fluidized bed reactor tested under the same Xe light irradiation and CO 2 flow-rate conditions. The effectiveness and potential impacts of internally circulating fluidized bed reactors for enhancing gasification performance levels and inducing consistently higher bed temperatures are discussed in this paper. © 2012 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2012.05.133

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  • 4-5-2 Na_2CO_3/MgO溶融塩ソーラーレシーバー反応管に関する研究(4-5 太陽熱発電・水素製造3,Session 4 新エネルギー)

    高橋 将吾, 栗田 慎二, 籏町 剛, 櫻井 篤, 郷右近 展之, 児玉 竜也

    日本エネルギー学会大会講演要旨集   21   232 - 233   2012年

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    記述言語:日本語   出版者・発行元:一般社団法人 日本エネルギー学会  

    DOI: 10.20550/jietaikaiyoushi.21.0_232

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  • Kinetics of methane reforming over Ru/γ-Al2O 3-catalyzed metallic foam at 650-900 °c for solar receiver-absorbers 査読

    Nobuyuki Gokon, Yuhei Yamawaki, Daisuke Nakazawa, Tatsuya Kodama

    International Journal of Hydrogen Energy   36 ( 1 )   203 - 215   2011年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    The kinetics of methane reforming over Ru/γ-Al2O 3-catalyzed high porosity Ni-Cr-Al foam were examined at temperatures of 650-900 °C in a quartz tubular reactor using an electric furnace. The kinetic data were analyzed by four different types of kinetic models based on the basic, Eley-Rideal, Langmuir-Hinshelwood, and stepwise mechanisms. Validation of the kinetic models was carried out by calculating the determination coefficient r2 between the predicted and the experimental results for each model. The absolute average deviation percentage (AAD%) between the predicted and the experimental results was also estimated for each model. The kinetic model based on the reversible stepwise mechanism provided the best prediction of the experimental reforming rates with an AAD value of 6% in the range 650-850 °C. © 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2010.09.042

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  • Comparison Studies of reactivity on nickel-ferrite and cerium-oxide redox materials for two-step thermochemical water splitting below 1400?C 査読

    Tatsuya Kodama, Nobuki Imaizumi, Nobuyuki Gokon, Tsuyoshi Hatamachi, Daiki Aoyagi, Ken Kondo

    2011 Energy Sustainability Conference & Fuel Cell Conference, Washington DC, USA, August 7-10, 2011.   2011年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)  

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  • Ni/MgO-Al2O3 and Ni-Mg-O catalyzed SiC foam absorbers for high temperature solar reforming of methane 査読

    Nobuyuki Gokon, Yuhei Yamawaki, Daisuke Nakazawa, Tatsuya Kodama

    International Journal of Hydrogen Energy   35 ( 14 )   7441 - 7453   2010年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Ni catalyst supported on MgO-Al2O3 (Ni/MgO-Al2O3) prepared from hydrotalcite, and Ni-Mg-O catalyst are studied in regard to their activity in the CO2 reforming of methane at high temperatures in order to develop a catalytically activated foam receiver-absorber for use in solar reforming. First, the activity of their powder catalysts is examined. Ni/MgO-Al2O3 powder catalyst exhibits a remarkable degree of high activity and thermal stability as compared with Ni-Mg-O powder catalyst. Secondly, a new type of catalytically activated ceramic foam absorber - Ni/MgO-Al2O3/SiC - and Ni-Mg-O catalyzed SiC foam absorber are prepared and their activity is evaluated using a laboratory-scale receiver-reactor with a transparent quartz window and a sun-simulator. The present Ni-based catalytic absorbers are more cost effective than conventional Rh/γ-Al2O3 catalyzed alumina and SiC foam absorbers and the alternative Ru/γ-Al2O3 catalyzed SiC foam absorbers. Ni/MgO-Al2O3 catalyzed SiC foam absorber, in particular, exhibits superior reforming performance that provides results comparable to that of Rh/γ-Al2O3 catalyzed alumina foam absorber under a high flux condition or at high temperatures above 1000 °C. Ni/MgO-Al2O3 catalyzed SiC foam absorber will be desirable for use in solar receiver-reactor systems to convert concentrated high solar fluxes to chemical fuels via endothermic natural-gas reforming at high temperatures. © 2010 Professor T. Nejat Veziroglu.

    DOI: 10.1016/j.ijhydene.2010.04.040

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  • Internally circulating fluidized bed reactor using m-ZrO2 supported NiFe2O4 particles for thermochemical two-step water splitting 査読

    Nobuyuki Gokon, Hiroki Yamamoto, Nobuyuki Kondo, Tatsuya Kodama

    Journal of Solar Energy Engineering, Transactions of the ASME   132 ( 2 )   0211021 - 02110210   2010年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    A windowed internally circulating fluidized bed reactor was tested using m-ZrO2-supported NiFe2O4 (NiFe 2O4/m-ZrO2) particles as redox material for thermochemical two-step water splitting to produce hydrogen from water. The internally circulating fluidized bed of (NiFe2O4 /m-ZrO2 particles is directly heated by solar-simulated Xe light irradiation through a transparent quartz window mounted on top of the reactor. A sun simulator with three Xe lamps at laboratory scale has been newly installed in our laboratory for testing the fluidized bed reactor. The input power of incident Xe light can be scaled up to 2.6 kWth. Temperature distributions within the fluidized bed are measured under concentrated Xe light irradiation with an input power of 2.6 kWth. Hydrogen productivity and reactivity for the fluidized bed of (NiFe2O4 /m-ZrO2 particles are examined using two different reactors under the N2 flow rate and flow ratio, which yield a higher bed temperature. The feasibility of successive two-step water splitting using the fluidized bed reactor is examined by switching from N2 gas flow in the thermal reduction step to a steam/N2 gas mixture in the water decomposition step. It is confirmed that hydrogen production takes place in the single fluidized bed reactor by successive two-step water splitting. © 2010 by ASME.

    DOI: 10.1115/1.4001154

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  • Molten-salt tubular absorber/reformer (MoSTAR) project: Reforming performance of reactor tubes during intermittent heating 査読

    Nobuyuki Gokon, Tatsuya Kodama, Tsuyoshi Hatamachi, Shingo Yamashita, Taebeom Seo

    ASME 2010 4th International Conference on Energy Sustainability, ES 2010   2   105 - 113   2010年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)  

    Reforming performances for the double-walled reactor tubes with Na 2CO3/MgO composite thermal storage was examined by an intermittent heating. The intermittent heating of the reactor tubes is composed of the heat-discharge (or cooling) mode and the subsequent heating mode. The heat-discharging mode simulates a fluctuating insolation for cloud passages. The heating mode simulates a heating of reactor due to concentrated solar radiation by using an electric furnace. The internal tube of the reactor was packed with the 2wt%Ru/Al2O3 catalyst balls while the thermal storage materials were filled in the annular region of the reactor tubes. The reactor was heated up to 920°C in the cylindrical electric furnace and the CH 4/CO2 mixture was fed into the internal catalyst tube at gas hourly space velocity (GHSV) of 12500 h-1. Through the cooling mode and the subsequent heating mode, temperature variations of reactor tubes, catalyst and composite material, H2/CO ratio variations of effluent gas from the reactor, higher heating value (HHV) power of reformed gas were respectively examined for the double-walled reactor tubes and a single-wall reactor tube without the thermal storage. © 2010 by ASME.

    DOI: 10.1115/ES2010-90114

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  • Coal coke gasification in a windowed solar chemical reactor for beam-down optics 査読

    Tatsuya Kodama, Nobuyuki Gokon, Shu-Ich Enomoto, Shouta Itoh, Tsuyoshi Hatamachi

    Journal of Solar Energy Engineering, Transactions of the ASME   132 ( 4 )   2010年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Solar thermochemical processes, such as solar gasification of coal, require the development of a high temperature solar reactor operating at temperatures above 1000°C. Direct solar energy absorption by reacting coal particles provides efficient heat transfer directly to the reaction site. In this work, a windowed reactor prototype designed for the beam-down optics was constructed at a laboratory scale and demonstrated for CO2 gasification of coal coke using concentrated visible light from a sun-simulator as the source of energy. Peak conversion of light energy to chemical fuel (CO) of 14% was obtained by irradiating a fluidized bed of 500-710 μm coal coke size fraction with a power input of about 1 kW and a CO2 flow-rate of 6.5 dm3 min-1 at normal conditions. © 2010 American Society of Mechanical Engineers.

    DOI: 10.1115/1.4002081

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  • Molten-Salt Tubular Absorber/Reformer "MoSTAR" Project: The Thermal Storage Media of Na2CO3-MgO Composite Materials 査読

    Tatsuya Kodama, Nobuyuki Gokon, Shin-Ichi Inuta, Shingo Yamashita, Taebeom Seo

    Journal of Solar Energy Engineering, Transactions of the ASME   131 ( 4 )   0410131 - 0410138   2009年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    The molten-salt tubular absorber/reformer (MoSTAR) project aims to develop a novel type of "double-walled" tubular absorber/reformer with molten-salt thermal storage at high temperature for use in solar natural-gas reforming and solar air receiver, and to demonstrate its performances on the sun with a 5 kWt dish-type solar concentrator. The new concept of double-walled reactor tubes is proposed for use in a solar reformer by Niigata University, Japan, and involves packing a molten/ceramic composite material in the annular region between the internal catalyst tube and the exterior solar absorberwall. This solar tubular absorber concept may be also applied to solar air receiver for solar thermal power generation. The MoSTAR project includes the development of molten-salt thermal storage media, the new design and the fabrication of absorber/ reformer with the double-walled absorber tubes, and finally the solar demonstration on the 5 kWt dish concentrator of Inha University in Korea. In this paper, thermal storage media of the series of Na2CO 3-MgO composite materials were tested in a double-walled reformer tube with a thermal storage capacity of about 0.3 kWh. The chemical reaction performances for dry reforming of methane during cooling or heat-discharge mode of the reactor tube were investigated using an electric furnace. The experimental results obtained under feed gas mixture of CH4/CO 2=1:3 at a residence time of 0.3 s and at 1atm showed that the single reactor tube with 90 wt % Na2CO3 /10 wt % MgO composite material successfully maintained a high methane conversion above 90% with about 0.9 kW reforming scale based on high heating value during 45 min of the heat-discharge mode. The chemical reaction performances of the reactor tube were investigated also for the solar-simulating operation mode. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage. Copyright © 2009 by ASME.

    DOI: 10.1115/1.3197840

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  • Double-walled reformer tubes using high-temperature thermal storage of molten-salt/MgO composite for solar cavity-type reformer 査読

    Nobuyuki Gokon, Shin-ichi Inuta, Shingo Yamashita, Tsuyoshi Hatamachi, Tatsuya Kodama

    International Journal of Hydrogen Energy   34 ( 17 )   7143 - 7154   2009年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Composite materials with alkali carbonate and magnesia have been examined for high-temperature thermal storage in solar tubular reformers. The concept of a double-walled reactor tube involves packing a molten-salt/ceramic composite material into the annular region between internal catalyst tube and exterior solar-absorber wall. In this paper, the shape and interior structure of the reactor tube are newly designed for use in solar cavity-type reformers using straight reactor tubes. Na2CO3, K2CO3, and Li2CO3 composite materials with magnesia were tested as thermal storage media for CO2 reforming of methane during cooling mode of the reactor tube at a laboratory scale. The efficiency of Na2CO3/MgO composite with various MgO contents was also estimated. Composite materials of Na2CO3 80-90 wt% and MgO 20-10 wt% were successfully delayed the cooling of the catalyst bed and sustained methane conversion at &gt
    90%. A solar cavity-type reformer consisting of multiple straight reactor tubes is expected to enable stable operation of the solar reforming process under fluctuating solar insolation during cloud passage. © 2009 International Association for Hydrogen Energy.

    DOI: 10.1016/j.ijhydene.2009.06.047

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  • Thermochemical two-step water splitting cycles by monoclinic ZrO2-supported NiFe2O4 and Fe3O4 powders and ceramic foam devices 査読

    Nobuyuki Gokon, Hiroko Murayama, Ayumi Nagasaki, Tatsuya Kodama

    SOLAR ENERGY   83 ( 4 )   527 - 537   2009年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    A thermochemical two-step water splitting cycle is examined for NiFe2O4 and Fe3O4 supported on monoclinic ZrO2 (NiFe2O4/m-ZrO2 and Fe3O4/m-ZrO2) in order to produce hydrogen from water at a high-temperature. The evolution of oxygen and hydrogen by m-ZrO2-supported ferrite powders was studied, and reproducible and stoichiometric oxygen/hydrogen productions were demonstrated through a repeatable two-step reaction. Subsequently, a ceramic foam device coated with NiFe2O4/m-ZrO2 powder was made and examined as a water splitting device by the direct irradiation of concentrated Xe-light in order to simulate solar radiation. The reaction mechanism of the two-step water splitting cycle is associated with the redox transition of ferrite/wustite on the surface of m-ZrO2. A hydrogen/oxygen ratio for these redox powder systems exhibited good reproducibility of approximately two throughout the repeated cycles. The foam device loaded NiFe2O4/m-ZrO2 powder was also successful with respect to hydrogen production through 10 repeated cycles. A ferrite conversion of 24-76% was obtained over an irradiation period of 30 min. (C) 2008 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.solener.2008.10.003

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  • Kinetics of CO2 reforming of methane by catalytically activated metallic foam absorber for solar receiver-reactors 査読

    Nobuyuki Gokon, Yusuke Osawa, Daisuke Nakazawa, Tatsuya Kodama

    International Journal of Hydrogen Energy   34 ( 4 )   1787 - 1800   2009年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Ni-Cr-Al metallic foam absorber with high porosity was catalytically activated using a Ru/γ-Al2O3 catalyst, and was subsequently tested with respect to CO2 reforming of methane in a small-scale volumetric receiver-reactor by using a sun-simulator. A chemical storage efficiency of 37% was obtained for a mean light flux of 325 kW m-2. Furthermore, the activity and the stability of the metallic foam absorber were compared with those of a SiC foam absorber activated with the same Ru/γ-Al2O3 catalyst for 50 h of light irradiation, and it was found that the metallic foam absorber has superior catalytic stability in comparison to the SiC form absorber. In addition, unlike ceramic foams such as SiC, metallic foams feature superior plasticity, which prevents the emergence of cracks caused by mechanical or thermal shock. The kinetics of CO2 reforming of methane over Ru/γ-Al2O3/metallic foams was also examined for temperatures of 600-750 °C using a quartz tube reactor and an electric furnace. The experiments were performed by varying the methane/CO2 ratios of 0.3-3.0. Moreover, the kinetic data were fitted to four different types of kinetic models, namely the Langmuir-Hinshelwood, Basic, Eley-Rideal, and Stepwise mechanisms. The kinetic model which provided the best prediction of the experimental reforming rates was the Langmuir-Hinshelwood mechanism for temperatures of 600-700 °C. © 2008 International Association for Hydrogen Energy.

    DOI: 10.1016/j.ijhydene.2008.12.018

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  • New solar water-splitting reactor with ferrite particles in an internally circulating fluidized bed 査読

    Nobuyuki Gokon, Shingo Takahashi, Hiroki Yamamoto, Tatsuya Kodama

    Journal of Solar Energy Engineering, Transactions of the ASME   131 ( 1 )   0110071 - 0110079   2009年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    The thermal reduction of metal oxides as part of a thermochemical two-step watersplitting cycle requires the development of a high-temperature solar reactor operating at 1000-1500°C. Direct solar energy absorption by metal-oxide particles provides direct efficient heat transfer to the reaction site. This paper describes the experimental results of a windowed small reactor using an internally circulating fluidized bed of reacting metaloxide particles under direct solar-simulated Xe-beam irradiation. Concentrated Xe-beam irradiation directly heats the internally circulating fluidized bed of metal-oxide particles. NiFe2O4 /m-ZrO2 (Ni-ferrite on zirconia support) particles are loaded as the working redox material and are thermally reduced by concentrated Xe-beam irradiation. In a separate step, the thermally reduced sample is oxidized back to Ni-ferrite with steam at 1000°C. The conversion efficiency of ferrite reached 44% (±1.0%), which was achieved using the reactor at 1 kW of incident Xe lamp power. The effects of preheating temperature and NiFe2O4 /m-ZrO2 particle size on the performance of the reactor for thermal reduction using an internally circulating fluidized bed were evaluated. Copyright © 2009 by ASME.

    DOI: 10.1115/1.3027511

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  • Monoclinic zirconia-supported Fe3O4 for the two-step water-splitting thermochemical cycle at high thermal reduction temperatures of 1400-1600 degrees C 査読

    Nobuyuki Gokon, Hiroko Murayama, Jun Umeda, Tsuyoshi Hatamachi, Tatsuya Kodama

    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY   34 ( 3 )   1208 - 1217   2009年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Two-step thermochemical water-splitting using monoclinic ZrO2-supported Fe3O4 (Fe3O4/m-ZrO2) for hydrogen production was examined at high thermal reduction temperatures of 1400-1600 degrees C. After thermal reduction of Fe3O4/m-ZrO2, the reduced sample was quenched in liquid nitrogen, and was subsequently subjected to the water-decomposition step at 1000 degrees C. Quenching of the solid sample was conducted for analysis of the chemical reactions, such as phase transitions, occurring at high-temperature. The hydrogen productivity of Fe3O4 on a m-ZrO2 support and the conversion of Fe3O4 to FeO were significantly enhanced with higher thermal reduction temperatures. The Fe3O4-to-FeO conversion reached 60% when the Fe3O4/m-ZrO2 was thermally reduced at 1600 degrees C. The phase transition of m-ZrO2 support to tetragonal ZrO2 (t-ZrO2) did not occur during the thermal reduction at 1400-1500 degrees C, but it did proceed slightly at 1600 degrees C. Fe ions from Fe3O4 did not enter the ZrO2 lattice during high-temperature thermal reduction. Thus, the Fe3O4 loaded on a m-ZrO2 support can continuously contribute as a Fe3O4-FeO redox reactant for thermochemical water-splitting at high-temperatures of 1400-1600 degrees C. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.ijhydene.2008.12.007

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  • Molten-salt tubular absorber/reformer (MoSTAR) project: Metal-plate-bridged double tube reactor 査読

    Tatsuya Kodama, Nobuyuki Gokon, Shin-Ichi Inuta, Shin-Go Yamashita, Tsuyoshi Hatamachi, Taebeom Seo

    Proceedings of the ASME 3rd International Conference on Energy Sustainability 2009, ES2009   2   451 - 457   2009年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)  

    The Molten-Salt Tubular Absorber/Reformer (MoSTAR) Project, which is jointly conducted by Niigata University, Japan, and Inha University, Korea, aims to develop a novel-type of "double-walled" tubular absorbers/reformers with molten-salt thermal storage at high temperature for use in solar natural-gas reforming and solar air receiver, and to demonstrate their performances on sun with a 5-kWt dish-type solar concentrator. The new concept of "double-walled" reactor tubes was proposed for use in a solar reformer by Niigata University, Japan, and involves packing a molten salt in the annular region between the internal catalyst tube and the exterior solar absorber tube of the double reactor tube. In this work, "metal-plate- bridged" double reactor tubes are newly proposed for use in a solar reformer. Two different sized reactor tubes are constructed, and tested on chemical reaction performance for dry reforming of methane during cooling or heat-discharge mode of the reactor tube using an electric furnace. The experimental results obtained under feed gas mixture of CH4/CO 2 = 1:3 at a residence time of 0.36 s and at 1 atm showed that the double reactor tube with the heat storage medium Na2CO3 in the annular region successfully sustained a high methane conversion above 90% with about 0.7-kW output power of the reformed gas based on HHV for 40 min of the heat-discharge mode. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage. Copyright © 2009 by ASME.

    DOI: 10.1115/ES2009-90230

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  • REACTIVITY OF IRON-CONTAINING YSZ FOR A TWO-STEP THERMOCHEMICAL WATER SPLITTING USING THERMAL REDUCTION TEMPERATURES OF 1400-1500 degrees C 査読

    Tatsuya Kodama, Eiji Hiraiwa, Nobuyuki Gokon

    ES2008: PROCEEDINGS OF THE 2ND INTERNATIONAL CONFERENCE ON ENERGY SUSTAINABILITY, VOL 2   361 - 369   2009年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER SOC MECHANICAL ENGINEERS  

    A thermochemical two-step water splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting solar energy into clean hydrogen in sunbelt regions. Fe3O4 supported on YSZ (Yttrium-Stabilized Zirconia) or Fe3O4/YSZ is a promising working material for the two-step water splitting cycle. In the water splitting cycle, an iron-containing YSZ or Fe2+-YSZ is formed by a high-temperature reaction between Fe3O4 and YSZ support at 1400 degrees C in an inert atmosphere. The Fe2+-YSZ reacts with steam and generate hydrogen at 1000 degrees C, to form Fe3+-YSZ that is re-activated by a thermal reduction ill a;separate step at 1400 degrees C under an inert atmosphere. In the present work, the thermal reduction was performed in a higher temperature range of 1400-1500 degrees C while the hydrolysis reaction was carried Out at 1000 degrees C. It was confirmed by XRD analysis that the cyclic redox reactions Occurred based on the same reaction mechanism when using a thermal reduction temperature between 1400 and 1500 degrees C. The conversions of Fe3O4 to Fe2+-YSZ were 20, 26 and 47% when the thermal reduction temperature were 1400, 1450, and 1500 degrees C respectively, indicating that the x values in the formed Fe2+-YSZ or Fex2+YyZr1-yO2-y/2+x, were 0.08, 0.11, and 0.19 respectively, where y = 0.15. The conversions of Fe2+-YSZ to Fe3+-YSZ ill the hydrolysis reaction (at 1000 degrees C), however, decreased from 90% to 60% when the thermal reduction temperature increased from 1400 to 1500 degrees C. As the results, the hydrogen production reactivity of Fe3O4 supported on YSZ increased from 5.6 x 10(-4) to 7.5 x 10(-4) g per gram of Fe3O4/YSZ for one cycle on the cycle average by elevated thermal reduction temperature from 1400 to 1500 degrees C.

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  • Ferrite-loaded ceramic foam devices prepared by spin-coating method for a solar two-step thermochemical cycle 査読

    Nobuyuki Gokon, Tatsuya Kodama, Ayumi Nagasaki, Ko-Ichi Sakai, Tsuyoshi Hatamachi

    Proceedings of the ASME 3rd International Conference on Energy Sustainability 2009, ES2009   2   439 - 449   2009年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)  

    A two-step water-splitting thermochemical cycle using redox working material of iron-based oxide (ferrite) particles has been developed for converting solar energy into hydrogen. The two-step thermochemical cycle for producing a solar hydrogen from water requires a development of a high temperature solar-specific receiver-reactor operating at 1000-1500°C. In the present work, ferrite-loaded ceramic foams with a high porosity (7 cells per linear inch) were prepared as a water splitting device by applying ferrite/zirconia particles on a MgO-partially stabilized Zirconia (MPSZ) ceramic foam. The water splitting foam device was prepared using a new method of spin coating. A spin coating method we newly employed that has advantages of shortening preparation period and reducing of the coating process in comparison to previous preparation method reported. The water-splitting foam devices, thus prepared, were examined on hydrogen productivity and reactivity through a two-step thermochemical cycle. NiFe2O4/m-ZrO 2/MPSZ and Fe3O4/c-YSZ/MPSZ foam devices were firstly tested for thermal reduction of ferrite using the laboratory scale receiver-reactor by a sun-simulator to simulate concentrated solar radiation. Subsequently, with another quartz reactor the light-irradiated device was reacted with steam by infrared furnace. As a result, it was possible to perform cyclic reactions over several times and to produce hydrogen through thermal-reduction at 1500°C and water-decomposition at 1100-1200°C. In further experiments, the NiFe2O4/m-ZrO2/MPSZ foam device was successfully demonstrated in a windowed single reactor for cyclic hydrogen production by solar-simulated Xe-beam irradiation with input power of 1 kW. The NiFe2O4/m-ZrO2/MPSZ foam device produced hydrogen of 70-190μmol per gram of device through 6 cycles and reached ferrite conversion of 60% at a maximum. Copyright © 2009 by ASME.

    DOI: 10.1115/ES2009-90172

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  • Kinetics of CO2 reforming of methane by catalytically activated metallic foam absorber for solar receiver-reactors

    Nobuyuki Gokon, Yusuke Osawa, Daisuke Nakazawa, Tsuyoshi Hatamachi, Tatsuya Kodama

    2008 Proceedings of the 2nd International Conference on Energy Sustainability, ES 2008   2   371 - 383   2009年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)  

    Ni-Cr-Al alloy foam absorber with high porosity was catalytically activated using a Ru/γ-Al2O3 catalyst, and was subsequently tested with respect to CO2 reforming of methane in a small-scale volumetric receiver-reactor by using a sun simulator. A chemical storage efficiency of about 40% was obtained for a mean light flux of 325 kWm -2. Furthermore, the activity and the stability of the metallic foam absorber were compared with those of a SiC foam absorber activated with the same RU/γ-A12O3 catalyst for 50 h of light irradiation, and it was found that the metallic foam absorber has superior catalytic stability in comparison to the SiC form absorber. In addition, unlike ceramic foams such as SiC., metallic foams feature superior plasticity, which prevents the emergence of cracks caused by mechanical or thermal shock. The kinetics of CO2 reforming of methane over metallic foam absorbers were also examined for temperatures of 600-750°C using a quartz tube reactor and an electric furnace. The experiments were performed by varying the methane/CO 2 ratios of 0.5-2.3. Moreover, the kinetic data were fitted to four different types of kinetic models, namely the Langmuir-Hinshelwood, Basic, Eley-Rideal, and Stepwise mechanisms. The kinetic model which provided the best prediction of the experimental reforming rates was the Langmuir-Hinshelwood mechanism. Copyright © 2008 by ASME.

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  • Thermochemical two-step water-splitting for hydrogen production using Fe-YSZ particles and a ceramic foam device 査読

    Nobuyuki Gokon, Tomoki Hasegawa, Shingo Takahashi, Tatsuya Kodama

    ENERGY   33 ( 9 )   1407 - 1416   2008年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Fe3O4 supported on cubic yttria-stabilized zirconia (Fe3O4/C-YSZ) is proposed as a promising redox material for the production of hydrogen from water via a thermochemical two-step water-splitting cycle. In this study, the evolution of oxygen and hydrogen during the cyclic reaction was examined using Fe3O4/C-YSZ particles in order to demonstrate reproducible and stoichometric oxygen/hydrogen production through a repeatable two-step reaction. Subsequently, a ceramic foam device coated with Fe3O4 and c-YSZ particles was prepared and examined as a thermochemical water-splitting device in a directly irradiated receiver/reactor hydrogen production system. The Fe3O4/C-YSZ system formed a Fe-containing YSZ (Fe-YSZ) by high-temperature reaction between Fe3O4 and the c-YSZ support at 1400 degrees C in an inert atmosphere. The reaction mechanism of the two-step water-splitting cycle is associated with the redox transition of Fe2+-Fe3+ ions in the c-YSZ lattice. The Fe-YSZ particles exhibit good reproducibility for reaction with a hydrogen/oxygen ratio of approximately 2.0 throughout repeated cycles. The foam device coated with Fe-YSZ particles was also successful for continual hydrogen production through 32 repeated cycles. A 20-27% ferrite conversion was obtained using 10.5 wt% Fe3O4 loading over an irradiation period of 60 min. (C) 2008 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.energy.2008.04.011

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  • Iron-containing yttria-stabilized zirconia system for two-step thermochemical water splitting 査読

    Nobuyuki Gokon, Takayuki Mizuno, Yumiko Nakamuro, Tatsuya Kodama

    Journal of Solar Energy Engineering, Transactions of the ASME   130 ( 1 )   0110181 - 0110186   2008年2月

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)  

    An iron-containing yttria-stabilized zirconia (YSZ) or Fe-YSZ was found to be a promising working redox material for the thermochemical two-step water-splitting cycle. The Fe-YSZ was formed by a high-temperature reaction between YSZ doped with more than 8 mol % Y2O3 and Fe 3O4 supported on the YSZ at 1400°C in an inert atmosphere. The formed Fe-YSZ reacted with steam to generate hydrogen at 1000°C. The oxidized Fe-YSZ was reactivated by a thermal reduction at 1400°C in an inert atmosphere. The alternative O2 and H 2 generations in the repeated two-step reactions and the X-ray diffraction and chemical analysis studies on the solid materials indicated that the two-step water splitting was associated with a redox transition between Fe2+-Fe3+ ions in the cubic YSZ lattice. Copyright © 2008 by ASME.

    DOI: 10.1115/1.2807197

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  • Thermochemical two-step water splitting by ZrO2-supported NixFe3-xO4 for solar hydrogen production 査読

    T. Kodama, N. Gokon, R. Yamamoto

    SOLAR ENERGY   82 ( 1 )   73 - 79   2008年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    A thermochemical two-step water-splitting cycle using a redox metal oxide was examined for Ni(II) ferrites or NixFe3-xO4 (0 &lt;= x &lt;= 1) for the purpose of converting solar high-temperature heat to hydrogen. The Ni(II) ferrite was decomposed to Ni-doped wustite (NiyFe1-yO) at 1400 degrees C under an inert atmosphere in the first thermal-reduction step of the cycle; it was then reoxidized with steam to generate hydrogen at 1000 degrees C in the second water-decomposition step. Although nondoped Fe3O4 powders formed a nonporous, dense mass of iron oxide by the fusion of FeO and its subsequent solidification after the thermal-reduction step, Ni(II)-ferrite powders were converted into a porous, soft mass after the step. This was probably because Ni doping in the FeO phase raised the melting point of wustite above 1400 degrees C. Supporting the Ni(II) ferrites on m-ZrO2 (monoclinic zirconia) alleviated the high-temperature sintering of iron oxide; as a result, the supported ferrites exhibited greater reactivity and assisted the repeatability of the cyclic water splitting process as compared to the unsupported ferrites. The reactivity increased with the doping value x, and was maximum at x = 1.0 in the NixFe3-xO4/m-ZrO2 system. (C) 2007 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.solener.2007.03.005

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  • O<sub>2</sub>-Bridged Multicopper(II) Complex in Zeolite for Catalytic Direct Photo-oxidation of Benzene to Diphenols 査読

    Ken-ichi Shimizu, Rei Maruyama, Tsuyoshi Hatamachi, Tatsuya Kodama

    The Journal of Physical Chemistry C   111 ( 17 )   6440 - 6446   2007年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    The photo-oxidation of benzene with hydrogen peroxide is catalytically promoted by copper(II)-exchanged BEA zeolite (Cu-BEA), resulting in the selective formation of diphenols. Analysis by UV-vis, Cu K-edge X-ray absorption fine structure (XAFS), and Raman spectroscopies are used to identify the active species in Cu-BEA treated with the reaction mixture or a H2O2 solution. The reaction of monomeric Cu(II) cations in BEA zeolite with H2O2 yields O-2-bridged multicopper(II) complexes, possibly the (mu-eta(2):eta(2)-peroxo)dicopper(II) species, which is characterized by the Cu-Cu distance of 3.24 angstrom, the UV-vis band around 370 nm, and the Raman band at 830 cm(-1). Extended XAFS, in situ UV-vis, and O-2 temperature programmed desorption results show that thermal desorption of the bridged O-2 on the multicopper(II) site results in the formation of monomeric Cu(II) cations. In situ UV-vis under photo-irradiation shows that the complex is photolabile in the presence of benzene. The effective wavelength range for the benzene hydroxylation (300-420 nm) is in the wavelength range of ligand-to-metal charge transfer bands of the complex, suggesting that the photo-excitation of the complex is involved in the important step of the selective benzene hydroxylation.

    DOI: 10.1021/jp065674w

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  • Solar tubular reformer with molten-salt thermal storage - Design modification of the reactor tube and testing 査読

    Tatsuya Kodama, Tsuyoshi Hatamachi, Daisuke Nakano, Youhei Igarashi, Nobuyuki Gokon

    Proceedings of the ASME International Solar Energy Conference   197 - 204   2007年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER SOC MECHANICAL ENGINEERS  

    For thermal storage in solar tubular reformers, high-temperature composite materials with alkali carbonate and magnesia have been examined. The new concept of "double-walled reactor tube" was previously proposed to use in solar tubular reformers, which involves storing the molten-salt/ceramic composite material in the annular regions between an internal catalyst tube and the exterior solar absorber wall. The shape and structure of the reactor tube can be modified to match with design of a solar tubular reformer. In this paper, the interior structure of the reactor tube has been modified for use in cavity-type reformers using straight reactor tubes. The Na2CO3, K2CO3 and Li2CO3 composite materials with magnesia were prepared, and tested on heat-discharge mode performances for CO2 reforming of methane in the modified reactor tube of a laboratory scale.

    DOI: 10.1115/ISEC2006-99062

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  • A two-step water splitting with ferrite particles and its new reactor concept using an internally circulating fludized-bed 査読

    Nobuyuki Gokon, Takayuki Mizuno, Shingo Takahashi, Tatsuya Kodama

    Proceedings of the ASME International Solar Energy Conference   205 - 214   2007年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER SOC MECHANICAL ENGINEERS  

    A thermochemical two-step water splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting and storing solar energy into a fuel in sunbelt regions. The ZrO2-supported ferrite (or the ferrite/ZrO2) powders exhibit superior performances on activity and repeatability of the cyclic reactions when compared to conventional unsupported ferrites. In the first step at 1400 degrees C under an inert atmosphere, ferrite on ZrO2 support is thermally decomposed to the reduced phase of wustite that is oxidized back to ferrite on ZrO2 with steam in a separate second step at 1000 degrees C. In this paper, a number of ZrO2-supporetd ferrites, Mn-, Mg-, Co-, Ni- and Co-Mn-ferrites, are examined on activity. The NiFe2O4/ZrO2 powder was found to have a greatest activity between them. This paper also describes a new concept of a windowed solar chemical reactor using an internally circulating fluidized bed of ferrite/ZrO2 particles. In this concept, concentrated solar radiation passes downwards through the transparent window and directly heats the internally circulating fluidized bed. The exploratory experimental studies on this reactor concept are carried out in a laboratory scale for the thermal decomposition of NiFe2O4/ZrO2 particle bed as part of two-step water splitting cycle.

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  • Reactive Fe-YSZ coated foam devices for solar two-step water splitting 査読

    Tatsuya Kodama, Tomoki Hasegawa, Ayumi Nagasaki, Nobuyuki Gokon

    PROCEEDINGS OF THE ENERGY SUSTAINABILITY CONFERENCE 2007   821 - 829   2007年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER SOC MECHANICAL ENGINEERS  

    A thermochemical two-step water splitting cycle using a redox system of iron-based oxides or ferrites is one of the promising processes for converting solar energy into clean hydrogen in sunbelt regions. An iron-containing YSZ (Yttrium-Stabilized Zirconia) or Fe-YSZ is a promising working redox material for the two-step water splitting cycle. The Fe2+-YSZ is formed by a high-temperature reaction between YSZ, and Fe3O4 supported on the YSZ at 1400 degrees C in an inert atmosphere. The Fe2+-YSZ reacts with steam and generate hydrogen at 1000-1100 degrees C, to form Fe3+-YSZ that is re-activated by a thermal reduction in a separate step at temperatures above 1400 degrees C under an inert atmosphere. In the present work, a ceramic foam coated with the Fe-YSZ particles is examined as the thermochemical water splitting device for use in a solar-directly-irradiated receiver/reactor system. The Fe-YSZ particles were coated on an Mg-partially-stabilized zirconia foam disk and the foam device was tested on the two-step water splitting cycle being performed alternately at temperatures between 1100 and 1400 degrees C. The foam device was irradiated by concentrated visible light from a sun-simulator at the peak flux density of 1000 kW/m(2) and the average flux density of 470 kW/m(2) in a N-2 gas stream, and then, was reacted with steam at 1100 degrees C while heating by an infrared furnace. Hydrogen successfully continued to be produced in the repeated cycles.

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  • Pillaring of high charge density synthetic micas (Na-4-mica and Na-3-mica) by intercalation of oxides nanoparticles 査読

    Ken-ichi Shimizu, Yumiko Nakamuro, Ryoji Yamanaka, Tsuyoshi Hatamachi, Tatsuya Kodama

    MICROPOROUS AND MESOPOROUS MATERIALS   95 ( 1-3 )   135 - 140   2006年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Porous metal oxides synthesized by pillaring the high charge density synthetic micas, Na-4-mica and Na-3-mica, were reported for the first time. The interlayer spaces of mica layers are pre-expanded with n-octylammonium cation, which are subsequently replaced by pillar precursors (iron polyhydroxy cation or Fe3+-deposited silica sols) to form intercalation compounds. Heating the precursors at 773 K resulted in the formation of Fe2O3 or Fe2O3-SiO2 pillared micas having a high surface area (57-130 m(2)/g), high porosity and good thermal stability. Characterization with XRD, TEM, and N-2 adsorption experiments suggests that the resultant pillared micas consist of fragmented pillared clay forming a "house-of-cards" structure. The acidic property of the pillared micas was tested by TPD of ammonia, and the result shows that pillaring of Na-4-mica with Fe2O3 or Fe2O3-SiO2 causes a significant increase in the acid amount. (c) 2006 Elsevier Inc. All rights reserved.

    DOI: 10.1016/j.micromeso.2006.05.015

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  • Double-walled reactor tube with molten salt thermal storage for solar tubular reformers 査読

    T Hatamachi, T Kodama, Y Isobe, D Nakano, N Gokon

    JOURNAL OF SOLAR ENERGY ENGINEERING-TRANSACTIONS OF THE ASME   128 ( 2 )   134 - 138   2006年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ASME-AMER SOC MECHANICAL ENG  

    This paper proposes a novel-type of "double-walled" reactor tube with molten-salt thermal storage at high temperatures for use in solar tubular reformers. The prototype reactor tube is demonstrated on the heat-discharge and chemical reaction performances during cooling mode of the reactor tube at laboratory scale. The Na2CO3 composite material with MgO ceramics was filled into the outer annulus of the double-walled reactor tube while the Ru-based catalyst particles were filled into the inner tube. The heat discharge form the molten Na2CO3 circumvented the rapid temperature change of the catalyst bed, which resulted in the alleviation of decrease in chemical conversion during cooling mode of the reactor tube. The application of the new reactor tribes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

    DOI: 10.1115/1.2183803

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  • Pillaring of Ruddlesden-Popper perovskite tantalates, H(2)ATa(2)O(7) (A = Sr or La-2/3), with n-alkylamines and oxide nanoparticles 査読

    KI Shimizu, S Itoh, T Hatamachi, Y Kitayama, T Kodama

    JOURNAL OF MATERIALS CHEMISTRY   16 ( 8 )   773 - 779   2006年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    The Ruddlesden-Popper-type layered perovskite tantalates, H(2)ATa(2)O(7) (A = Sr or La-2/3), were pillared with n-alkylamines and oxide nanoparticles for the first time. H2SrTa2O7 can accommodate n-alkylamines (carbon numbers = 4, 8, 12, 16) to form intercalation compounds. A linear relationship is observed between the interlayer distance and the number of carbon atoms in n-alkyl chains, indicating the formation of a bilayer of the n-alkylamines. Porous metal oxides were synthesized by pillaring the n-octylamine intercalated H(2)ATa(2)O(7) perovskites with Fe2O3 or Fe-Si mixed oxide (FeSi). These materials were well characterized by XRD, TEM, N-2 adsorption, and Fe K-edge XAFS (XANES and EXAFS). FeSi pillared H2SrTa2O7 and H2La2/3Ta2O7 have a high surface area (52 and 130 m(2) g(-1)) and microporosity. Fe2O3 pillared H2SrTa2O7 has a macroporous structure with a relatively low surface area (14 m(2) g(-1)). XAFS analysis reveals that the Fe species in FeSi pillared perovskites are tetrahedral Fe3+ species incorporated in a silica matrix or highly dispersed on silica particles, while those in the Fe2O3 pillared one are alpha-Fe2O3 nanoparticles. The acidic property is tested by temperature programmed desorption (TPD) of ammonia, and the result shows that pillaring increases the number of acid sites in perovskites.

    DOI: 10.1039/b514066h

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  • Ru/Ni-Mg-O catalyzed SiC-foam absorber for solar reforming receiver-reactor 査読

    Tatsuya Kodama, Takuya Moriyama, Takehiro Shimoyama, Nobuyuki Gokon

    Solar Engineering 2005   697 - 705   2006年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER SOC MECHANICAL ENGINEERS  

    High-temperature solar reforming of methane with CO2 is investigated using a directly solar-irradiated 2 absorber subjected to a solar mean flux level above 400 kWm(-2) (the peak flux of about 700 kWm(-2)). The new type of catalytically-activated ceramic foam absorber - an Ru/Ni-Mg-O catalyzed SiC foam absorber - was prepared and its activity was tested in a laboratory-scale volumetric receiver-reactor with a transparent (quartz) window by using a sun-simulator. Compared to conventional Rh/Al2O3 catalyzed SiC foam absorber, this new catalytic absorber is more cost-effective and is found to exhibit a superior reaction performance at the high solar flux or at high temperatures, especially above 950 degrees C. This new absorber will be applied in solar receiver-reactor systems for converting concentrated high solar fluxes to chemical fuels via endothermic natural-gas reforming at the high temperatures.

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  • Double-walled reactor tube with molten salt thermal storage for solar tubular reformers 査読

    T. Hatamachi, T. Kodama, Y. Isobe, D. Nakano, N. Goukon

    Solar Engineering 2005   691 - 695   2006年

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    記述言語:英語   掲載種別:研究論文(国際会議プロシーディングス)   出版者・発行元:AMER SOC MECHANICAL ENGINEERS  

    This paper proposes a novel type of "double-walled" reactor tube with molten-salt thermal storage at high temperatures for use in solar tubular reformers. The prototype reactor tube is demonstrated on the heat-discharge and chemical reaction performances during cooling mode of the reactor tube at laboratory scale. The Na2CO3 composite material with MgO ceramics was filled into the outer annulus of the double-walled reactor tube while the Ru-based catalyst particles were filled into the inner tube. The heat discharge form the molten Na2CO3 circumvented the rapid temperature change of the catalyst bed, which resulted in the alleviation of decrease in chemical conversion during cooling mode of the reactor tube. The application of the new reactor tubes to solar tubular reformers is expected to help realize stable operation of the solar reforming process under fluctuating insolation during a cloud passage.

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  • Photocatalytic water splitting on Ni-intercalated Ruddlesden-Popper tantalate H2La2/3Ta2O7

    K Shimizu, S Itoh, T Hatamachi, T Kodama, M Sato, K Toda

    CHEMISTRY OF MATERIALS   17 ( 20 )   5161 - 5166   2005年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    A series of Ruddlesden-Popper-type hydrous layered perovskites, A'(2)ATa(2)O(7) (A' = H or K, A = La-2/3 or Sr), were presented as novel catalysts for photocatalytic water splitting into H-2 and O-2 under UV irradiation. These hydrous perovskites showed higher activity than anhydrous perovskites (KTaO3, La1/3TaO3) for overall splitting of water. Results of photoluminescence spectroscopy and H-2 evolution from aqueous n-butylamine solution support the hypothesis that the high activity of the hydrous perovskites results from their hydrated layered structure, where the photogenerated electrons and holes can be effectively transferred to the intercalated substrates (H2O and n-butylamine). Addition of Ni cocatalyst to H2La2/3Ta2O7 via an ion-exchange reaction increased the activity, while Ni addition did not improve the activity of H2SrTa2O7. Ni K-edge EXAFS/XANES, UV-vis spectroscopy, and TEM results for Niloaded catalysts indicate that Ni2+ ions and small NiO clusters are intercalated into the layers of H2La2/3Ta2O7, while relatively large NiO particles at the external surface of the perovskite are the main Ni species in H2SrTa2O7. Thus, the highly dispersed Ni(II) species at the interlayer space are shown to act as effective sites for H-2 evolution in the photocatalytic water splitting.

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  • Acidic properties of sulfonic acid-functionalized FSM-16 mesoporous silica and its catalytic efficiency for acetalization of carbonyl compounds 査読

    K Shimizu, E Hayashi, T Hatamachi, T Kodama, T Higuchi, A Satsuma, Y Kitayama

    JOURNAL OF CATALYSIS   231 ( 1 )   131 - 138   2005年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ACADEMIC PRESS INC ELSEVIER SCIENCE  

    Propyl-sulfonic acid-functionalized FSM-16 mesoporous silica (SO3H-FSM) is prepared by a conventional post-modification method. For the acetalization of carbonyl compounds with ethylene glycol, SO3H-FSM shows a higher rate and 1,3-dioxolane yield than conventional heterogeneous solid acids such as zeolites, montmorillonite K10 clay, silica-alumina, and the sulfonic resin. SO3H-FSM is stable during the reaction, with no leaching and deactivation of sulfonic acid groups, and is reusable without loss of its activity. The acidity and hydrophilicity of SO3H-FSM are well characterized by the microcalorimetry of NH3 adsorption, NH3-TPD, and H2O-TPD, and the result is compared with those for various aluminosilicate zeolites (HZSM5, HBEA, HY) and K10 clay. It is found that NH3-TPD is not suitable for characterizing the acidity of SO3H-FSM, because the decomposition of SO3H groups on SO3H-FSM begins above 200 degrees C. An NH3 adsorption microcalorimetric experiment at 150 degrees C shows that, compared with HZSM5, SO3H-FSM has a smaller number of acid sites but has a similar number of strong acid sites with ammonia adsorption heat above 140 kJ mol(-1). Comparison of the structural properties and catalytic results shows that a large pore diameter and low hydrophilicity are required to obtain high activity. Bronsted acid sites with a relatively strong acid strength are more suitable for this reaction, but the high acid concentration is not indispensable. The high activity of SO3H-FSM should be caused by the presence of the strong Bronsted acid sites in the mesopore with a relatively low hydrophilicity, where both reactants can smoothly access the acid sites. (c) 2005 Elsevier Inc. All rights reserved.

    DOI: 10.1016/j.jcat.2005.01.017

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  • Michael reaction of beta-ketoesters with vinyl ketones by iron(III)-exchanged fluorotetrasilicic mica: catalytic and spectroscopic studies

    K Shimizu, M Miyagi, K Toshiki, T Hatamachi, T Kodama, Y Kitayama

    JOURNAL OF CATALYSIS   229 ( 2 )   470 - 479   2005年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ACADEMIC PRESS INC ELSEVIER SCIENCE  

    Michael reaction of beta-ketoesters with vinylketones at room temperature under solvent-free condition is investigated with various Fe(3+) catalysts, including FeCl(3) (.) 6H(2)O supported on various supports (Fe-mica, Fe-mont, Fe-SiO(2), Fe-Al(2)O(3), Fe-NaY) and homogeneous catalysts, FeCl(3) (.) 6H(2)O and Fe(NO(3))(3) (.) 9H(2)O. Fe(3+)-exchanged fluorotetrasilicic mica (Fe-mica) shows highest activity. Fe-mica exhibits almost quantitative yields of Michael adducts, high turnover numbers (TON = 1000), and a low level of Fe leaching. After simple workup procedures, Fe-rnica can be recycled without a loss in activity. The relationship between catalytic activity and the catalyst structure determined by XRD, UV-vis, and Fe K-edge XANES/EXAFS is discussed in terms of the effect of clay support on the structure and reactivity of Fe(3+) species. The Fe3+ cation, highly dispersed in the interlayer of clay (mica or mont) or on SiO(2), is more active than the cluster-like Fe(3+) oxide or hydroxide species in Fe-NaY and Fe-Al(2)O(3). UV vis and XAFS results for the catalysts treated with reactants suggest that, during the reaction, the FeCl(2)(O)(4) octahedral species in FeCl(3) (.) 6H(2)O or those on Fe-SiO(2) are converted to the beta-diketonato complexes with two beta-diketonato ligands, whereas in Fe-mica beta-diketonato complexes with one beta-diketonato ligand are formed. The formation of beta-diketonato complexes results in a slight lowering of the Fe oxidation number from 3+, probably as a result of the electron donation from the beta-diketonato ligand to Fe(3+) as a Lewis acid site. The lower numbers of beta-diketonato ligand coordinated with Fe(3+) in Fe-mica should result in a larger coordination strength for beta-diketonato ligand than that in Fe-SiO(2), which was confirmed by acetylacetone-TPD. Thus, the central carbon atom of the beta-diketonato ligand in Fe-mica is more reactive toward nucleophilic attack by the coordinated enone, leading to higher activity for the Michael reaction. (C) 2004 Elsevier Inc. All rights reserved.

    DOI: 10.1016/j.jcat.2004.11.030

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  • Degradation of hydrophobic organic pollutants by titania pillared fluorine mica as a substrate specific photocatalyst 査読

    K Shimizu, H Murayama, A Nagai, A Shimada, T Hatamachi, T Kodama, Y Kitayama

    APPLIED CATALYSIS B-ENVIRONMENTAL   55 ( 2 )   141 - 148   2005年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The photocatalytic degradation of a highly hydrophobic and stable organic pollutant, gamma-hexachlorocyclohexane (gamma-HCH), was performed in aqueous suspended mixture of TiO2-containing catalysts. Unlike most of the organic pollutants, gamma-HCH was very stable under the conventional photocatalytic condition with TiO2 (P25). Among various catalysts, TiO2 pillared fluorine mica (Ti-mica) showed highest activity. The effect of preparation method of Ti-mica was also examined. The hydrothermal treatment increased the crystallinity of anatase pillar of Ti-mica, though the treatment at high temperature resulted in a decrease in the surface area and an increase in the pore size. Consequently, Ti-mica treated at lowest temperature (373 K), Ti-mica-373, was the most effective photocatalyst. The catalytic activity of TiO2 and Ti-mica-373 was compared for 13 kinds of organic compounds with various hydrophobicity. Ti-mica-373 showed 5-66 times higher rate than TiO2 for the degradation of hydrophobic organic pollutants (alpha, beta, gamma and delta-HCH, trans- and cis-chlordane, DDE, DDD and DDT) of low concentration (10 ppb). In contrast, TiO2 Showed higher rate than Ti-mica-373 for the degradations of less hydrophobic compounds (benzonitrile, chlorobenzene, 4-chloroacetophenone and 4-chloronitrobenzene). Over TiO2-mica-373, organic compounds with higher log P-OW value, i.e. more hydrophobic compounds, were decomposed with higher rate. A positive effect of the fluorine mica support is suggested to be caused by the interaction of hydrophobic reactant with the hydrophobic interlayer surface of pillared-clay. (C) 2004 Elsevier B.V. All rights reserved.

    DOI: 10.1016/j.apcatb.2004.08.005

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  • Structural investigations of functionalized mesoporous silica-supported palladium catalyst for Heck and Suzuki coupling reactions 査読

    K Shimizu, S Koizumi, T Hatamachi, H Yoshida, S Komai, T Kodama, Y Kitayama

    JOURNAL OF CATALYSIS   228 ( 1 )   141 - 151   2004年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ACADEMIC PRESS INC ELSEVIER SCIENCE  

    FSM-16 mesoporous silica-supported mercaptopropylsiloxane Pd(II) complex, Pd-SH-FSM, has been shown to act as an active, stabile, and recyclable heterogeneous catalyst for the Heck reaction of 4-bromoacetophenone with ethyl acrylate and for the Suzuki reaction of 4-bromoanisole with phenylboronic acid. The structure of the Pd species in Pd-SH-FSM before and after the reaction was well characterized by a combination of XRD, TEM, UV-vis, Pd K-edge XANES/EXAFS, and Pd L-III-edge XANES, and the results were compared with those of a amorphous silica-supported mercaptopropylsiloxane Pd(II) complex (Pd-SH-SiO2), unmodified FSM-16-supported Pd(OAc)(2) (Pd-FSM), and previously reported heterogeneous catalysts (Pd zeolite and Pd/C). The aggregation behavior of Pd species during the reaction greatly depends on the support. On Pd-SH-FSM after Heck and Suzuki reactions, Pd(II) species coordinated to the sulfur ligands were the main Pd species together with small Pd clusters as minor species, and the catalyst was reused without marked loss in the activity. On Pd-SH-SiO2, relatively large numbers of the Pd(II) species were converted to Pd clusters after the Suzuki reaction. On ligandless Pd-FSM, most of the Pd was aggregated to form Pd metal particles. The activity order of the recycled catalysts (Pd-SH-FSM &gt; Pd-SH-SiO2 &gt; Pd-FSM) indicates that the Pd(II) complexes on the sulfur ligands and possibly the small Pd clusters are more active than Pd metal particles. It is concluded that the sulfur ligands in the size-restricted mesopore are effective for preventing the aggregation of coordinated Pd complexes, and this results in high durability and recycling characteristic of the Pd-SH-FSM. The deactivation of the Pd complex via Pd aggregation was significant for the conventional Pd catalysts; [Pd(NH3)(4)](2+) complexes in Pd zeolite and PdO nanoclusters on Pd/C were changed to less reactive metal particles or clusters after Heck and Suzuki reactions. (C) 2004 Elsevier Inc. All rights reserved.

    DOI: 10.1016/j.jcat.2004.09.005

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  • Pd-sepiolite catalyst for Suzuki coupling reaction in water: Structural and catalytic investigations 査読

    K Shimizu, R Maruyama, S Komai, T Kodama, Y Kitayama

    JOURNAL OF CATALYSIS   227 ( 1 )   202 - 209   2004年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ACADEMIC PRESS INC ELSEVIER SCIENCE  

    [Pd(NH3)(4)](2+)-exchanged sepiolite clay (Pd-sepiolite) has been applied to the catalytic Suzuki-type carbon-carbon coupling reactions of 4-bromophenol with phenylboronic acid or sodium tetraphenylborate in water. The Pd-sepiolite effectively catalyzed the reaction under mild reaction conditions (at room temperature in air). The Pd-sepiolite system exhibits higher yield than unsupported Pd(II) salts, [Pd(NH3)(4)]Cl-2-impregnated SiO2 (Pd-SiO2), and a commercially available Pd/C consisting of Pd metal particles. The structure of Pd species in the catalysts before and after the reaction was well characterized by a combination of XRD, TEM, UV-Vis, Pd K -edge XANES/EXAFS, and Pd L-III-edge XANES. XAFS and TEM results confirmed the formation of metal particles after the reaction by unsupported Pd(II) salt and Pd-SiO2. In contrast, for Pd-sepiolite the change in the structure of Pd species after the reaction was not significant; the highly dispersed Pd(II) complex, present before the reaction, was still the main Pd species together with the small Pd clusters (2-7 nm) as minor species. As a result of the high stability, Pd-sepiolite was reused without losing its activity. Significantly high turnover numbers (TON = 940,000) were also attained at reflux temperature. It is suggested that Pd metal precipitation during the reaction is inhibited by a strong electrostatic interaction of sepiolite with Pd(II) species. (C) 2004 Elsevier Inc. All rights reserved.

    DOI: 10.1016/j.jcat.2004.07.012

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  • Selective photo-oxidation of benzene over transition metal-exchanged BEA zeolite 査読

    K Shimizu, H Akahane, T Kodama, Y Kitayama

    APPLIED CATALYSIS A-GENERAL   269 ( 1-2 )   75 - 80   2004年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Selective photo-oxidation of liquid benzene was studied using cation-exchanged zeolites dispersed in C6H6/CH3CN/H2O mixture at room temperature by using molecular oxygen. Screening with BEA zeolites exchanged with I I kinds of transition metal cations was performed. Pd2+-, Fe3+- and Cu-2(+)-BEA were shown to be effective for the formation of phenols (hydroquinone, resorcinol, catechol and phenol). The dihydroxybenzenes were mainly produced on Pd2+-, Fe3+- and Cu2+-BEA, while phenol and CO2 were the main products on TiO2 semiconductor (Degussa P25). The photocatalytic property was greatly changed by immobilization of Pd2+ on BEA; Pd2+-BEA showed higher activity and selectivity for the formation of phenols than [Pd(NH3)(4)]Cl-2 in homogeneous solution, on which unselective photo-oxidation of benzene to CO2 was the main reaction. The turnover number of Pd2+-BEA for the formation of phenols was 35 (based on Pd) in 24 h, indicating that the reaction proceeded catalytically. (C) 2004 Elsevier B.V All rights reserved.

    DOI: 10.1016/j.apcata.2004.04.001

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  • Ultrafine na-4-mica: Uptake of alkali and alkaline earth metal cations by ion exchange

    T Kodama, M Ueda, Y Nakamuro, K Shimizu, S Komarneni

    LANGMUIR   20 ( 12 )   4920 - 4925   2004年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    The cation exchange properties of alkali and alkaline earth metal cations at room temperature were investigated on an ultrafine, highly charged Na-4-mica (with the ideal mica composition Na4Mg6Al4Si4O20F4.xH(2)O). Ultrafine mica crystallites of 200 nm in size led to faster Sr2+ uptake kinetics in comparison to larger mica crystallites. The alkali metal ion (K+, Cs+, and Li+) exchange uptake was rapid, and complete exchange occurred within 30 min. For the alkaline earth metal ions Ba2+, Ca2+, and Mg2+, however, the exchange uptake required lengthy periods from 3 days to 4 weeks to be completed, similar to its Sr uptake, as previously reported. Kinetic models of the modified Freundlich and parabolic diffusion were examined for the experimental data on the Ba2+, Ca2+, and Mg2+ uptakes. The modified Freundlich model described well the Ba2+ ion uptake kinetics as well as that for the Sr2+ ion, while for the Ca2+ and Mg2+ ions the parabolic diffusion model showed better fitting. The alkali and alkaline earth ion exchange isotherms were also determined in comparison to the Sr2+ exchange isotherm. The thermodynamic equilibria for these cations were compared by using Kielland plots evaluated from the isotherms.

    DOI: 10.1021/la0362573

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  • SO3H-functionalized silica for acetalization of carbonyl compounds with methanol and tetrahydropyranylation of alcohols

    K Shimizu, E Hayashi, T Hatamachi, T Kodama, Y Kitayama

    TETRAHEDRON LETTERS   45 ( 26 )   5135 - 5138   2004年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Sulfonic acid group-functionalized amorphous silica acts as a highly effective and reusable catalyst for acetalization of various carbonyl compounds with methanol and tetrahydropyranylation of alcohols. (C) 2004 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.tetlet.2004.04.186

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  • Solar methane reforming using a new type of catalytically-activated metallic foam absorber 査読

    T Kodama, A Kiyama, T Moriyama, O Mizuno

    JOURNAL OF SOLAR ENERGY ENGINEERING-TRANSACTIONS OF THE ASME   126 ( 2 )   808 - 811   2004年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ASME-AMER SOC MECHANICAL ENG  

    The solar reforming of methane with CO2 is investigated using a direct irradiated absorber subjected to solar flux levels in the range 180-250 kWm(-2). This solar thermochemical process can upgrade the calorific value of the methane feed by 17% to produce hydrogen via the water-gas shift reaction. The volumetric receiver-reactor is best suited for this application because of its compactness and low thermal capacity. The new type of catalytically-activated "metallic foam" absorber-an Ni-Cr-Al-foam absorber applied with Ru/Al2O3-was found to have a superior thermal performance at relatively low solar fluxes when compared to conventional ceramic foam absorbers.

    DOI: 10.1115/1.1688382

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  • Ni/ceramic/molten-salt composite catalyst with high-temperature thermal storage for use in solar reforming processes 査読

    T Kodama, Y Isobe, Y Kondoh, S Yamaguchi, KI Shimizu

    ENERGY   29 ( 5-6 )   895 - 903   2004年4月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Composite materials of catalytically activated porous ceramics with molten salts were proposed for use in solar thermochemical reforming processes of methane as catalyst with high-temperature thermal storage. The high heat capacity and large latent heat (heat of solidification) of the composite molten salt at high temperatures are expected to circumvent the rapid temperature change of the catalyst bed under fluctuation of insolation. The composite catalysts of Ni-activated porous ceramics (mm-sized alumina or zirconia balls) with an alkali-metal chloride or carbonate (NaCl or Na2CO3) were prepared and examined for the activity and stability for CO2 reforming of methane. (C) 2003 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/S0360-5442(03)00194-4

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  • Photocatalytic water splitting on hydrated layered perovskite tantalate A(2)SrTa(2)O(7)center dot nH(2)O ( A = H, K, and Rb) 査読

    K Shimizu, Y Tsuji, T Hatamachi, K Toda, T Kodama, M Sato, Y Kitayama

    PHYSICAL CHEMISTRY CHEMICAL PHYSICS   6 ( 5 )   1064 - 1069   2004年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    A series of layered perovskite tantalates, A(2)SrTa(2)O(7) (A=H, Li, K, and Rb), were prepared as novel photocatalysts for photocatalytic water splitting into H-2 and O-2 under UV irradiation. The layered perovskite tantalates with hydrated interlayer space, A(2)SrTa(2)O(7).nH(2)O (A=H, K, and Rb), showed higher H-2 formation rate than anhydrous layered tantalate, Li2SrTa2O7, and anhydrous perovskite tantalate, KTaO3. H2SrTa2O7.nH(2)O and K2SrTa2O7.nH(2)O showed high activity for overall splitting of water without loading co-catalysts. The reaction over H2SrTa2O7.nH(2)O proceeded steadily more than 70 h, demonstrating a high durability of the catalyst. Effects of hydrated interlayer space on the catalytic activity were discussed on the basis of the results of photoluminescence spectra and the hydrogen evolution from aqueous solution of n-butylamine as a test reaction. The results indicate that the availability of interlayer space of layered tantalate as reaction sites is an important factor to improve the photocatalytic activity of Ta-based semiconductor materials.

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  • Alkaline earth cation exchange with novel Na-3-mica: kinetics and thermodynamic selectivities

    K Shimizu, K Hasegawa, Y Nakamuro, T Kodama, S Komarneni

    JOURNAL OF MATERIALS CHEMISTRY   14 ( 6 )   1031 - 1035   2004年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    The cation-exchange kinetics and thermodynamic equilibria for alkaline-earth metals by Na-3-mica[chemical composition of Na-2.94(Mg5.55Ti0.07Fe0.04)(oct)(Al2.07Si5.83)(tet)O20F4.1.72H(2)O] with a high layer charge were investigated at room temperature. The Ba, Sr, Ca and Mg uptake kinetics were determined and first-order, modified Freundlich, parabolic diffusion and Elovich kinetic models were examined for the experimental data. The first-order model gave a relatively good fit throughout for these cations and indicated a kinetic selectivity order of Ca2+&lt;Mg2+&lt;Sr2+&lt;Ba2+. The cation exchange isotherms for Ba, Sr, Ca and Mg uptakes with the Na-3-mica were also determined. The Kielland plots evaluated from the cation exchange isotherms showed a thermodynamic selectivity order of Ba2+&MGT;Sr2+&MGT;Ca2+&MGT;Mg2+. The above basic studies on the selective cation exchange of the highly charged ion exchanger are of relevance in the separation, immobilization and disposal of Sr-90 from aqueous nuclear wastes.

    DOI: 10.1039/b314013j

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  • Fe3+-exchanged fluorotetrasilicic mica as an active and reusable catalyst for Michael reaction

    K Shimizu, M Miyagi, T Kan-no, T Kodama, Y Kitayama

    TETRAHEDRON LETTERS   44 ( 40 )   7421 - 7424   2003年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Fe3+-exchanged fluorotetrasilicic mica acts as a highly effective and reusable catalyst for the solventless Michael reaction of beta-ketoesters with vinyl ketones under mild condition. The immobilized catalyst shows higher activity than homogeneous Fe3+ catalysts, FeCl(3)(.)6H(2)O and Fe(NO3)(3)(.)9H(2)O. (C) 2003 Elsevier Ltd. All rights reserved.

    DOI: 10.1016/j.tetlet.2003.08.048

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  • Stepwise production of CO-rich syngas and hydrogen via methane reforming by a WO3-redox catalyst 査読

    T. Kodama, T. Shimizu, T. Satoh, K.-I. Shimizu

    Energy   28 ( 11 )   1055 - 1068   2003年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Elsevier BV  

    DOI: 10.1016/s0360-5442(03)00093-8

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  • Ni−Mg−O Catalyst Driven by Direct Light Irradiation for Catalytically-Activated Foam Absorber in a Solar Reforming Receiver-Reactor 査読

    T. Kodama, A. Kiyama, T. Moriyama, T. Yokoyama, K-I. Shimizu, H. Andou, N. Satou

    Energy & Fuels   17 ( 4 )   914 - 921   2003年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/ef020270y

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  • Catalytic direct 1,4-conjugate addition of aldehydes to vinylketones on N-methyl-3-Aminopropylated FSM-16

    K Shimizu, H Suzuki, T Kodama, H Hagiwara, Y Kitayama

    SCIENCE AND TECHNOLOGY IN CATALYSIS 2002   145   145 - 148   2003年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:KODANSHA LTD  

    Direct 1,4-conjugate addition of naked aldehydes to vinylketones is catalysed effectively by N-metlyl-3-aminopropylated FSM-16 mesoporous silica. This reaction is regarded as a novel heterogeneous catalysis for a practical and environmentally friendly C-C bond formation reaction.

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  • Novel Na-3-mica: Alkaline earth cation exchange and immobilization

    T Kodama, K Hasegawa, K Shimizu, S Komarneni

    SEPARATION SCIENCE AND TECHNOLOGY   38 ( 3 )   679 - 694   2003年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:MARCEL DEKKER INC  

    The cation-exchange capacities for the alkaline earth metals Ba, Mg, and Ca, and their immobilization in the interlayers of a novel swelling fluorine mica (Na-3-mica) with a high-layer-charge density were studied. The mica was fully exchanged or saturated with Ba, Mg, and Ca ions and the cation-exchange capacities were determined to be 246, 338, and 322 meq(100 g)(-1), respectively, on anhydrous basis of mica. The chemical analyses of the saturated micas indicated that about three exchangeable interlayer sodium ions per unit cell existed in the mica as a result of the total negative layer charge due to both Mg vacancies in octahedral sheets and Al substitution in tetrahedral Si sheets of the silicate. The Ba, Mg, and Ca leachabilities of the saturated micas were investigated in 0.5 M NaCl background solutions at room temperature and these were compared to the Sr leachability of the Sr-saturated mica. The degree of the cation immobilization in the interlayers increased in the order of Ca &lt; Sr &lt; Ba &lt; Mg. This could be explained by the interlayer spacings and structures of the saturated micas.

    DOI: 10.1081/SS-120016659

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  • Self-aldol condensation of unmodified aldehydes secondary-amine immobilised in FSM-16 catalysed by silica

    K Shimizu, E Hayashi, T Inokuchi, T Kodama, H Hagiwara, Y Kitayama

    TETRAHEDRON LETTERS   43 ( 50 )   9073 - 9075   2002年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Self-aldol condensation of unmodified aldehydes was catalysed effectively by N-metlyl-3-aminopropylated FSM-16 mesoporous silica, whose activity was higher than that of homogeneous amine catalyst. (C) 2002 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0040-4039(02)02313-4

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  • Catalytically Activated Metal Foam Absorber for Light-to-Chemical Energy Conversion via Solar Reforming of Methane 査読

    T. Kodama, A. Kiyama, K.-I. Shimizu

    Energy &amp; Fuels   17 ( 1 )   13 - 17   2002年10月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:American Chemical Society (ACS)  

    DOI: 10.1021/ef0200525

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  • Metal-oxide-catalyzed CO2 gasification of coal using a solar furnace simulator. (vol 14, pg 1323, 2000)

    T Kodama, A Funatoh, T Shimizu, Y Kitayama

    ENERGY & FUELS   16 ( 3 )   802 - 802   2002年5月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    DOI: 10.1021/ef010289l

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  • Kinetics of metal oxide-catalyzed CO2 gasification of coal in a fluidized-bed reactor for solar thermochemical process. (vol 15, pg 1200, 2001)

    T Kodama, A Funatoh, K Shimizu, Y Kitayama

    ENERGY & FUELS   16 ( 3 )   802 - 802   2002年5月

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    記述言語:英語   出版者・発行元:AMER CHEMICAL SOC  

    DOI: 10.1021/ef0200018

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  • Stereoselective hydrogenation of linoleic acid over Ir/FSM-16 catalyst

    Ken-ichi Shimizu, Toshiki Kan-no, Tsuyoshi Hatamachi, Shin-ichi Komai, Tatsuya Kodama, Yoshie Kitayama

    Applied Catalysis A: General   228 ( 1-2 )   75 - 82   2002年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Ir/FSM-16 catalysts, prepared by the impregnation method, were investigated in the selective hydrogenation of linoleic acid (cis-9, cis-12 18:2). The results of various characterizations (X-ray diffraction (XRD), transmission electron microscopy (TEM), N2 sorption and X-ray photoelectron spectra (XPS)) indicated that Ir/FSM-16 catalysts contain Ir particles located to a large extent within the FSM-16 channels. For the catalytic hydrogenation of linoleic acid, the Ir/FSM-16 catalyst with relatively higher Ir loading (20 wt.%) produced cis-monoenoic acids (cis 18:1), while dienoic isomers mostly with trans configuration were predominantly produced over Ir supported on non-porous SiO2. The cis/trans ratio of monoenoic acids for the former catalyst was four times larger than that for the latter catalysts. The observed stereoselectivity may be due to an inhibition of the geometric isomerization by the limited space between Ir particles and pore wall of FSM-16. © 2002 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0926-860X(01)00954-1

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  • Synthesis of titania pillared mica in aqueous solution of acetic acid

    T Kaneko, M Fujii, T Kodama, Y Kitayama

    JOURNAL OF POROUS MATERIALS   8 ( 2 )   99 - 109   2001年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:KLUWER ACADEMIC PUBL  

    The preparation of TiO2-pillared mica was carried out in a CH3COOH aqueous solution. Titanium ion species were obtained by an addition of Ti(C3H7O4 to an aqueous solution of CH3COOH and by subsequent aging of the solution for a prescribed time followed by intercalation of these ionic species into the interlayers of mica. Ti4+-intercalated mica was thus obtained by ion exchange. After the sample was calcined at 773 K in air, TiO2-pillared mica was produced. The pillaring of TiO2 in the interlayer of mica was confirmed by XPS. The surface area TiO2-pillared mica was about 100 times larger than that of mica alone. The basal spacings of the products heated above 523 K were in the range from 2.01 nm to 2.68 nm in the samples obtained under various conditions.

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  • Thermochemical conversion of CH4 to C-2-hydrocarbons and H-2 over SnO2/Fe3O4/SiO2 in methane - Water co-feed system

    T Shimizu, Y Kitayama, T Kodama

    ENERGY & FUELS   15 ( 2 )   463 - 469   2001年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Highly endothermic conversion of methane to C-2-hydrocarbons and hydrogen was catalytically demonstrated over the SnO2/Fe3O4/SiO2 at 1173 K under co-feeding of methane and steam. The main products were C2H4, C2H6, CO, CO2, and hydrogen. At a low W/F value (a high GHSV), methane was selectively converted to C-2-hydrocarbons and hydrogen, while at a high W/F value (a low GHSV), steam reforming of methane to produce CO and hydrogen became dominant. At the GHSV = 4000-12000 h(-1), 87-94% of C-2 selectivity with 4-6% of methane conversion was obtained at the C-2-formation rate = 4-8 mmol-C h(-1) g(-1)-cat. This process offers the efficient conversion of natural gas to C-2-hydrocarbon and hydrogen utilizing high-temperature heat such as concentrated solar radiation below 1173 K.

    DOI: 10.1021/ef000200w

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  • CO2 reforming of methane in a molten carbonate salt bath for use in solar thermochemical processes

    T Kodama, T Koyanagi, T Shimizu, Y Kitayama

    ENERGY & FUELS   15 ( 1 )   60 - 65   2001年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    CO2 reforming of methane was studied by bubbling a CH4/CO2 mixture in a molten salt bath of alkali-metal carbonate mixture (Na2CO3/K2CO3) containing suspended metal catalyst powder at 1223 K, Ni, Fe, Cu, or W metals, supported on an Al2O3 support were examined for activity and selectivity. The most active and selective catalyst was the Ni/Al2O3 catalyst. The methane conversion increased with an increase in the W/F ratio (W = weight of the molten salt bath containing the Ni/Al2O3 catalyst, and F = flow rate of CH4/CO2 mixture). About 70% of methane conversion was obtained at a W/F ratio of 0.25 g min cm(-3), in which the H-2/CO ratio in the product gas was approximately the stoichiometric ratio of one. This technique will be applied to the solar thermochemical methane reforming for converting solar high-temperature heat to chemical fuels, to give stable operations under fluctuation of insolation and thermal uniformity in the solar reformer under concentrated solar irradiation.

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  • Thermochemical methane reforming using WO3 as an oxidant below 1173 K by a solar furnace simulator

    T Shimizu, K Shimizu, Y Kitayama, T Kodama

    SOLAR ENERGY   71 ( 5 )   315 - 324   2001年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Thermochemical methane reforming by a reactive redox system of WO, was demonstrated under direct irradiation of the metal oxide by a concentrated, solar-simulated Xe-lamp beam below 1173 K, for the purpose of converting solar high-temperature heat to chemical fuels. In the proposed cycling redox process, the metal oxide is expected to react with methane as an oxidant to produce syngas with a H-2/CO ratio of two, which is suitable for the production of methanol, and the reduced metal oxide which is oxidized back with steam in a separate step to generate hydrogen uncontaminated with carbon oxide. The ZrO2-supported WO3 gave about 45% of CO yield and 55% of H-2 yield with a H-2/CO ratio of about 2.4 in a temperature range of 1080-1160 K at a W/F ratio of 0.167 g min Ncm(-3) (W is the weight of WO3 phase and F is the flow rate of CHO. The activity data under the solar simulation were compared to those for the WO3/ZrO2 heated by irradiation of an infrared light. This comparison indicated that the CO selectivity was much improved to 76-85% in the solar-simulated methane reforming, probably by photochemical effect due to WO, phase. The main solid product of WO2 in the reduced WO3/ZrO2 was reoxidized to WO3 with steam to generate hydrogen below 1173 K. (C) 2001 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0038-092X(01)00058-5

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  • Synthesis of Na-2-mica from metakaolin and its cation exchange properties

    T Kodama, T Higuchi, T Shimizu, K Shimizu, S Komarneni, W Hoffbauer, H Schneider

    JOURNAL OF MATERIALS CHEMISTRY   11 ( 8 )   2072 - 2077   2001年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    Na-2-mica of the ideal composition of Na2Mg6Al2Si6O20F4. xH(2)O was prepared from a mixture of NaF, magnesium nitrate, SiO2 and calcined kaolinite (the latter serving as a cost-effective aluminosilicate source) at 800 degreesC and was found to excel in Sr removal from solutions at room temperature. This mica was characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and Al-27 and Si-29 magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. Fundamental studies of nNa(+) --&gt; Mn+ (Mn+ = Sr2+, Ca2+, Li+, K+ and Cs+) equilibria revealed a high selectivity and large capacity for Sr2+ ion uptake. A relatively low-temperature heat treatment (200 degreesC) of the Sr-exchanged mica resulted in collapse of the hydrated interlayer spacings of the mica, which will be useful to immobilize strontium in the stable unhydrated phase. This selective Sr-ion exchanger is expected to be useful for Sr-90 removal and its immobilization.

    DOI: 10.1039/b101186n

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  • Crystal-size control and characterization of Na-4-mica prepared from kaolinite

    T Kodama, Y Harada, M Ueda, K Shimizu, K Shuto, S Komarneni, W Hoffbauer, H Schneider

    JOURNAL OF MATERIALS CHEMISTRY   11 ( 4 )   1222 - 1227   2001年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    A simple and economical method for the synthesis of high-charge-density Na-4-mica (ideal chemical composition of Na4Mg6Al4Si4O20F4. xH(2)O) from kaolinite was investigated. Synthesis conditions were varied to control crystal size. This novel swelling Na-4-mica was synthesized from a mixture of kaolinite, magnesium nitrate (or ultrafine MgO) and NaF at 850 degreesC, and characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), particle size analysis by laser diffraction and Al-27 and Si-29 magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy. Decreasing the mass of NaF flux during the crystallization of Na-4-mica reduced the crystallite size from 2 to 0.2 mum. As the crystallite size decreased, the average particle size of the mica decreased from 5 to 2 mum. Al-27 MAS-NMR spectra showed that all or nearly all Al is in tetrahedral coordination whereas Si-29 MAS-NMR spectra showed that the nearest neighbour environment of Si is mainly in Si(3Al), as expected based on the Si:Al ratio.

    DOI: 10.1039/b009418h

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  • Metal-oxide-catalyzed CO2 gasification of coal using a solar furnace

    T Kodama, A Funatoh, T Shimizu, Y Kitayama

    ENERGY & FUELS   14 ( 6 )   1323 - 1330   2000年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    Metal-oxide-catalyzed CO2 gasification of coal was demonstrated in small packed-bed and fluidized-bed reactors using a solar furnace simulator, for the purpose of converting solar high-temperature heat to chemical fuels. The catalytic activities of In2O3 and ZnO were investigated because used In2O3 or ZnO catalyst may be separated from remaining coal ash by In2O or Zn evaporation at high temperatures and at a reducing atmosphere. Bituminous coal with or without the metal-oxide catalyst in the quartz-tube reactor was directly irradiated by the concentrated Xe-lamp beam and CO2 was fed to the reactor at pCO(2) = 1.0. In the packed-bed reactor, In2O3 and ZnO much improved the chemical coal conversion by about 4-5 and 2-3 times at the catalyst loading of 17 wt %-In and 30 wt %-Zn in the coal-metal-oxide mixture, respectively, at temperatures around 1000-1400 K. In the fluidized-bed reactor at a small catalyst loading (8-10 wt %-metal in the coal-metal-oxide mixture) and at 1073-1163 K, In2O3 catalytically increased the coal-conversion rate by 3 times but ZnO scarcely showed the catalytic activity. This metal-catalyzed coal gasification process offers the efficient solar production of the syngas calorifically upgraded by solar energy.

    DOI: 10.1021/ef000169y

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  • Thermochemical methane reforming using a reactive WO3/W redox system

    T Kodama, H Ohtake, S Matsumoto, A Aoki, T Shimizu, Y Kitayama

    ENERGY   25 ( 5 )   411 - 425   2000年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    The methane reforming process combined with metal oxide reduction was evaluated, for the purpose of converting solar high-temperature heat to chemicals below 1273 K. The metal oxide was endothermically reacted with methane, to produce CO, hydrogen and the component metal in the temperature range of 1173-1273 K. Of the metal oxide candidates, WO3 and V2O5 were found to be reactive and selective metal oxides for the purposes of methane reforming. The metallic tungsten produced by methane reforming could be used to split water and to generate hydrogen at a lower temperature of 1073 K. To improve the reactivities of WO3 for methane reforming and the subsequent splitting of water, supported tungsten oxides were examined in the temperature range of 1073-1273 K. The reactivities were much improved with the ZrO2-supported WO3, giving a methane conversion of 70% and a CO selectivity of 86%. Our findings indicate the possibility that the proposed two-step process using a WO3/W redox system may be a potentially new thermochemical path that produces useful energy carriers of processed metal, syngas and methanol for storing and transporting solar energy from the sun belt to remote population centers. (C) 2000 Elsevier Science Ltd. All rights reserved.

    DOI: 10.1016/S0360-5442(99)00084-5

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  • Thermochemical CO2 gasification of coal using a reactive coal-In2O3 system

    T Kodama, A Aoki, H Ohtake, A Funatoh, T Shimizu, Y Kitayama

    ENERGY & FUELS   14 ( 1 )   202 - 211   2000年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    A number of coal-metal oxide systems were examined for a thermochemical CO2 gasification of coal in a two-step cyclic redox mode, as well as in a normal single-step mode for the purpose of utilizing solar high-temperature heat below 1173 K. In the two-step cyclic redox mode, metal oxide was reacted with coal powder as an oxidant in the absence of CO2 at 1173 K to produce CO, H-2, and the component metal which was reoxidized with CO2 to generate CO at lower temperatures in a separate step. In2O3 was found to be the most reactive metal oxide among the thermodynamically promising metal oxides. The two-step cyclic CO2 gasification could be repeated using the In2O3/In redox system by resupplying the consumed coal to the system. About 80% of the coal supplied to the system was gasified at the temperature range of 1023-1173 K. The In2O3 phase was completely regenerated without the formation of other solid phases after repeating the two-step gasification. In a normal single-step, continuous feeding mode of CO2 at a constant temperature of 1173 K, the coal-In2O3 system also showed the most reactivity for the Boudouard reaction of C + CO2 --&gt; 2CO in the CO2 gasification of coal at the metal content of 17 wt % in the coal and metal oxide mixture. Depending on the indium content in the mixture, the initial coal-conversion rates with the coal-In2O3 system were 2.5-4 times as fast as that in the coal-CO2 reaction without any catalysts. The separation of used In2O3 from the remaining coal ash by In2O evaporation was also proposed.

    DOI: 10.1021/ef990135u

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  • Simplified synthesis of Na-4-mica from kaolinite and its cation-exchange properties

    T Kodama, S Komarneni

    SEPARATION SCIENCE AND TECHNOLOGY   35 ( 8 )   1133 - 1152   2000年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:TAYLOR & FRANCIS INC  

    The synthetic process of a high-charge-density sodium fluorophlogopite mica, Na-4-mica (with an ideal chemical composition of Na4Mg6Al4Si4O20F4. nH(2)O), using kaolinite as a raw material, has been investigated with respect to developing a simplified procedure and controlling crystal size. A fine and highly crystalline phase of the hydrated Na-4-mica, which is essential for practical applications, could be easily prepared from a mixture of kaolinite (or metakaolin) and magnesium nitrate using NaF flux at temperatures below 800 degrees C. An increased mass of NaF flux in the simplified process at 800 degrees C yielded somewhat larger and well-dispersed Na-4-mica crystals with hexagonal and plate-like shapes of 2-3 mu m in size. Cation-exchange equilibria was studied for alkaline earth metal ions of Sr, Ba, and Ca, as well as transition metal ions of Cu and Pb, at room temperature using the hydrated Na-4-mica synthesized by the simplified process. The order of selectivity for the alkaline earth metal ions was Ba2+ &gt;&gt; Sr2+ &gt; Ca2+, and the cation-exchange capacities were 197, 83, and 77 mequiv (100 g)(-1), respectively.

    DOI: 10.1081/SS-100100216

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  • Na-4-mica: simplified synthesis from kaolinite, characterization and Zn, Cd, Pb, Cu and Ba uptake kinetics

    T Kodama, S Komarneni, W Hoffbauer, H Schneider

    JOURNAL OF MATERIALS CHEMISTRY   10 ( 7 )   1649 - 1653   2000年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    A swelling Na-4-mica of the brittle mica type (ideal chemical composition of Na4Mg6Al4Si4O20F4. xH(2)O) was prepared by a simplified one-step synthetic process from kaolinite at or below 800 degrees C. Hydrated and well-dispersed Na-4-mica particles of about 2 mu m in size were prepared at 800 degrees C. The Al-27 MAS-NMR spectrum of this mica showed that almost all Al was in tetrahedral coordination while the Si-29 MAS-NMR spectrum showed that the nearest neighbor environment of Si was mainly Si(3Al), as expected based on the Si : Al molar ratio of 1 : 1 in the Na-4-mica. The CEC of the mica was determined to be 447 mequiv (100 g)(-1). With this Na-4-mica, the Zn, Cd, Pb, Cu and Ba uptake kinetics were investigated in a 0.5 M NaCl background solution at room temperature and were found to be quite rapid.

    DOI: 10.1039/b000041h

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  • Cyclodehydration of diethylene glycol (DEG) catalyzed by clay mineral sepiolite

    Y Kitayama, M Kamimura, K Wakui, M Kanamori, T Kodama, J Abe

    JOURNAL OF MOLECULAR CATALYSIS A-CHEMICAL   142 ( 2 )   237 - 245   1999年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Clay mineral sepiolite exhibited high selectivity for the catalytic conversion of diethylene glycol (DEG) into 1,4-dioxane. The selectivity for the 1,4-dioxane formation depended on weight hourly space velocity (WHSV) and the tunnel structure of sepiolite. When an excess DEG was supplied over the adsorption capacity of the tunnels in sepiolite, the selectivity for 1,4-dioxane formation from DEG decreased and by-products formation increased. These results indicate that cyclodehydration of DEG takes place in the internal space of the intracrystalline tunnels of sepiolite and by-products formation occurs on the outer surface of sepiolite. The Mg(II) ion along the tunnel wall of sepiolite acts as an active site for the cyclodehydration. (C) 1999 Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S1381-1169(98)00290-8

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  • A reactive redox system of metal oxide for a two-step thermochemical cycle for converting coal to upgraded chemical fuels of CO/H-2

    T Kodama, T Shimizu, A Aoki, Y Kitayama

    JOURNAL DE PHYSIQUE IV   9 ( P3 )   343 - 348   1999年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:E D P SCIENCES  

    A two-step thermochemical process using a redox system of metal oxides for converting coal to CO and H-2 with H2O/CO2 was studied for the propose of utilizing solar high-temperature heat below 1173 K. In the first step, metal oxide was reacted with coal as an oxidant to produce CO and H-2: metal oxide + CHn(coal) --&gt; metal + xCO + (l-x)CO2 + n/2H(2). The metal so formed was reoxidized with H2O or CO2 to generate H-2 or CO in the second step. A number of coal-metal oxide systems were thermodynamically examined and demonstrated at 1173 K. The coal-In2O3 and coal-SnO systems yielded 82 and 62%, respectively. With iron-based oxides, the In(III)-, Ni(II)- and Sn(II)-doped ferrites yielded 60-70% of coal conversions. In these coal-ferrite systems, magnetic separation of recovered ferrite from coal ashes can be expected. The proposed two-step process using In(III)-ferrite could be repeated with highly coal conversion of 60-90%. Our two-step process is superior to the conversions of coal and H2O/CO2 to H-2 and CO below 1173 K by the direct single-step reactions, CHn + H2O --&gt; CO + (n/2+1)H-2 and CHn + CO2 --&gt; 2CO + n/2H(2).

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  • A two-step thermochemical conversion of CH4 to CO, H-2 and C-2-hydrocarbons below 1173 K

    A Aoki, T Shimizu, Y Kitayama, T Kodama

    JOURNAL DE PHYSIQUE IV   9 ( P3 )   337 - 342   1999年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:E D P SCIENCES  

    A high-temperature thermochemical process using a redox system of metal oxide is proposed for converting CH4 to CO, H-2, and C-2-hydrocarbons (C-2-HCs). Reactions were performed in a two-step redox cycle. In the first high-temperature and endothermic step, methane is reacted with metal oxide to produce C2-HCs and the reduced metal oxide:
    2CH(4)+ metal oxide --&gt; C2Hn + (4-n/2)H2O + reduced metal oxide
    In the second step, H2O or CO2 is reacted with the reduced metal oxide to generate H-2 or CO at lower temperatures:
    H2O + reduced metal oxide --&gt; H-2 + metal oxide
    CO2 + reduced metal oxide --&gt; CO + metal oxide
    The net reactions are 2CH(4) --&gt; C2H(n) + (4-n/2)H-2, and 2CH(4) + (4-n/2)CO2 --&gt; C2Hn + (4-n/2)(CO + H2O). A thermodynamic analysis showed that redox systems of Fe3O4/FeO, SnO2/SnO and WO3/WO2 are promising for the two-step process. The redox system of Fe3O4 was experimentally examined. Methane was selectively converted to C-2-HCs, H-2, and CO by the two-step process using the Sig-supported Fe3O4 (Fe3O4/SiO2) in the temperature range from 1123 to 1173 K. It was found that the high-temperature methane decomposition to bulk carbon was efficiently suppressed over Fe3O4/SiO2 This process offers the efficient endothermic net reaction for converting natural gas to C2H4, H-2, and CO with upgraded calorific values. utilizing concentrated solar radiation as the energy source of high-temperature process heat below 1173 K.

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  • Na-4-mica: Cd2+, Ni2+, Co2+, Mn2+ and Zn2+ ion exchange

    Tatsuya Kodama, Sridhar Komarneni

    Journal of Materials Chemistry   9 ( 2 )   533 - 539   1999年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    Selective cation exchange for divalent transition metals of Cd, Ni, Co, Mn and Zn has been investigated with the high-charge-density sodium fluorophlogopite mica, Na-4-mica. The Na-4-mica was easily and economically prepared by the crystallization from a mixture of NaF, MgO and metakaolin, the latter serves as an inexpensive aluminosilicate source. Ion exchange isotherms for Cd2+, Ni2+, Co2+, Mn2+ and Zn2+ were obtained at room temperature and the thermodynamic functions of the ion exchange equilibria were calculated. The 2Na+ → M2+ exchange with the Na-4-mica showed the following selectivity: Zn2+ &gt
    Ni2+ ≃Co2+ ≃Cd2+ &gt
    Mn2+. The interlayer structure of the hydrated Na-4-mica with the open interlayer space in the range 12.1-13.9 Å was retained during the ion-exchange reaction, indicating the possibility of the reversible 2Na+ ⇆M2+ exchange. The basic selective cation exchange studies of the high-charge-density ion exchanger are of relevance in recovery of metals from waste solution, and waste water treatment and disposal.

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  • Structure refinement of lithium ion conductors Li3Sc2(PO4)(3) and Li3-2x(Sc1-xMx)(2)(PO4)(3) (M = Ti, Zr) with x = 0.10 by neutron diffraction

    T Suzuki, K Yoshida, K Uematsu, T Kodama, K Toda, ZG Ye, M Ohashi, M Sato

    SOLID STATE IONICS   113   89 - 96   1998年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    The crystal structure of lithium ion conductors, Li3Sc2(PO4)(3) and Li3-2x(Sc1-xMx)(2)(PO4)(3) (M = Ti, Zr) with x = 0.10, were refined by Rietveld analysis for neutron diffraction patterns in order to confirm the site location and site occupancy for Li ions. The Rietveld refinement confirmed that a high disorder was introduced to three kinds of Li sites in the high temperature superionic conduction phase of Li3Sc2(PO4)(3). The high temperature phase was stabilized at room temperature by substituting Ti4+ or Zr4+ for Sc3+ sites. The stabilized materials were also found to have similar high disorder over the Li sites. (C) 1998 Published by Elsevier Science B.V. All rights reserved.

    DOI: 10.1016/S0167-2738(98)00279-3

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  • Efficient thermochemical cycle for CO2 gasification of coal using a redox system of reactive iron-based oxide

    T Kodama, A Aoki, T Shimizu, Y Kitayama, S Komarneni

    ENERGY & FUELS   12 ( 4 )   775 - 781   1998年7月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    A two-step thermochemical process using a redox system of metal oxides for converting coal and CO2 to CO was studied on a number of iron-based oxides (ferrites) for the purpose of utilizing solar high-temperature heat below 1173 K. In the first step, ferrite was reacted with coal powder as an oxidant to produce CO, CO2, and the component metals. Pure magnetite (Fe3O4) was readily reduced to FeO but the reduction from FeO to alpha-Fe scarcely proceeded in 30 min of the reaction with coal at 1173 K. It was found that Ni(II)- or In(III)-substitution for Fe(II) or Fe(III) in magnetite strongly enhances the phase transition from FeO to metallic phase to improve the efficiency for coal conversion. The reactive Ni(II)- and In(III)-ferrites were almost reduced to the metallic phases of Ni-Fe alloy and the mixture of alpha-Fe and In, respectively. The Ni(II)- and In(III)-ferrite reactions yielded high coal conversion of 60-70% which was about 3 times as large as that by a conventional single-step CO2 gasification of coal. In the second step, the reduced reactive ferrites were reoxidized with CO2 to generate CO at 1073 K. The metallic phase of alpha-Fe and In was completely converted to oxidized phases with CO2 while the Ni-Fe alloy could not be completely oxidized. The two-step process using In(III)-ferrite could be repeated with high coal conversions of 60-90% by resupplying the consumed coal to the system, although the conversion gradually decreased by the accumulation of ashes. Our findings suggest that the highly efficient net reaction CHn(coal) + CO2 --&gt; 2CO + n/2H(2) may be conducted using concentrated solar radiation as the energy source for high-temperature process heat below 1173 K.

    DOI: 10.1021/ef970236x

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  • Synthesis of Sn-incorporated folded sheets mesoporous materials (Sn-FSM-16)

    Y Kitayama, H Asano, T Kodama, J Abe, Y Tsuchiya

    JOURNAL OF POROUS MATERIALS   5 ( 2 )   139 - 146   1998年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:KLUWER ACADEMIC PUBL  

    Sn-incorporated folded sheets mesoporous materials (Sn-FSM-16) with various contents of Sn were synthesized by using a mixture of water glass, SnCl4 and NaOH as starting materials. Hexadecyltrimethyl-ammonium chloride (surfactant) was used to intercalate into the layered silicate. The reaction process was followed by measurements of XRD patterns of intermediates. The Sn-FSM-16 was formed via the following mechanism: (1) layered silicates such as alpha-, beta- and delta-Na2Si2O5 were formed as intermediates by the calcination of the mixture of the starting materials; (2) the surfactant was intercalated into the layered silicates; (3) the surfactant-silicate complex with hexagonal structure was obtained as a precursor of Sn-FSM-16; (4) the precursor was calcined to decompose the surfactant in the interlayer and was changed to Sn-FSM-16. The structural aspect of Sn in Sn-FSM-16 was studied by XPS profiles of Sn 3d(5/2) and Si-2p, Si-29 MAS NMR and FTIR. The content of Sn in Sn-FSM increased with increasing concentrations of both Sn and NaOH in the starting materials. The surface area of Sn-FSM-16 decreased with an increase of Sn content in Sn-FSM (1160-620 m(2)/g).

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  • Synthesis of titania pillared saponite in aqueous solution of acetic acid

    Y Kitayama, T Kodama, M Abe, H Shimotsuma, Y Matsuda

    JOURNAL OF POROUS MATERIALS   5 ( 2 )   121 - 126   1998年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:KLUWER ACADEMIC PUBL  

    The preparation of TiO2-pillared saponite was carried out in a CH3COOH aqueous solution. Titanium ion species to intercalate into the interlayer of saponite were obtained by an addition of Ti(C3H7O)(4) to an aqueous solution of CH3COOH and by subsequent aging of the solution for a prescribed time. Ti4+-intercalated saponite including organic materials was obtained by ion exchange. After the sample was calcined at 500 degrees C in air, TiO2-pillared saponite was obtained. The resulting TiO2-pillared saponite (Ti-Sapo) possessed surface areas in the range 300-400 m(2)/g and a sharp pore size distribution with the pore radius of 1.2 nm, The basal spacing of the product heated at temperature &gt;250 degrees C was about 2.45 nm. The pillar height of TiO2 in the Ti-Sapo was estimated to be 1.5 nm.

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  • Gas-liquid chromatographic analysis of geometrical and positional octadecenoic and octadecadienoic acid isomers produced by catalytic hydrogenation of linoleic acid on Ir/Al2O3

    Y Kitayama, M Takahashi, H Sugiyama, T Kodama, M Okamura

    JOURNAL OF THE AMERICAN OIL CHEMISTS SOCIETY   75 ( 1 )   27 - 32   1998年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER OIL CHEMISTS SOC  

    Catalytic hydrogenation of linoleic acid was studied on Ir/Al2O3. A detailed analysis of geometrical and positional isomers of octadecenoic acid (18:1) in the products was performed by capillary gas-liquid chromatography with a new capillary column coated with isocyanopropyl trisilphenylene siloxane (TC-70). Well-resolved peaks of 10 species of 18:1 were observed in the product. In addition to monoenoic acid isomers, four species of trans-dienoic isomers and conjugated dienoic isomers were found. From the distribution of 18:1 isomers, it was found that the double bond closer to the methyl end (Delta 12) showed higher reactivity than that closer to the carboxyl end (Delta 9) for hydrogenation. Because cis-8 18:1 and trans-8 18:1 were not observed but cis-10 18:1 and trans-10 18:1 were observed in the products, the double-bond Delta 9 did not migrate to the carboxyl end but migrated to the methyl end. On the other hand, the Delta 12 bond migrated to both methyl and carboxyl ends. From the distribution of 18:1 isomers in the reaction pathway, the hydrogenation of linoleic acid proceeds via half-hydrogenation states. Cis-18:1 isomers were produced predominantly in the initial stage of the reaction, while trans-18:1 isomers were produced during progress of the reaction. The cis/trans and positional isomerization took place by readsorption of 18:1 produced by the partial hydrogenation of linoleic acid.

    DOI: 10.1007/s11746-998-0005-z

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  • Efficient thermochemical cycle for CO2 reduction with coal using a reactive redox system of ferrite

    T Kodama, A Aoki, S Miura, Y Kitayama

    ADVANCES IN CHEMICAL CONVERSIONS FOR MITIGATING CARBON DIOXIDE   114   383 - 386   1998年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE PUBL B V  

    A two-step thermochemical process using a redox system of metal oxides for converting CO2 and coal to CO was studied on a number of iron-based oxides (ferrite) for the purpose of utilizing solar high-temperature heat. Reactions are done in a two-step redox cycle in which ferrite is reacted with coal powder at high temperatures to produce COx, H-2 (the 1st-step reaction) and metals which are reoxidized with CO2 to generate eO at lower temperatures in a separate step (the second-step reaction). In the 1st-step reaction, pure magnetite (Fe3O4) was readily reduced to FeO but the reduction from FeO to alpha-Fe scarcely proceeded by a short time reaction (30 min) with coal below 900 degrees C. It was found that Ni(II)- or In(III)-substitution for Fe(II) or Fe(III) in magnetite strongly enhances the phase transition from FeO to metallic phase to improve the efficiency for coal conversion. The efficiency of the reaction by the two-step cycle using a reactive ferrite is superior to that by a conventional single-step CO2 gasification of coal. Our findings suggest that highly endothermic CO2 reduction with coal will be conducted using concentrated solar radiation as the energy source for high-temperature process below 900 degrees C.

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  • Efficient Two-Step Thermochemical Process Using Highly Reactive Metal Oxide for Conversion of High-Temperature Heat to Chemical Fuels

    Recent Res. Devel. in Mat. Sci.   1   109 - 121   1998年

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  • Oxidative Coupling of Methane using H<sub>2</sub>O as An Oxidant over Ferrite Catalysts

    SHIMIZU T., KITAYAMA Y., KODAMA T.

    日本応用磁気学会誌   22 ( S1 )   400 - 402   1998年

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    記述言語:英語   出版者・発行元:公益社団法人 日本磁気学会  

    &nbsp;&nbsp;The following reaction has been investigated over various metal oxides for the purpose of utilizing solar or nuclear heat as an energy source: (4+x) CH<sub>4</sub> + xH<sub>2</sub>O &rarr; 2C<sub>2</sub>H<sub>4</sub> + xCO + (3x+4)H<sub>2</sub>. Oxides of Zn, Mn, Co, Ni, Mg, and Fe were used at 900 &deg;C. The greatest activity for C<sub>2</sub>H<sub>4</sub> formation was observed with Fe<sub>3</sub>O<sub>4</sub> (magnetite). Substitution of Mn(II) for Fe(II) in magnetite slightly increased the activity for C<sub>2</sub>H<sub>4</sub> formation. The surface-lattice oxygens of the wustite (FeO) phase formed by the reduction of MFe<sub>2</sub>O<sub>4</sub> (M = Fe, Zn, Mn) with CH<sub>4</sub> are believed to be active in the oxidation of CH<sub>4</sub> to C<sub>2</sub>H<sub>4</sub>. If this oxidative coupling over MnFe<sub>2</sub>O<sub>4</sub> is combined with the reverse water gas shift reaction, the highly endothermic reaction 13CH<sub>4</sub> + 9H<sub>2</sub>O &rarr; 2C<sub>2</sub>H<sub>4</sub> + 9CO + 31H<sub>2</sub> is realized below 900&deg;C.

    DOI: 10.3379/jmsjmag.22.S1_400

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  • New Ferrite Application for a Thermochemical CO<sub>2</sub> Reduction with Coal

    MIURA S., AOKI A., KITAYAMA Y., KODAMA T.

    日本応用磁気学会誌   22 ( S1 )   403 - 405   1998年

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    記述言語:英語   出版者・発行元:公益社団法人 日本磁気学会  

    &nbsp;&nbsp;This paper proposes a new application of ferrites for a thermochemical reduction of CO<sub>2</sub> to CO with coal. Reactions are done in a two-step redox cycle:<br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;1) ferrite + CH<sub>&tau;</sub> &rarr; reduced ferrite + xCO + (1-x)CO<sub>2</sub> + &tau;/2H<sub>2</sub><br>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;2) reduced ferrite + (2-x)CO<sub>2</sub> &rarr; ferrite + (2-x)CO,<br>where CH<sub>&tau;</sub> represents coal. A number of the systems of ferrites mixed with active carbon have been screened to find the most reactive ferrite for the first-step reaction. The Ni(II)-ferrite showed the greatest reactivity. Efficient net reaction CH<sub>&tau;</sub> + CO<sub>2</sub> &rarr; 2CO + &tau;/2H<sub>2</sub> was demonstrated by the proposed two-step process using the mixture of Ni(II)-ferrite and australian bituminous coal in the temperature range of 800-900&deg;C. Our findings suggest that highly endothermic CO<sub>2</sub> reduction with coal will be conducted using concentrated solar radiation as the energy source below 900&deg;C.

    DOI: 10.3379/jmsjmag.22.S1_403

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  • New Synthesis Method of Ultrafine Ferrite by Reduction of Fe(III)-Tartrate Chelate Solution

    KODAMA T., MIURA S., KITAYAMA Y., TAMAURA Y.

    日本応用磁気学会誌   22 ( S1 )   440 - 442   1998年

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    記述言語:英語   出版者・発行元:公益社団法人 日本磁気学会  

    &nbsp;&nbsp;Ultrafine ferrites, represented by x(MFe<sub>2</sub>O<sub>4</sub>)-y(Fe<sub>3</sub>O<sub>4</sub>)-z(Fe<sub>2</sub>O<sub>3</sub>), where x+y+z=1, were synthesized by the reduction (with dextrose) of the strongly alkaline Fe(III)-tartrate solutions containing M(II) ions (M(II) = Zn(II), Ni(II) and Cd(II)) at 100&deg;C. The particles with the average crystallite size ranging from 20 to 50 nm were obtained. The strongly alkaline solution of Fe(III)-tartrate yielded red-brown precipitates giving very broad peaks of the spinel type compound in the XRD pattern without any reduction processes at 100&deg;C. The Fe(II) ions formed by the reduction of the Fe(III) ions favor the formation of the ferrite particles. The M&ouml;ssbauer data showed that the vacancies, Fe(II) and Ni(II) ions were distributed in the octahedral sites, and Zn(II) and Cd(II) ions in the tetrahedral sites.

    DOI: 10.3379/jmsjmag.22.S1_440

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  • Stabilization of superionic conduction phase in Li3Sc2(PO4)(3) 査読

    T Suzuki, K Yoshida, K Uematsu, T Kodama, K Toda, ZG Ye, M Sato

    SOLID STATE IONICS   104 ( 1-2 )   27 - 33   1997年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Lithium superion conductors, Li3+2x(Sc1-xMgx)(2)(PO4)(3), Li3-2x(Sc1-xMx)(2)(PO4)(3) (M=Ti, Zr, Sn, Hf) and Li3-4x(Sc1-xMx)(2)(PO4)(3) (M = Nb, Ta) were prepared by a solid-state reaction. TG-DTA analysis indicated no phase transition in Li3+2x(Sc1-xMgx)(2)(PO4)(3) and Li3-2x(Sc1-xMx)(2)(PO4)(2) (M = Ti, Zr, Sn, Kf) with x higher than 0.05, and in Li3-4x(Sc1-xMx)(2)(PO4)(3) (M=Nb, Ta) with x higher than 0.025. The room temperature ionic conductivity of Li3Sc2(PO4)(3) has been increased by three orders of magnitude with the highest conductivity observed in Li3-2x(Sc1-xTix)(2)(PO4)(3) with x = 0.20 and in Li3-2x(Sc1-xZrx)(2)(PO4)(3) with x = 0.10. It was ascribed to the stabilization of the high temperature superionic conduction phase and the introduction of vacancies on the Li+ sites by substituting Ti4+ Or Zr4+ for Sc3+.

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  • Thermochemical conversion of coal and water to CO and H-2 by a two-step redox cycle of ferrite

    T Kodama, S Miura, T Shimizu, Y Kitayama

    ENERGY   22 ( 11 )   1019 - 1027   1997年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Redox systems of iron-based oxides (ferrites) mixed with coal powder have been studied to determine the most reactive and selective working materials for thermochemical conversion of coal and water to CO and H-2. Reactions were performed in a two-step redox cycle in which the ferrites were reacted with coal powder at 900 degrees C to produce CO, H-2, and reduced ferrites (coal-gasification step); these were then reoxidized with water vapor to generate H-2 at 700 degrees C in a separate step (water-decomposition step). Magnetite and Mg(II)-, Mn(II)-, Ni(II)-, Zn(II)-, and In(III)-ferrites have been screened for reactivity and selectivity in the coal-gasification step. The In(III)-ferrite showed the greatest reactivity and selectivity for CO formation from coal at 900 degrees C. The CO-production rate in the coal-In(III)-ferrite reaction was 3.5 times as fast as that in the single-step direct coal-H2O reaction. The metallic phase of alpha-Fe and In, produced by the coal-In(III)-ferrite reaction, was reoxidized to the ferrite phase to generate I-I, in the water-decomposition step at 700 degrees C. The amount of H-2 evolved using In(III)-ferrite was 5 times larger than that using magnetite. The processes were repeated in the temperature range 700-900 degrees C, with the highly efficient net reaction CHtau(coal) + H2O --&gt; CO + (tau/2 + 1)H-2. (C) 1997 Elsevier Science Ltd.

    DOI: 10.1016/S0360-5442(97)00041-8

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  • High-temperature conversion of CH4 to C-2-hydrocarbons and H-2 using a redox system of metal oxide

    T Kodama, T Shimizu, A Aoki, Y Kitayama

    ENERGY & FUELS   11 ( 6 )   1257 - 1263   1997年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CHEMICAL SOC  

    A high-temperature thermochemical process using a redox system of metal oxide is proposed for converting CH4 to C-2-hydrocarbons (C-2-HCs) and H-2. Reactions were performed in a two-step redox cycle. In the first high-temperature and endothermic step, methane is reacted with metal oxide to produce C-2-HCs and the reduced metal oxide. The reduced metal oxideis reoxidized with water to generate H-2 at a low temperature in the second step. A thermodynamic analysis showed that redox systems of Fe3O4/FeO, SnO2/SnO, and WO3/WO2 are promising for the two: step process. The redox system of Fe3O4 was experimentally examined. Highly selective conversion could be repeated with SiO2-supported Fe3O4 (Fe3O4/SiO2) to produce C-2-HCs (mainly C2H4) and H-2 alternately in the different steps at temperatures from 1123 to 1173 K; evolution of COx and deposition of bulk carbon were scarcely observed. Experimental studies using unsupported Fe3O4 showed that the formation of C-2-HCs in the first high-temperature step occurred favorably for the reduction from Fe3O4 to FeO in comparison to that from FeO to alpha-FeO. The two-step process using Fe3O4/SiO2 is superior to the production efficiencies of C-2-HCs and H-2 obtained by the direct single-step conversion of CH4; which offers the efficient conversion of natural gas utilizing high-temperature heat such as concentrated solar radiation.

    DOI: 10.1021/ef9700691

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  • Catalytic reduction of carbon dioxide on Ni-Cu alloys 査読

    Y Kitayama, Y Watanabe, K Muramatsu, T Kodama

    ENERGY   22 ( 2-3 )   177 - 182   1997年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Catalytic reduction of CO2 with H-2 was studied on Ni/SiO2, Ni1-xCux/SiO2 (x=0.05-0.9) and Cu/SiO2 in a closed circulating reaction system in order to obtain a highly active and selective catalyst for CO formation. The yield of CO from CO2+H-2 on Cu/SiO2 was about 60% and its selectivity was 97% or more. In a Cu-rich region, Ni-Cu catalysts exhibited high selectivity for CO formation, while CH4 was produced predominantly in a Ni-rich region. The activity of Ni0.1Cu0.9/SiO2 for the selective reduction of CO2 to CO was enhanced by twice that of Cu alone by the addition of small amounts of Ni. Copyright (C) 1996 Elsevier Science Ltd.

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  • Methanation of CO2 using ultrafine NixFe3-xO4

    T Kodama, Y Kitayama, M Tsuji, Y Tamaura

    ENERGY   22 ( 2-3 )   183 - 187   1997年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Ultrafine Ni(II)-ferrites (NixFe3-xO4, x=0.14-1.0; UNFs) with a high reactivity for CO2 methanation have been synthesized by the hydrolysis of Ni2+, Fe2+ and Fe3+ ions at 60-90 degrees C, followed by heating of the co-precipitates to 300 degrees C. The crystallite sizes of the UNFs ranged from 14 to 17 nm. The ferrite particles, size-controlled in the nanoscale range, improved the methanation reactivity. In an H-2/CO2 mixed gas-flow system at 300 degrees C, the CH4 yield with UNF was 1.6 times as large as that using Ni(II)-ferrite with a crystallite size of 100-200 nm prepared by the conventional wet method. The maximum yield (40%) and selectivity (95%) for CH4 were obtained at the Ni2+-substitution of x=0.36 in UNF. The XRD analysis showed that only the oxygen-deficient Ni(II)-ferrite phase was formed in the UNF with x=0.36 during methanation. For x &gt;0.36, the carbide phase was formed in the UNF during methanation. The formation of the carbide phase-deactivated the ultrafine oxygen-deficient Ni(II)-ferrite. Copyright (C) 1996 Elsevier Science Ltd.

    DOI: 10.1016/S0360-5442(96)00097-7

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  • Preparation and CO2 methanation activity of an ultrafine Ni(II) ferrite catalyst

    M Tsuji, T Kodama, T Yoshida, Y Kitayama, Y Tamaura

    JOURNAL OF CATALYSIS   164 ( 2 )   315 - 321   1996年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS  

    Ultrafine Ni(II) ferrite (UNF) with 36% Ni2+ substitution for Fe2+ in magnetite has been synthesized in order to study its catalytic activity and selectivity toward CO2 methanation at 300 degrees C. Ni(II) ferrites were prepared by two different methods: (1) coprecipitation of Ni2+, Fe2+, and Fe3+ at 60 degrees C followed by heating to 300 degrees C and (2) oxidation of aqueous suspension of Fe2+ and Ni2+ hydroxides at 65 degrees C (oxidation method). The BET surface area of the initial UNF synthesized by coprecipitation was 73 m(2) g(-1), eight times as large as that of the Ni(II) ferrite obtained by the oxidation method (NF; 9 m(2) g(-1)). It rapidly decreased to 26 m(2) g(-1) by sintering in the initial stage of methanation. The yield of CH4 obtained on the UNF catalyst was 1.5-6.0 times larger than that on the NF catalyst in a 2-h run of the methanation, depending on a flow rate of reactant H-2/CO2 mixed gas. It was found that the selectivity for CH4 was much improved in UNF (96%) in comparison with NE XRD and chemical analysis showed that the UNF and NF were transformed to oxygen-deficient ferrite forms during the methanation. The specific activity (mol m(-2) s(-1)) of UNF for CH4 formation was rather lower than that of NF, about half the activity of NF, which could be explained assuming that oxygen sublattice points on the catalyst surface formed by H-2 reduction serve as active sites for methanation. On the other hand, the activity for CO formation significantly decreased on UNF, due to the change in the nature of the active site. (C) 1996 Academic Press, Inc.

    DOI: 10.1006/jcat.1996.0387

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  • Synthesis and characterization of ultrafine Mn(II)-bearing ferrite of type MnxFe3-xO4 by coprecipitation

    T Kodama, M Ookubo, S Miura, Y Kitayama

    MATERIALS RESEARCH BULLETIN   31 ( 12 )   1501 - 1512   1996年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Ultrafine Mn(II)-ferrites represented by MnxFe3-xO4 (x = 0.19-0.84) were synthesized by hydrolysis of Mn2+, Fe2+, and Fe3+ ions, followed by aging of the coprecipitate at 60 degrees C without any hydrothermal and heat treatments. Nearly spherical and uniform particles were formed, the average crystallite size of which ranged from 8 to 13 nm. The Mn2+ substitution of the ultrafine ferrite was corroborated by a linear increase in the lattice constant with an increase in the Mn(II) content of the products. The Mossbauer spectra revealed that the superparamagnetic fraction was small in the samples at room temperature, and the ultrafine particles were almost ferrimagnetic. In the absence of Fe2+, the coprecipitation of Mn2+ and Fe3+ (the Mn(II)/Fe-total mole ratio = 0.5) resulted in an amorphous compound, indicating that the Fe2+ ions facilitate the formation of the spinel ferrite during neutralization of the metal ions. This effect of Fe(II) ions on the ferrite formation can be attributed to the formation of dark red complex cation composed of Fe(II), Fe(III) and Mn(II) as the intermediate into ferrite. The magnetic properties of the ultrafine ferrites at room temperature were also given.

    DOI: 10.1016/S0025-5408(96)00146-8

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  • Catalytic acceleration for CO2 decomposition into carbon by Rh, Pt or Ce impregnation onto Ni(II)-bearing ferrite

    M Tsuji, T Yamamoto, Y Tamaura, T Kodama, Y Kitayama

    APPLIED CATALYSIS A-GENERAL   142 ( 1 )   31 - 45   1996年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ELSEVIER SCIENCE BV  

    Catalyzing effects of impregnated Rh, Pt and Ce on Ni(II)-bearing ferrite (NF) activated with H-2 have been studied for CO2 decomposition to carbon at 300 degrees C. The activation rate of the Rh- or Pt-impregnated NF with H-2 gas was about 1.6 times as large as that of the NF alone at 300 degrees C. At 250 degrees C, the Rh- and Pt-NFs were also activated at 1.6 and 1.3 times higher rates than that of NF control, respectively. The activation of NF was, however, not enhanced by the impregnation of Ce. The rates of CO2 decomposition using these activated materials were 1.2-3.0 times as large as that of the activated NF. The effect of metal impregnation on the activation and CO2 decomposition increased in the order of Ce &lt; Pt &lt; Rh. This catalyzing effect is attributed to hydrogen and oxygen spillovers through accelerated dissociations of H-2 and CO2 molecules, respectively, on the surface of Rh, Pt or Ce deposited on the NF.

    DOI: 10.1016/0926-860X(96)00050-6

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  • Preparation of large surface area nickel magnesium silicate and its catalytic activity for conversion of ethanol into buta-1,3-diene

    Y Kitayama, M Satoh, T Kodama

    CATALYSIS LETTERS   36 ( 1-2 )   95 - 97   1996年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:BALTZER SCI PUBL BV  

    The ternary oxide catalysts of nickel magnesium silicate with a large surface area (498-784 m(2)/g) can be obtained by calcining a mixture of Ni(NO3)(2), Mg(OH)(2) and SiO2. The large surface area of the catalyst is attributed to its layer structure. The selectivity for buta-1,3-diene formation from ethanol on the catalysts was 90% or more and the yield of buta-1,3-diene was 53 mol%.

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  • Characterization of Ultrafine Ni_xFe_<3-x>O_4 Particles Synthesized by Co-Precipitation: Size Regulation and Magnetic Properties

    KODAMA T., KITAYAMA Y., TSUJI M., TAMAURA Y.

    日本応用磁気学会誌   20 ( 2 )   305 - 308   1996年

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    記述言語:英語   出版者・発行元:The Magnetics Society of Japan  

    Ultrafine Ni(II)-bearing ferrites (UNFs) with 14-100% Ni(II)-substitution of <i>x</i> in Ni<sub><i>x</i></sub>Fe<sub>3-<i>x</i></sub>O<sub>4</sub> for Fe<sup>2+</sup> in magnetite were synthesized by hydrolysis of Ni<sup>2+</sup>, Fe<sup>2+</sup>, and Fe<sup>3+</sup> ions at 60°C,followed by aging of the co-precipitates at 60°C and eating to 300°C. The aged precipitates were the precursors of the UNFs, into which they were transformed by heating at 300°C The Ni(II)-substitution of the UNF was corroborated by a decrease in the lattice constant with an increase in the Ni(II) content of the product. The ferrite particles were nearly spherical and uniform. The average crystallite sizes ranged from 8 to 17 nm, which decreased with an increase in the Ni(II)ontent of the ferrite. In the average size range from 14 to 17 nm, the UNFs with various Ni (II)substitutions could be synthesized by changing the aging conditions. A transtion of the UNF (<i>x</i>= 1.0) from superparamagnetic to ferrimagnetic particles at room temperature occurred in the crystallite size range from 8 to 14 nm. The UNFs gave a room temperature saturation magnetization (<i>M</i><sub>s</sub>)much lower than the theoretical <i>M</i><sub>s</sub>.

    DOI: 10.3379/jmsjmag.20.305

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  • XRD AND MOSSBAUER STUDIES ON OXYGEN-DEFICIENT NI(II)-BEARING FERRITE WITH A HIGH REACTIVITY FOR CO2 DECOMPOSITION TO CARBON

    T KODAMA, M TABATA, T SANO, M TSUJI, Y TAMAURA

    JOURNAL OF SOLID STATE CHEMISTRY   120 ( 1 )   64 - 69   1995年11月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ACADEMIC PRESS INC JNL-COMP SUBSCRIPTIONS  

    CO2 decomposition to carbon at 300 degrees C was studied using H-2-reduced Ni(II)-bearing ferrite. The oxygen-deficient Ni(II)bearing ferrite (ODNF: Ni0.39Fe2.61O4-delta) was formed by H-2-reduction of Ni0.39Fe2.61O4 (NF) at 300 degrees C. The ODNF was characterized by X-ray diffractometry and Mossbauer spectroscopy before and after CO2 decomposition, The oxygen deficiency (delta) of ODNF increased with an increase in an H-2-reduction time, It decreased after CO2 decomposition, The reactivity of ODNF for CO2 decomposition increased with a higher delta value. The lattice constant of the ODNF was larger than that of the stoichiometric NF, which decreased, approaching the stoichiometric value after CO2 decomposition, Mossbauer spectra suggest that excess iron ions in interstices of octahedral sites migrate to tetrahedral sites in a spinel structure of the ferrite by incorporating oxygens from CO2 during CO2 decomposition. (C) 1995 Academic Press, Inc.

    DOI: 10.1006/jssc.1995.1377

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  • SYNTHESIS AND CHARACTERIZATION OF ULTRAFINE NICKEL(II)-BEARING FERRITES (NIXFE3-XO4,X=0.14-1.0)

    T KODAMA, Y WADA, T YAMAMOTO, M TSUJI, Y TAMAURA

    JOURNAL OF MATERIALS CHEMISTRY   5 ( 9 )   1413 - 1418   1995年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    Ultrafine Ni-II-bearing ferrites (UNFs) with 14-100% Ni2+-substitution (x in NixFe3-xO4) for Fe2+ in magnetite have been synthesized by hydrolysis of Ni2+, Fe2+ and Fe3+ ions at 60 degrees C, followed by aging of the co-precipitates at 60 degrees C and heating to 300 degrees C. The aged co-precipitates (ACPs) obtained at an Ni-II/Fe-total mole ratio r=0.05-0.30 (x=0.14-0.69) in the starting solution gave the relatively sharp peaks of the spinel structure in the XRD patterns. At r&gt;0.40 (x greater than or equal to 0.85), the spinel peaks were broader as r increased. The IR spectra of the ACPs showed that, with increasing the r value to r greater than or equal to 0.30, the ACP approached an amorphous phase in which OH- groups and/or coordinated water remained, indicating that the Fe-II ions enhance the dehydration of the ACP. The ACPs were the precursors of the UNFs, and were transformed into the UNFs by heating to 300 degrees C. The Ni2+-substitution of the UNFs was corroborated by a linear decrease in the lattice constant with an increase in the Ni2+ content of the product. The average crystallite sizes ranged from 8 to 17 nm. The transition from a magnetically split pattern to a doublet in the room-temperature Mossbauer spectra of the UNFs corresponded to a decrease in the average crystallite size, indicating superparamagnetic behaviour of ultrafine ferromagnetic particles. The UNFs gave a room-temperature saturation magnetization (M(s)) much lower than the theoretical M(s) values.

    DOI: 10.1039/jm9950501413

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  • CO2 DECOMPOSITION TO CARBON BY ULTRAFINE NI(II)-BEARING FERRITE AT 300-DEGREES-C

    T KODAMA, Y WADA, T YAMAMOTO, M TSUJI, Y TAMAURA

    MATERIALS RESEARCH BULLETIN   30 ( 8 )   1039 - 1048   1995年8月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Ultrafine Ni(II)-bearing ferrite (UNF) Ni0.362+Fe0.452+Fe2.193+O4.10 was synthesized with a view to investigating materials with the high reactivity toward CO2--&gt; C decomposition. UNF was prepared by coprecipitation of Ni2+ Fe2+ and Fe3+ with NaOH. The electron micrographs of the UNFs showed their size to be 16-29 nm in diameter. The rate of the H-2-reduction of UNF was 3 times faster than that of conventional Ni(II)-bearing ferrite (NF) with the size of 100-200 nm prepared by the wet method. The H-2-reduced UNF with the spinel structure revealed the much improved reactivity toward CO2 decomposition. The initial rate and amount of CO2 decomposition for the UNFs were 6.5 and 2.5 times greater than those for NF with the same Ni content at 300 degrees C. Such high reactivity of UNF is attributed to both the level of activation and surface area in comparison with NF

    DOI: 10.1016/0025-5408(95)00077-1

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  • SYNTHESIS OF HYDROTALCITE WITH HIGH LAYER CHARGE FOR CO2 ADSORBENT

    T YAMAMOTO, T KODAMA, N HASEGAWA, M TSUJI, Y TAMAURA

    ENERGY CONVERSION AND MANAGEMENT   36 ( 6-9 )   637 - 640   1995年6月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    Hydrotalcite-like compounds (HT) with 24% to 48% Al3+-substitution have been synthesized in the Mg2+-Al3+-Fe(CN)(6)(4-) system. Conditioning of the synthesized and air-dried compound with K4Fe(CN)(6)(4-) solution at 80 degrees C was essential to obtain the 80-90% pure ionic Fe(CN)(6)(4-) form on an equivalent basis. A linear decrease in a(o) with an increase in the mole ratio of R=Al3+/(Mg2+Al3+) was extended to R=0.48. The CO2 adsorption profiles were dependent upon both the interlayer distance and the Al3+-substitution. The expanded space with the large anion Fe(CN)(6)(4-) can accommodate more effectively CO2 gas in comparison with the NO3- and mixed ionic forms. The optimum space and charge density in the interlayer as a CO2 adsorption field could be found on the hydrotalcite with the Al3+-substitution of 37 %. The isosteric heat of CO2 adsorption was 43.3 kJ mol-1 in the range of adsorption of 20 to 40 cm(3) g(-1) at 298 K and 0.1 MPa.

    DOI: 10.1016/0196-8904(95)00086-S

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  • REACTION CONDITION FOR THE SYNTHESIS OF ULTRAFINE PARTICLES OF THE HIGH-VACANCY-CONTENT ZN(II)-BEARING FERRITES FROM IRON(III) TARTRATE SOLUTION

    T KODAMA, Y TAMAURA

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY   78 ( 5 )   1335 - 1342   1995年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:WILEY-BLACKWELL  

    Reaction conditions for the synthesis of ultrafine particles of ferrite solid solutions between ZnFe2O4 and gamma-F2O3 represented by x(ZnFe2O4)-y(Fe3O4)-z(gamma-Fe2O3), where x + y + z = 1(0.09 less than or equal to x less than or equal to 0.73, y less than or equal to 0.08, 0.22 less than or equal to z less than or equal to 0.88) (high-vacancy-content Zn(II)-bearing ferrites), were studied using the strongly alkaline solutions of Fe(III) tartrate containing Zn(II) ions at 100 degrees C, The crystal growth of the ferrite particles was enhanced with the Zn(II) ions in the reaction solution, The number of nuclei of the ferrite was dependent on the Fe(III) or the tartrate concentration, which influenced the ultrafine particle size of the ferrite. The average particle size of the high-vacancy-content Zn(II)-bearing ferrites ranged from 7 to 38 nm, The room-temperature Mossbauer effect of the high-vacancy content Zn(II)-bearing ferrite (x = 0.34-0.37, y less than or equal to 0.02, z = 0.62-0.65) revealed the superparamagnetic nature for ultrafine particle sizes less than 20 nm, The ferrite was transferred from superparamagnetic to ferrimagnetic with an increase in the particle size (&gt;20 nm) at room temperature.

    DOI: 10.1111/j.1151-2916.1995.tb08491.x

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  • CO2 DECOMPOSITION TO CARBON WITH FERRITE-DERIVED METALLIC PHASE AT 300-DEGREES-C

    T KODAMA, T SANO, T YOSHIDA, M TSUJI, Y TAMAURA

    CARBON   33 ( 10 )   1443 - 1447   1995年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:PERGAMON-ELSEVIER SCIENCE LTD  

    CO2 decomposition to carbon was studied on alpha-Fe and Fe-Ni alloy formed by H-2-reduction of magnetite and Ni(II)-bearing ferrite at 300 degrees C. The metallic phases were transformed to ferrite phase by incorporating oxygen from CO2. The integrated amount of decomposed CO2 reached 30 mmol CO2 g(-1) of Fe3O4 by repeating the H-2 reduction and CO2 decomposition 9 times. The decomposition of CO2 on the H-2-reduced magnetite was kept nearly constant at 72-86%, irrespective of the run number. A small portion of the alpha-Fe was transformed to carbide in the Ist run; however, the formation of carbide scarcely proceeded by repeating these processes on magnetite. The decomposition reactivity of H-2-reduced Ni(II)-bearing ferrite decreased gradually. The integrated amount of decomposed CO2 was 20 mmol CO2 g(-1) of Ni0.39Fe2.61O4 by repeating the processes 11 times. For Ni(II)-bearing ferrite, the formation of carbide proceeded more effectively. The lower reactivity of H-2-reduced Ni(II)-bearing ferrite for CO, decomposition will be due to the formation of carbide.

    DOI: 10.1016/0008-6223(95)00094-T

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  • METHANATION OF CO2 ON H-2-REDUCED NI(II) OR CO(II)-BEARING FERRITES AT 200-DEGREES-C

    M TSUJI, H KATO, T KODAMA, SG CHANG, N HESEGAWA, Y TAMAURA

    JOURNAL OF MATERIALS SCIENCE   29 ( 23 )   6227 - 6230   1994年12月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CHAPMAN HALL LTD  

    The methanation of CO2 gas at 200 degrees C was investigated in Co(II) or Ni(II)-bearing ferrites with substitution of up to 0.262 and 0.143, respectively. The metal substitution in the ferrite facilitated the methanation of the deposited carbon from CO2 gas in the H-2-reduced M(II)-bearing ferrite in comparison with the reactivity of the H-2-reduced magnetite with the same spinel structure. The effect on the reactivity of methanation was found to be much larger in Ni(II)-substitution. The degree of the effect increased with increases in the Ni(II)-substitution, while it remained about the same with increases in the Co(II) -substitution. The maximum methanation (86.9%) of CO2 was attained in the Ni(II)-bearing ferrite activated by H-2 gas for 3.0 h.

    DOI: 10.1007/BF00354564

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  • DECOMPOSITION OF CO2 TO CARBON BY H-2-REDUCED NI(II)- AND CO(II)-BEARING FERRITES AT 300-DEGREES-C

    T KODAMA, H KATO, SG CHANG, N HASEGAWA, M TSUJI, Y TAMAURA

    JOURNAL OF MATERIALS RESEARCH   9 ( 2 )   462 - 467   1994年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:MATERIALS RESEARCH SOCIETY  

    Ni(II)- and Co(II)-bearing ferrites with different levels of metal substitution have been studied for CO2 decomposition. Ni2+ and Co2+ have been substituted for Fe2+ or Fe3+ in magnetite with the spinel type of crystal structure up to 14% and 26% for the mole ratio of Ni2+ and Co2+ to the total Fe contents, respectively. The metal substitution was corroborated by Mossbauer spectroscopy and XRD studies. They were activated in a flow of HZ gas to form oxygen-deficient ferrites with the spinel structure retained. The oxygen-deficient M(II)-bearing ferrites have been found to show high reactivity toward CO2 decomposition to carbon at 300 degrees C. The reactivity increased with the level of metal substitution and activation. The oxygens of CO2 were incorporated into the spinel structure and carbon was deposited on the surface of the ferrites. The deposited carbon was visible on dissolution of the ferrites used. The rate of decomposition on H-2-activated Ni(II)-bearing ferrite with the mole ratio of 14% was 30 times as high as that of H-2-activated magnetite.

    DOI: 10.1557/JMR.1994.0462

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  • CO2 DECOMPOSITION WITH MANGANO-WUSTITE

    M TABATA, H KATO, T KODAMA, T YOSHIDA, M TSUJI, Y TAMAURA

    JOURNAL OF MATERIALS SCIENCE   29 ( 4 )   999 - 1003   1994年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CHAPMAN HALL LTD  

    Mn(II)-ferrite (Mn0.97Fe2.0204.00) prepared by the wet method was reduced in a hydrogen at 300 C to form highly reactive mangano-wustite ((Fe0.67, Mn0.32) 0) for CO2 decomposition. Approximately 23% CO2 injected (3.40 mmol) was decomposed to CO by the mangano-wustite (3.22 g) in the initial stage of the reaction in a batch system at 400-degrees-C. 88% CO was further decomposed to carbon. Approximately 58% CO2 injected was reversibly adsorbed on the surface and the remaining 12% was unchanged after 200 h reaction. The mangano-wustite was concurrently transformed to Mn(II)-bearing ferrite (Mn0.23Fe2.7704.00) and manganese-rich mangano-wustite ((Fe0.60, Mn0.40)O). The higher CO2 decomposition capacity for this mangano-wustite than that for oxygen-deficient Mn(II)-ferrite is discussed in detail, based on electron hopping and movement of ions in the bulk.

    DOI: 10.1007/BF00351423

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  • Decomposition of carbon dioxide to carbon by hydrogen-reduced Ni(II)-bearing ferrite

    H. Kato, T. Kodama, M. Tsuji, Y. Tamaura, S. G. Chang

    Journal of Materials Science   29 ( 21 )   5689 - 5692   1994年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:Kluwer Academic Publishers  

    Hydrogen-activated Ni(II)-bearing ferrite, Ni0.37 2+Fe0.49 2+Fe2.09 3+O4.00, showed a high rate of decomposition of carbon dioxide to carbon at 300°C. This is based on the redox process of the Ni(II)-bearing ferrite with the spinel type of crystal structure. The rates of both activation by hydrogen gas and oxidation in carbon dioxide gas were much improved in the Ni (II)-bearing ferrite. The rate of decomposition was 0.178 mol h-1 for the activated Ni(II)-bearing ferrite and 0.005 92 mol h-1 for the activated magnetite in the batch mode, being 30 times larger. The rate of carbon dioxide decomposition was 16 times higher in the flow system in comparison with that of the activated magnetite. © 1994 Chapman &amp
    Hall.

    DOI: 10.1007/BF00349965

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  • METHANATION OF CO2 WITH H2-REDUCED MAGNETITE

    T YOSHIDA, K NISHIZAWA, M TABATA, H ABE, T KODAMA, M TSUJI, Y TAMAURA

    JOURNAL OF MATERIALS SCIENCE   28 ( 5 )   1220 - 1226   1993年3月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CHAPMAN HALL LTD  

    The methanation reaction of CO2 was studied with H-2-reduced magnetite. A high conversion ratio of about 0.9 (in 30 min of the reaction time) with a selectivity of nearly 100% was obtained at 300-degrees-C and at 0.1 MPa for H2-reduced magnetite which had been prepared by passing H-2 gas for 1-5 h at 300-degrees-C. From the results of X-ray diffractometry and Mossbauer spectroscopy, and from chemical analysis of the deposited carbon, H-2-reduced magnetite is considered to decompose adsorbed CO2 into carbon, and to incorporate the oxygen of the CO2 into the spinel-type structure of the magnetite, associated with oxidation of the Fe2+ ion into Fe3+ ion in the magnetite. The high conversion ratio in the methanation reaction is considered to come from a higher reactivity of the elementary carbon deposited on the surface of the H-2-reduced magnetite.

    DOI: 10.1007/BF01191956

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  • CO2 DECOMPOSITION WITH OXYGEN-DEFICIENT MN(II) FERRITE

    M TABATA, Y NISHIDA, T KODAMA, K MIMORI, T YOSHIDA, Y TAMAURA

    JOURNAL OF MATERIALS SCIENCE   28 ( 4 )   971 - 974   1993年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CHAPMAN HALL LTD  

    An oxygen-deficient Mn(II) ferrite (Mn0.97Fe2.02O3.92) was synthesized and its reactivity to reduce CO2 gas into carbon was studied at 300-degrees-C. The oxygen-deficient Mn(II) ferrite was obtained by flowing H-2 gas through Mn(II) ferrite with a nearly stoichiometric composition of Mn0.97Fe2.02O4.00 at 300-degrees-C. The lattice constant of the oxygen-deficient Mn(II) ferrite (0.8505 nm) is larger than that of the Mn(II) ferrite with a nearly stoichiometric composition (0.8498 nm). The chemical composition of the Mn(II) ferrite changed from Mn0.97Fe2.02O4.00 to Mn0.97Fe2.02O3.92 during the H-2 reduction process, indicating that the oxygen is deficient in the spinel structure of the Mn(II) ferrite. This was confirmed by Mossbauer spectroscopy and X-ray diffractometry. The efficiency of CO2 decomposition into carbon at 300-degrees-C with the oxygen-deficient Mn(II) ferrite was much lower by about 10(5) than that of oxygen-deficient magnetite. This is considered to be due to the difference in electron conductivity between Mn(II) ferrite and magnetite, which determines the reductivity for CO2 into carbon by donation of an electron at the adsorption site.

    DOI: 10.1007/BF00400881

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  • CARBON-DIOXIDE DECOMPOSITION INTO CARBON WITH THE RHODIUM-BEARING MAGNETITE ACTIVATED BY H-2-REDUCTION

    K AKANUMA, K NISHIZAWA, T KODAMA, M TABATA, K MIMORI, T YOSHIDA, M TSUJI, Y TAMAURA

    JOURNAL OF MATERIALS SCIENCE   28 ( 4 )   860 - 864   1993年2月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CHAPMAN HALL LTD  

    The CO2 decomposition into carbon with the rhodium-bearing activated magnetite (Rh-AM) was studied in comparison with the activated magnetite (AM). The Rh-AM and the AM were prepared by flowing hydrogen gas through the rhodium-bearing magnetite (Rh-M) and the magnetite (M), respectively. The rate of activation of the Rh-M to the Rh-AM was about three times higher than that of the M to the AM at 300-degrees-C. The reactivity for the CO2 decomposition into carbon with the Rh-AM (70% CO2 was decomposed in 40 min) was higher than that with the AM (30% in 40 min) at 300-degrees-C. The Rh-M was activated to the Rh-AM at a lower temperature of 250-degrees-C, and the Rh-AM decomposed CO2 into carbon at 250-degrees-C. On the other hand, the M was little activated at 250-degrees-C.

    DOI: 10.1007/BF00400865

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  • DECOMPOSITION OF CO2 AND CO INTO CARBON WITH ACTIVE WUSTITE PREPARED FROM ZN(II)-BEARING FERRITE

    T KODAMA, M TABATA, K TOMINAGA, T YOSHIDA, Y TAMAURA

    JOURNAL OF MATERIALS SCIENCE   28 ( 2 )   547 - 552   1993年1月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:CHAPMAN HALL LTD  

    CO2 decomposition reaction into carbon was studied at 300-degrees-C using the H-2-reduced Zn(II)-bearing ferrite which consisted of the Zn(II) oxide and the active wustite. The H-2-reduced Zn(Il)-bearing ferrite was prepared from Zn(II)-bearing ferrite by the reduction with H-2 gas at 300-degrees-C. The wustite (Fe(delta)O) in the H-2-reduced Zn(II)-bearing ferrite had a higher delta value (delta = 0.97, active wustite) than those of the normal wustites (0.90 &lt; delta &lt; 0.95) prepared at high temperatures ( &gt; 570-degrees-C). The decomposition reaction of CO2 proceeds in two steps: (1 ) CO2 reduction to CO, and (2) CO decomposition into carbon. In the initial stage, the reduction of CO2 into CO takes place, accompanying both the oxidation of the active wustite to the slightly oxidized wustite, and the transformation of active wustite and Zn(II) oxide into the Zn(II)-bearing ferrite. After the reaction of the initial stage attains equilibrium of an apparent state of rest, the adsorbed CO is decomposed into carbon, associated with the transformation of the slightly oxidized wustite and the Zn (II) oxide into the Zn (II)-bearing ferrite.

    DOI: 10.1007/BF00357836

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  • ADSORPTION OF CO2 ON OXYGEN-DEFICIENT MAGNETITE - ADSORPTION ENTHALPY AND ADSORPTION-ISOTHERM

    K NISHIZAWA, T KODAMA, M TABATA, T YOSHIDA, M TSUJI, Y TAMAURA

    JOURNAL OF THE CHEMICAL SOCIETY-FARADAY TRANSACTIONS   88 ( 18 )   2771 - 2773   1992年9月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    The adsorption isotherm and the enthalpy of adsorption of CO2 on oxides of oxygen-deficient magnetite have been studied by adsorption techniques. Oxygen-deficient magnetite was prepared by flowing H-2 gas through magnetite powder at 300-degrees-C. Adsorption of CO2 onto oxygen-deficient magnetite was studied in the temperature range 150-300-degrees-C. We found that the adsorption can be expressed by the Langmuir dissociative isotherm for three fragments: one carbon atom and two oxygen ions. Deposition of carbon after the adsorption reaction suggests that reduction of surface carbon seems to be involved in the adsorption reaction. The high reactivity for the reduction of CO2 to carbon is considered to come from such a reactive site where an electron is readily donated to the carbon of the CO2 molecule and the oxygen in the CO2 molecule is readily incorporated into a lattice point in the form of O2-. Electron hopping between the Fe2+ and Fe3+ ions in the spinel structure of the magnetite would facilitate the donation of an electron at the adsorption site. The distorted spinel structure of the surface of the H2-reduced magnetite, where the oxygen site is defected, would facilitate the incorporation of the oxygen of CO2.

    DOI: 10.1039/ft9928802771

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  • DECOMPOSITION OF CARBON-DIOXIDE TO CARBON WITH ACTIVE WUSTITE AT 300-DEGREES-C

    T KODAMA, K TOMINAGA, M TABATA, T YOSHIDA, Y TAMAURA

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY   75 ( 5 )   1287 - 1289   1992年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:AMER CERAMIC SOC  

    Active wustite (Fe(delta)O, with a delta-value of 0.98) was prepared by keeping normal wustite (delta-value of 0.94) in a N2 atmosphere at 300-degrees-C for 10 min. This reaction is given by (4-delta-2 - 3)Fe(delta-1)O --&gt; (4-delta-1 - 3)Fe(delta-2)O + (delta-2 - delta-1)Fe3O4 where delta-1 = 0.94 and delta-2 = 0.98. The equation indicates that the normal wustite undergoes eutectoid decomposition into active wustite and stoichiometric magnetite (Fe3O4). Carbon dioxide (1.013 x 10(5) Pa) was almost completely (100%) decomposed into carbon (zero valence) by the active wustite at the low temperature of 300-degrees-C, which was associated with the transformation of the active wustite into the stoichiometric magnetite. The internal pressure of the reaction cell eventually became a vacuum.

    DOI: 10.1111/j.1151-2916.1992.tb05574.x

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  • HIGH-VACANCY-CONTENT ZINC(II)-BEARING FERRITES FROM IRON(III) TARTRATE IN STRONGLY ALKALINE-SOLUTIONS

    T KODAMA

    JOURNAL OF MATERIALS CHEMISTRY   2 ( 5 )   525 - 528   1992年5月

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    記述言語:英語   掲載種別:研究論文(学術雑誌)   出版者・発行元:ROYAL SOC CHEMISTRY  

    Zn(II)-bearing ferrites with spinel-type structure have been synthesized in strongly alkaline solutions of iron(III) tartrate containing Zn(II) ions at 100-degrees-C. The Zn(II)-bearing ferrites contain few Fe(II) ions, but have a high cation vacancy content (high-vacancy-content Zn(II)-bearing ferrite). The ferrites are solid solutions represented by x(ZnFe2O4)-y(Fe3O4)-z(gamma-Fe2O3), where x + y + z = 1 (0.16 less-than-or-equal-to x less-than-or-equal-to 0.90, 0.01 less-than-or-equal-to y less-than-or-equal-to 0.02, 0.09 less-than-or-equal-to z less-than-or-equal-to 0.82). The cation vacancies are replaced with the Zn(II) ions in the reaction solution, and the replaced number increases with an increase in the concentration of the Zn(II) ions. The high-vacancy-content Zn(II)-bearing ferrites have an ultrafine particle size, &lt; 20 nm. The crystal growth of the ferrite particles is accelerated with the Zn(II) ions in the reaction solution.

    DOI: 10.1039/jm9920200525

    Web of Science

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  • High-vacancy-content ferrite with fine particles

    T. Kodama, T. Itoh, M. Tabata, Y. Tamaura

    Journal of Applied Physics   69 ( 8 )   5915 - 5917   1991年

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    記述言語:英語   掲載種別:研究論文(学術雑誌)  

    The high-vacancy-content ferrites represented by x(MFe2O 4)·y(Fe3O4)·z(γ-Fe 2O3), where x+y+z=1 (z≳0.50), were obtained in the clear and strongly alkaline solutions of Fe(III) and M(II) tartrate [M(II)=Zn(II), Ni(II), and Cd(II)] or dextrose at 100°C. The vacancies were replaced with the bivalent metal ions in the reaction solutions, and the replaced number increased with an increase in the concentration of the bivalent metal ions. The ferrite particle size was dependent on the bivalent metal species and the content (x,y). The Fe(II) ions enhanced the crystal-growth rate. The particle size of the magnetites (x=0) increased from 100 to 800 Å with an increase in the Fe(II) ion content (y=0.10-0.35). The high-vacancy-content magnetite was transferred from superparamagnetic to ferrimagnetic particles as the size increased. The Zn(II), Ni(II), and Cd(II) ions did not enhance the growth rate so much as compared to the Fe(II) ions. The particle sizes were less than 200 Å, and most of the particles were superparamagnetic. The saturation magnetizations were lower than the theoretical values, and increased with an increase in the particle size, indicating the surface effect.

    DOI: 10.1063/1.347838

    Scopus

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  • The Formation of High-vacancy-content M(II)-bearing Ferrites (M=Ni and Cd) from the Strongly Alkaline Solutions of Fe(III)-tartrate, and Dextrose (Jointly Worked)

    Ceramic Transactions   22   609   1991年

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  • Characterization of Zinc(II)-bearing Ferrites from the Strongly Alkaline Solutions of Fe(III)-tartrate, and Dextrose (Jointly Worked)

    Ceramic Transactions   22   603   1991年

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  • HIGH-VACANCY-CONTENT MAGNETITES AND ZINC-BEARING FERRITES FROM IRON(III) TARTRATE IN STRONGLY ALKALINE-SOLUTION

    Y TAMAURA, T KODAMA, T ITOH

    JOURNAL OF THE AMERICAN CERAMIC SOCIETY   73 ( 8 )   2539 - 2542   1990年8月

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    記述言語:英語   出版者・発行元:AMER CERAMIC SOC  

    DOI: 10.1111/j.1151-2916.1990.tb07631.x

    Web of Science

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書籍等出版物

  • Efficient thermochemical cycle for CO<sub>2</sub> reduciton with coal using a reactive redox system of ferrite

    Studies in Suface Science and Catalysis  1998年 

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MISC

講演・口頭発表等

  • Flowability and reactivity of spherical Mn-doped ceria particles for a solar thermochemical two-step water splitting by a fluidized bed reactor

    R. Kurosawa, T. Kodama, T. Kawamura, T. Nakano, S. Bellan

    Grand Renewable Energy 2022 International Conference (GRE2022)  2022年12月 

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    開催年月日: 2022年12月

    記述言語:英語   会議種別:口頭発表(一般)  

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  • 各種セビオライト中の炭酸塩の除去および不純物イオンの置換サイト

    粘土科学  2001年7月 

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    開催年月日: 2001年7月

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  • セピオライト結晶格子のMg(II)のCu(II)による水溶液中での置換反応(共著)

    北山 淑江, 村岡 雅弘, 児玉 竜也, 尾身 尚弘, 大泉 学

    粘土科学  1996年  日本粘土学会

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    開催年月日: 1996年

    記述言語:日本語  

    (1)球晶は前世紀の半ば頃に,その研究の萌芽をみて以来,一点を中心とする結晶外向成長の途上にある不安定な中問態の一型式とみなされた.生成環境相は濃厚系より希釈系に及び,結晶化度に幅があり(低いものは主に合成結晶,高いものは主に天然鉱物球晶),核形成よりみた系には,不均一に止らず均一系もある,全体を通じ,また部分を通じ,いくつかの共通性がある.これらを6.1に列挙した.(2)球晶の所定例について,上記の通性の中で重点を置き,球晶核とはなにかに視点を移し,成因に結びつけようとする報告がいくつかある.その骨子を紹介した(Morse and Donnay,Keller,Keith and Padden.(3)今世紀の中頃,結晶集合体に視点を置いた結晶化速度論の解析理論が出され(Avsami),これを受けて,高分子球晶の分野で,新しい解析理論と観察事実の整合が示され(Takayanagi),球晶の近代的研究の初期を迎えた.これらの概要を述べた.(4)希釈系の球晶の研究は,今日なお遅れている.将来の検討課題という意味で,結晶成長とコロイド系の様式の相剋の場という視点を書き添えて,この研究史観を終えた.

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産業財産権

  • 反応媒体および水素の製造方法

    児玉竜也

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    出願人:新潟大学

    出願番号:特願2023-161776  出願日:2023年9月

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  • 反応媒体および水素の製造法

    児玉竜也

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    出願人:新潟大学

    出願番号:特願2023-135908  出願日:2023年7月

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  • 水素の製造方法

    児玉竜也, 郷右近展之

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    出願人:新潟大学

    出願番号:特願2018-012060  出願日:2018年1月

    特許番号/登録番号:特許7037172  登録日:2022年3月 

    権利者:新潟大学

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  • 水の分解による水素製造法及び水素製造装置

    児玉竜也, 郷右近展之

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    出願人:新潟大学

    出願番号:特願2011-544265  出願日:2015年5月

    特許番号/登録番号:特許5739818  登録日:2015年5月 

    権利者:新潟大学

    特願2003-60101

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  • 内循環流動層を用いた水熱分解装置及び水熱分解法

    児玉竜也, 郷右近展之, 櫻井篤, 松原幸治

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    出願人:新潟大学

    出願番号:特願2012-018199  出願日:2012年1月

    特許番号/登録番号:特許5986589  登録日:2016年8月 

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  • 流動層を備えた太陽光集熱装置及びこれを用いた太陽光集熱方法

    松原幸治, 櫻井篤, 児玉竜也, 郷右近展之

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    出願人:新潟大学

    出願番号:特願2019-519197  出願日:2017年5月

    特許番号/登録番号:特許7061809  登録日:2022年4月 

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  • 集光太陽光の受熱装置、反応装置及び加熱装置

    児玉竜也, 松原幸治, 郷右近展之

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    出願番号:特願2016-519188  出願日:2014年5月

    特許番号/登録番号:特許6440267  登録日:2018年11月 

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  • 内循環流動層を用いた石炭コークスのソーラーガス化装置およびガス化法

    児玉竜也, 郷右近展之, 櫻井篤, 松原幸治

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    出願番号:特願2013-222867  出願日:2013年10月

    特許番号/登録番号:特許6232923  登録日:2017年11月 

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  • 太陽光を利用した集熱蓄熱装置

    児玉竜也, 郷右近展之, 松原幸治, 櫻井篤

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    出願番号:特願2014-534366  出願日:2012年9月

    特許番号/登録番号:特許6165743  登録日:2017年6月 

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Works(作品等)

  • Study on solar methane reforming and coal gasificatin to produce hydrogen

    2003年

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  • 反応性セラミックによる集光熱/水素エネルギー転換に関する研究

    1997年

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  • 新規膨潤性マイカのイオン交換に関する研究

    1997年

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  • 集光太陽熱による天然ガス改質・石炭ガス化による水素製造に関する研究

    1997年

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  • Study on solar thermochemical water splitting cycle

    1997年

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  • Study on nevel inorganic ion exchangers

    1997年

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受賞

  • 新潟日報文化賞 産業技術部門

    2021年11月   新潟日報社  

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  • 日本伝熱学会 11th SOLARIS会議 最優秀論文賞

    2021年9月   日本伝熱学会   セリアのソーラー流動層反応器による水素製造: 固気流体に関するEuler-Lagrange モデルによるの内循環流動層の最適化

    Selvan Bellan, Tatsuya Kodama, Hyun-Seok Cho, Jin-Soo Kim

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  • 平成22年度日本エネルギー学会 進歩賞(学術部門)

    2011年2月   日本エネルギー学会   高温太陽集熱による水熱分解ソーラー水素製造技術の開発

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  • アメリカ機械工学会 太陽エネルギー部会 最優秀論文賞

    2005年8月   アメリカ機械工学会(ASME)   ソーラー改質レシーバ反応器のためのRu/Ni-Mg-O 触媒 SiC 発泡吸収体

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  • 財団 手島工業教育資金団工業技術研究賞

    2002年  

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    受賞国:日本国

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  • 第70春季年会講演奨励賞

    1996年  

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    受賞国:日本国

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共同研究・競争的資金等の研究

  • 太陽集熱利用型CO2‐H2O共熱分解サイクルによる合成ガス製造

    研究課題/領域番号:20H00362

    2020年4月 - 2024年3月

    制度名:科学研究費助成事業

    研究種目:基盤研究(A)

    提供機関:日本学術振興会

    児玉 竜也, Bellan Selvan, 長瀬 慶紀, 石井 知彦, 曹 賢石

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    配分額:44850000円 ( 直接経費:34500000円 、 間接経費:10350000円 )

    1.流動層反応器試験用に必要な量の高活性ドープセリアの微粒子をスプレードライ法で製造した。流動性に優れた真球状微粒子として製造することができた。反応性も共沈法で合成してきたドープセリアと同等であり、非ドープセリアと比較して3~4倍の活性が得られた。
    2.並行して、さらなる高活性酸化還元金属酸化物の探索を行い、鉄系の高エントロピー酸化物において、ドープセリアよりも、さらに高活性の金属酸化物を見出した。
    3.宮崎大学に設置している太陽集光システムで、集光エネルギー量の測定を行ったところ、地上反射鏡の経年劣化が原因と思われる太陽集光エネルギー量の著しい減少が観測された。これまでの流動層反応器の設計では太陽集光の照射しても反応温度にまで金属酸化物の温度をあげられないことが予想された。この状況に対応するためには、流動層型のみならず、移動層型反応器にも設計範囲を広げて、大型ソーラー反応器の設計を見直すことが必要となった。しがたって、ソーラー反応器数値解析モデル等により、流動層から移動層利用も含めた大型ソーラー反応器の再設計を行うこととした。

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  • 低温反応活性セラミックによる太陽集熱水熱分解水素製造システムの開発

    研究課題/領域番号:17H01376

    2017年4月 - 2020年3月

    制度名:科学研究費助成事業

    研究種目:基盤研究(A)

    提供機関:日本学術振興会

    児玉 竜也, 長瀬 慶紀, 石井 知彦, 清水 忠明, Bellan Selvan, 曹 賢石, 金子 宏

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    配分額:43680000円 ( 直接経費:33600000円 、 間接経費:10080000円 )

    高温の太陽集熱(1100~1500℃)を利用し、反応性セラミックの酸化還元系による2段階水熱分解サイクルによって水素を製造する反応システムとして、大型用(0.5-50MWth)の粒子流動層式と、小型用(50kWth)の発泡体デバイス式の、2つの反応システムのプロトタイプを、3-100kWthの反応器試験等と数値解析から設計した。低温活性型反応性セラミックのマンガンドープセリア等を利用して、流動層反応器用には流動性の優れた真球状微粒子を、デバイス式反応器用には円錐型発泡体デバイスを合成し、従来のベンチマークである非ドープセリアのものを大きく上回る反応活性を持たせることに成功した。

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  • ソーラー試験による熱-光ハイブリット活性水分解デバイスの創製

    研究課題/領域番号:16K14056

    2016年4月 - 2018年3月

    制度名:科学研究費助成事業

    研究種目:挑戦的萌芽研究

    提供機関:日本学術振興会

    児玉 竜也

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    配分額:3770000円 ( 直接経費:2900000円 、 間接経費:870000円 )

    太陽集熱をエネルギー源として運転される二段階水熱分解サイクルにおいて反応媒体となる反応性セラミック(酸化還元金属酸化物)に、光半導体特性を有する金属酸化物をドープし、これを用いて発泡体構造の反応デバイスを作製する。これを可視光照射によって反応試験することにより、従来よりも低温において作動する「熱‐光ハイブリッド活性型反応性セラミックデバイス」の創成を目指した。熱活性の高いセリウム酸化物(セリア)と、光触媒活性を持つ鉄酸化物の固溶体を担持した小型の発泡体デバイスをサンシミュレータからの疑似太陽集光で試験した結果、従来の1500℃よりも低い1300℃のサイクルで、セリアを上回る活性が見出された。

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  • ソーラー試験による太陽集熱水分解水素製造システムの開発

    研究課題/領域番号:26249151

    2014年4月 - 2017年3月

    制度名:科学研究費助成事業

    研究種目:基盤研究(A)

    提供機関:日本学術振興会

    児玉 竜也, 金子 宏, 松原 幸治, 清水 忠明, 郷右近 展之, 松葉 正, 横田 昌久, 吉田 一雄

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    配分額:40560000円 ( 直接経費:31200000円 、 間接経費:9360000円 )

    世界のサンベルト地域で太陽集熱によって水を分解して水素を製造する反応システムのプロトタイプの開発を目指し,金属酸化物(反応性セラミック)を媒体とする2段階水熱分解サイクルを用いた2つのタイプのソーラー反応器(円錐型発泡体デバイス式および粒子流動層式)の開発を行った.これらソーラー水熱分解反応器の原理で水素製造が可能であることを,30~40kWth反応器のソーラー試験で立証した.両反応器の実用化の設計概念を検討した結果,流動層式反応器は1サイクル当たりの水素製造能が大きいことかMWth級システムでの実用化に,発泡体式反応器は500kWth程度の小型システムでの実用化に適していることが見出された。

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  • 高効率太陽熱発電のための高温型粒子流動層式ソーラー集熱/蓄熱システムの開発

    研究課題/領域番号:25289357

    2013年4月 - 2016年3月

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    松原 幸治, 長瀬 慶紀, 平元 和彦, 児玉 竜也, 櫻井 篤

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    配分額:17420000円 ( 直接経費:13400000円 、 間接経費:4020000円 )

    本研究では、高効率太陽熱発電のための粒子流動層式集熱/蓄熱システムの研究開発を行なった。流動層式集熱器/反応器の研究において、集光照射した円筒式流動層の集熱実験によって1000℃以上の高温粒子と高温空気が得られることが示された。このため本研究では、流動層式集熱器の数値解析技術の構築と組織的循環を伴う流動層の集熱実験を行い、高温型集熱/蓄熱に有用な新型流動層を提案した。この新型流動層は、これまでの二塔式内循環流動層を基本としながら、連続的な粒子の供給と排出を可能としたものである。その流動の様子を可視化実験し、新型流動層の粒子の外的な循環によって集熱/蓄熱システムに応用可能であることを確認した。

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  • 炭素資源の直接光照射式ソーラーガス化反応器の開発

    研究課題/領域番号:22560836

    2010年 - 2012年

    制度名:科学研究費助成事業

    研究種目:基盤研究(C)

    提供機関:日本学術振興会

    籏町 剛, 児玉 竜也, 児玉 竜也

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    配分額:4420000円 ( 直接経費:3400000円 、 間接経費:1020000円 )

    サンベルトでのビームダウン太陽集光システムでの利用を想定した石炭やバイオマスなどを原料とするソーラーガス化反応システムの構築を目的として、ラボスケールの直接採光式の流動層反応器をステンレスで作製し、石炭コークスおよび褐炭を用いてその有用性を検討した。ガス化反応試験はキセノンアーク灯(放射束3キロワット)によるサンシミュレータにより上部より照射しながらバッチ式で行った。実験の結果、反応器の採光口以外の断熱,水蒸気改質の場合は反応器内へ導入する水蒸気濃度を高くすることが反応速度を向上させるのに効果的であることがわかった。また、流動コークスが反応器内を循環しやすいよう、ドラフト管を取り付けてその内外でガスの線流速を変えることで、コークス温度が均一になり反応域が広がり反応速度が増した。それに併せて、コークスの流動性を上げるための工夫を凝らしたところ、さらに反応性が向上し、光/化学エネルギー転換効率は最大13パーセントときわめて高い値を記録した。

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  • 熱-光ハイブリット活性水分解デバイスの創製とそのソーラー試験

    研究課題/領域番号:22656215

    2010年 - 2011年

    制度名:科学研究費助成事業

    研究種目:挑戦的萌芽研究

    提供機関:日本学術振興会

    児玉 竜也

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    配分額:3560000円 ( 直接経費:3200000円 、 間接経費:360000円 )

    本研究では,従来の高温太陽集熱をエネルギー源とする二段階水熱分解サイクルの反応媒体である水熱分解性セラミックの熱活性に,光半導体触媒の光活性を添加し,通常1000℃以上でしか作動しないサイクル反応を低温化することに挑戦する。すなわち熱-光ハイブリット活性型の反応性セラミックデバイスの創製に挑戦する。22年度は下記の研究成果が得られた。
    研究代表者が開発したFe含有立方晶ジルコニアをゾルーゲル法で合成し,その際にセリウム等の光触媒金属酸化物を添加した反応性セラミック微粉体を合成した。この微粉体をスピンコート法でジルコニア,あるいはSiCのセラミッレ発泡体に担持し,反応デバイスの作製を行なった。この新規反応デバイスを3kW太陽炉シミュレータからの擬似太陽集光照射下で反応試験を行った。セリウムを添加しない反応デバイスと反応温度が低温化しているかを比較検討して結果,反応性セラミックの二段階反応の2つの反応,すなわち熱還元反応と水分解反応のうち,水分解反応について,従来の反応デバイスと比べて顕著な低温化が起こっていることが見出された。セリウムを添加しない場合は1100℃以上を必要としていたが,セリウムを添加すれば600~800℃でも十分に反応を行えることが見出された。後は,もう一つの反応の熱還元反応を低温化することができれば二段階反応全体を低温化することが出来る。これにはニッケル,コバルト酸化物等の添加が有効と考えられた。

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  • 反応性セラミックによる水熱分解ソーラー反応器の開発

    研究課題/領域番号:21360478

    2009年 - 2011年

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    児玉 竜也, 郷右近 展之

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    配分額:19110000円 ( 直接経費:14700000円 、 間接経費:4410000円 )

    本研究では,世界のサンベルト地域で得られる1000~1500℃の高温太陽集熱をエネルギー源として反応性セラミックによる二段階水熱分解サイクルによってソーラー水素の製造を行う2つの異なるコンセプトのソーラー反応器(発泡体デバイス型反応器および内循環流動層型反応器)のプロトタイプを3~5kWで作製し,これを太陽炉シミュレータあるいはパラボラディッシュ型太陽集光器(韓国インハ大学所有)を用いて性能評価することを目的とする。22年度は下記の研究成果が得られた。
    1)発泡体デバイス型反応器については下記の成果が得られた。
    発泡体デバイス反応器の2号器を作製し,新潟大の3kW太陽炉シミュレータによる擬似太陽集光による試験と,韓国インハ大学の5kWディッシュ型太陽集光器でのフィールド試験を並行して行った。反応体である発泡体でデバイスの反応性セラミック担持量等の合成条件を検討することにより,従来よりも発泡体デバイスの耐久性を向上させこの反応システムにおいて二段階水分解反応のサイクル化を行なうことが出来た。
    2)内循環流動層型反応器については下記の成果が得られた。
    内循環流動層反応器については,二段階サイクル反応を一段階プロセスとして実施できる従来にない画期的な反応器を考案している。,より安定に水素生成を行なうことを目的として反応器の設計改良を行い,これを新規に導入した5kW太陽炉シミュレータにより擬似太陽集光による性能試験を行った。同時に流動層に用いる反応性セラミック粒子の改良も行った結果,従来よりも一段階プロセスとして安定・定常的に水素生成を維持することに成功した。これに関しては国際特許出願を行なった。

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  • 低温水分解能を持つ熱-光ハイブリット活性セラミックデバイスの開発

    研究課題/領域番号:20656155

    2008年 - 2009年

    制度名:科学研究費助成事業

    研究種目:挑戦的萌芽研究

    提供機関:日本学術振興会

    児玉 竜也, 郷右近 展之

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    配分額:3600000円 ( 直接経費:3600000円 )

    本研究では,従来の高温太陽集熱をエネルギー源とする二段階水熱分解サイクルの反応媒体である水熱分解性セラミックの熱活性に,光半導体触媒の光活性を添加し,水熱分解サイクル反応を低温化することに挑戦した。初年度の研究により,研究代表者が見出した水熱分解性セラミックのFe_3O_4/ジルコニア担持体(Fe含有立方晶ジルコニア,あるいはFe_3O_4/単斜晶ジルコニア)にNiOをドープした水熱分解性セラミック粉体合成に成功し,さらにスピンコーティング法等の方法を応用して,この粉体を材料とした小型発泡体デバイスを作製することにも成功した。さらに,擬似太陽集光を直接デバイスに照射して2段階水分解反応を行う反応デバイスの活性試験を行い,NiOドーブによりデバイスの反応活性が向上することを確認した。今年度は下記の研究を実施する。今年度は下記の研究成果を得た。
    1)作製の成功したFe-Ni含有立方晶ジルコニア発泡体デバイスについて,立方晶ジルコニアに対するNiOドープ量,またFeOドープを変化させ,反応デバイスの反応活性の向上を試みた。反応試験を太陽炉シミュレータで行い,FeO:NiO=2:1のドープ量が反応活性に対して最適なドープ量であることを見出した。
    2)NiO同様に熱力学的見地,および光半導体活性の見地からCoOがFe_3O_4/ジルコニア担持体の反応活性を熱-光ハイブリット活性化によって高めると期待されるため,同様の手法でCoOをドープしたFe_3O_4/ジルコニア担持体粉体を合成し,その水熱分解活性を,赤外線イメージ炉を熱源として試験した。反応活性はほぼNiOドーブ型と同様の活性を得ることが出来た。

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  • 高水熱分解性セラミックとその反応デバイスの開発

    研究課題/領域番号:19360436

    2007年 - 2008年

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    児玉 竜也, 郷右近 展之

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    配分額:20150000円 ( 直接経費:15500000円 、 間接経費:4650000円 )

    本研究では, 海外のサンベルトの大型集光システムで得られる1400~1 600℃の高温太陽熱を熱源として2段階水熱分解サイクルを行う高水熱分解性セラミック(微粉体)の開発と, その反応デバイス化を目的とした。研究成果として, (1) 研究代表者が見出したフェライト/ジルコニア反応体(微粉体)を基軸として, 水熱分解性セラミック微粉体を, 米(サンディア国立研究所)で開発中のロータリー型分解器と, 日本・韓国(新潟大学・インハ大学)で開発中の発泡体デバイス水分解器のそれぞれのソーラー水分解器の反応体として適応するように改良し, その反応性とサイクル反応性を向上させることに成功した。サンディア国立研究所では, これらの結果からこの新規反応体によるデバイス開発を始めた。
    (2) 一方で, これを日本・韓国(新潟大学・インハ大学)で開発中の新型の発泡体デバイス反応器に利用できるように反応デバイス化し, その発泡体デバイスで2段階水熱分解サイクルを連続的に繰り返し行うことに成功した。反応活性と安定性の両面から総合的に判断すれば, 本反応デバイスは現在最も性能の優れた水熱分解デバイスであると評価できる。さらに韓国(インハ大学)の5kW太陽炉でこの反応デバイスのフィールド試験を行うための大型デバイスを合成すると共に, フィールド試験用のソーラー反応器を設計した。

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  • 熱-光ハイブリット活性セラミックによる低温水分解反応の開発

    研究課題/領域番号:18656274

    2006年 - 2007年

    制度名:科学研究費助成事業

    研究種目:萌芽研究

    提供機関:日本学術振興会

    児玉 竜也, 清水 研一

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    配分額:3500000円 ( 直接経費:3500000円 )

    本研究では,高温(1400℃)で進行する反応性セラミックによる2段階水熱分解サイクル反応を,半導体の光化学的効果を他金属ドープで反応性セラミックに添加するという手法で低温化する試みを行った。これを研究代表者が見出した水熱分解性セラミック「Fe^<2+>-Fe^<3+>含有型立方晶ジルコニア」で検討した。すなわち,反応性セラミックを反応デバイス化し,これに擬似太陽集光を直接照射して行う活性試験と,反応性セラミックの固体化学的・光触媒化学的な構造解析によるアプローチを併用して,低温水分解性セラミックの開発を行った。19年度は下記の研究成果を得た。
    (1)1400℃における水素発生量増大化の検討:デバイスへの反応性セラミック担持量を増大することを目的に,スピンコート法へ担持法を変更した。担持プロセスを大幅に簡便化でき,鉄酸化物を約10wt%担持量するために数十回を要していた繰り返し担持を数回で到達できるようになり,担持量を増大させることが容易になった。1100-1400℃の水分解試験の結果,反応性セラミック粉末試料の熱活性のみの場合と比較して1.2倍に水分解活性が向上することが見出された。粉末試料の方が反応デバイスと比較して反応表面積が大きく,高活性が得られるはずであるが,逆の結果が得られたことは,期待通りに光触媒効果が関与して活性を向上させていることを示唆している。
    (2)低温化の検討:担持量を増大させたデバイスでは水素発生量は増大したが,焼結が起きやすくなり反応温度は1200-1500℃とむしろ増大した。一方,鉄酸化物の粉末試料ではあるが,予めNiとMnをドープすると1400℃の反応活性が増大することが見出され,この手法で1400℃以下の反応活性も向上できると考えられる。

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  • 連続二段階水分解反応装置による集光太陽熱のソーラ水素転換技術の開発研究

    研究課題/領域番号:17206100

    2005年 - 2006年

    制度名:科学研究費助成事業

    研究種目:基盤研究(A)

    提供機関:日本学術振興会

    玉浦 裕, 芳澤 善男, 金子 宏, 長谷川 紀子, 児玉 竜也, 中島 啓光, 布施 明徳

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    配分額:50700000円 ( 直接経費:39000000円 、 間接経費:11700000円 )

    1kWロータリー反応炉で単純な3工程運転の可能性を見出し、これに基づき10kWローター反応炉の設計・試作を行った。さらに実用化に向けた50kW回転反応炉の開発設計にはビームダウン集光系の地上焦点のフラックス分布を検討する必要があり、そのためのシミュレーター開発を行った。また、多重リング型タワー反射鏡を用いたビームダウン方式における集光flux分布計算手法を開発し、CGと連携させるビームダウン集光システムの3D表現化のCGソフト開発を行った。これらを基にして自己姿勢認識型ヘリオスタットの実用化規模の1/5スケール(2mx2m)の設計・試作を行った(特許出願)。2年目は前年度に開発したロータリー反応炉のスケールアップ開発を目的として、二号機(ローター直径50cm)の設計・開発・試作を行い、ニッケルフェライトによる性能試験を行った。その結果、ニッケルフェライトに集光ビーム(赤外イメージ炉)を急速照射すると非平衡状態でFrenkel欠陥フェライトが反応中間体として形成し、高酸素分圧下(空気中)において酸素放出してカチオン過剰型スピネル構造を形成することから集光太陽熱を吸熱化学反応に利用してカチオン過剰型スピネル構造を経由するソーラー水素生産の実用への道を開いた。さらに高温耐熱性能のある反応性セラミックスとしてYSZおよび酸化ジルコニウムをベースとした固溶体を合成し、これらが二段階水分解プロセスを熱安定運転できることを明らかにした。集光システムとしては東工大式ビームダウン集光システムの開発を進め、(1)多重リング中央反射鏡を用いた集光システムのシミュレーター、(2)20MW太陽熱発電システムの設計、(3)集光システム用クロスビーム型ヘリオスタットの設計・試作、を行った。さらに、さらにこれらの開発技術)をソーラーハイブリッド燃料生産システムとしての実用化を目指し、オーストラリアCSIROとの国際共同開発AP6プロジェクトを立ち上げた。

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  • 高温太陽熱水分解のための反応性セラミックデバイスの開発

    研究課題/領域番号:17360463

    2005年 - 2006年

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    児玉 竜也, 郷右近 展之, 清水 研一

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    配分額:14500000円 ( 直接経費:14500000円 )

    サンベルトで得られる高温太陽熱を利用し、水の熱分解で水素を製造する二段階水分解サイクルに必要とされる反応性セラミックデバイスの開発を行い、下記の研究成果を得た。
    1.高反応性セラミック微粉体の開発
    反応性セラミックとして研究代表者が開発したフェライト/ジルコニア担持体について他金属ドープ効果を比較し、高活性のNi_<1.0>Fe_<2.0>O_4/ZrO_4を見出した。一方、研究代表者は、担体を単斜晶ジルコニアから、イットリウム含有量が8mol%以上の立方晶安定化ジルコニア(YSZ)に替えると、熱還元反応においてFe^<2+>含有立方晶ジルコニアが生成し、低温水分解反応ではこれが水蒸気と反応して水素を生成しフェライトではなくFe^<3+>含有立方晶ジルコニアを生成するという新しいサイクル反応機構を見出した。
    2.反応デバイスの合成と反応試験
    Ni_<1.0>Fe_<2.0>O_4/ZrOとFe_3O_4/YSZの2つの微粉末反応体をそれぞれジルコニア発泡体に担持したデバイスを作製し、反応性を検討した結果、熱還元温度1400℃、水分解温度1100℃の2段階サイクル反応で13-30サイクル以上の水素発生が観測された。しかし、次第にデバイスの亀裂が起こった。そこで熱耐久性の高いSiC発泡体をマトリックスとすることとした。
    3.SiC発泡体のジルコニア被覆と太陽光照射耐久試験による性能評価
    熱力学計算からSiC発泡体をFe_3O_4に対して不活性のジルコニアで被覆することが必要であることが見出されたため、スピンコート法によりこれを検討し、良好なジルコニア被覆をすることができた。一方、SiC発泡体マトリックスについては、太陽炉による太陽光照射下試験で良好な熱耐久性を有することが確認された。

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  • 光-熱ハイブリット活性型水分解性セラミックの開発

    研究課題/領域番号:15656243

    2003年 - 2004年

    制度名:科学研究費助成事業

    研究種目:萌芽研究

    提供機関:日本学術振興会

    児玉 竜也, 清水 研一

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    配分額:3400000円 ( 直接経費:3400000円 )

    本研究は従来の反応性セラミックによる1500℃付近における2段階水分解熱化学サイクル,
    M_xO_y=M_xO_<y-δ>+δ/2O_2 (高温酸素放出反応)
    M_xO_<y-δ>+δH_2O=M_xO_y+δH_2 (低温水分解反応)
    の反応系に、紫外-可視光応答性のある光半導体を導入して反応温度を低温化させる新しい「光-熱ハイブリット活性型反応性セラミック」を開発することを目的とする。本年度は下記の成果を得た。
    1.反応試験用試料として反応性セラミックをディスク状のセラミック発泡体に担持した反応デバイスの作製を行った。光半導体で高温安定なSiCとZrO_2の発泡体を作製し、これにNiFe_2O_4/ZrO_2微粉体の反応性セラミックを担持した。石英窓付き反応器に設置し、模擬太陽集光を直接照射して1400℃に加熱し、光-熱ハイブリットによる活性化を試みた。この反応デバイスによる反応器は大型化も可能な設計であり、従来にない独特な方式と評価できる。
    2.反応デバイスの構造変化を追跡し、ZrO_2発泡体のデバイスでは1400℃の活性化によりNiFe_2O_4を活性相のNi_<1/3>Fe_<2/3>Oへ還元できることを確認した。1000℃で水分解反応を行うと、水素を発生してNi_<1/3>Fe_<2/3>OがNiFe_2O_4へ再酸化され、サイクル反応が可能であることが見出された。
    3.熱でのみ活性化を行った場合の反応効率を上回る結果は見られなかったが、これは、模擬太陽光照射下ではデバイスの温度分布が大きいため熱活性を十分に引き出せず、また光照射面積が十分でないことから光活性も十分に発現されてないことが要因と推察した。
    4.今後は、本研究の成果を踏まえ、光照射が反応性セラミック粒子全体にいき渡る粉体流動層系で、光-熱ハイブリット活性化を検討することとし、試験用の石英窓を備えた流動層反応器を作製した。

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  • 集光太陽光反応性セラミックスによるソーラー水素生産技術の開発研究

    研究課題/領域番号:15206112

    2003年 - 2004年

    制度名:科学研究費助成事業

    研究種目:基盤研究(A)

    提供機関:日本学術振興会

    玉浦 裕, 末包 哲也, 伊原 学, 金子 宏, 長谷川 紀子, 児玉 竜也

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    配分額:47060000円 ( 直接経費:36200000円 、 間接経費:10860000円 )

    ニッケルフェライト系を反応性セラミックスとする酸素放出反応用の太陽反応炉の開発に向け、1473-1773Kでの温度スイングによる二段階水分解過程が繰り返し進行させることに成功した。亜鉛フェライト系においては、ZnO+Fe_3O_4粉体混合物として回収するリサイクルシステムを実用化に向けた太陽反応炉の設計コンセプトとして考案し、この開発に必要な擬似高温太陽熱(空気気流中1873K)を供給できる装置を用いて、落下速度を制限することにより反応性を高める研究を行った。この反応炉では、酸素放出過程を1573K付近に低温化させて開発を進めることが可能であるとの見通しを得た。また、固定床型太陽反応炉として水蒸気流通による水分解過程と赤外照射による酸素放出過程とを連続して繰り返し行うことが出来る回転式シリンダー型反応炉を設計試作した。このシリンダー型反応炉は二段階水分解過程を高効率で進行させ得る画期的な反応炉であることを確認した。
    タワー式集光プラントの光学設計を行い、実質2000の集光倍率を必要とする場合は約2700倍の集光特性が必要であるが、太陽高度が高い場所では、3000倍の集光倍率は得られることが分かった。またYSZ(Fe,Ni)は反応初期に急速に酸素放出を起こし、高フラックス太陽熱に対応できる酸素放出反応性を有することを明らかにした。2000kW/m^2のフラックスに対応して、吸熱反応が進行する場合、6.22mol/m^2となりYSZ01NFは固定反応床を用いるデュアル反応室型太陽反応炉において固定反応床の厚みを数センチにできることが分かった。このよう今回開発したYSZ01NF系の反応性セラミックスとデュアル反応室型太陽反応炉の組み合わることにより、集光太陽熱の高フラックスに対応する太陽エネルギー/化学エネルギー変換によるソーラー水素生産の可能性が見いだされた。

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  • 高/中温での太陽集熱による水素製造触媒デバイスの開発

    研究課題/領域番号:15360509

    2003年 - 2004年

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    児玉 竜也, 清水 研一, 安藤 秀征, 佐藤 信博, 水野 修

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    配分額:12900000円 ( 直接経費:12900000円 )

    中・高温の太陽集熱を水素に転換する下記の2つの反応プロセスについて新規触媒デバイスの開発を行った。
    1.高温(1000〜1500℃)用の反応性セラミックによる水の熱分解サイクル
    M_xO_y=M_xO_<y-δ>+δ/2O_2(高温酸素放出反応)
    M_xO_<y-δ>+δH_20=M_xO_y+δH_2(低温水分解反応)
    高活性微粉体で発泡構造体に担持可能な反応性セラミックの開発を行い、さらに、微粉体をセラミック発泡構造体に担持し触媒デバイス化を行った。
    1)高活性反応セラミックとしてフェライト/単斜晶ジルコニア担持体を見出しており、Fe_3O_4⇔FeOの相転移が担体上で起こり水分解が進行する。活性を向上させるドープ種を検討し、Niドープで高い反応効率(70%)が達成できた。
    (2)フェライト/立方結晶ジルコニア担持体では、FeO固溶型ジルコニアが生成し、これが水分解に寄与するという新しい反応機構が発見された。この機構により鉄酸化物の融解・焼結による失活が回避され、サイクル反応性が向上することが見出された。
    (3)反応性セラミックをSiC、及びZrO_2発泡構造体に20wt%以上担持した触媒デバイスを作製することができた。今後は本研究の成果を踏まえ、デバイスの反応試験を行う。
    2.中温(500〜1000℃)用の天然ガス(メタン)の吸熱改質反応による水素製造
    CH_4+2H_2O=3H_2+CO_2(吸熱メタン改質触媒反応)
    Ru/Al_2O_3担持Ni-Cr-Al合金発泡体触媒デバイスを高活性化する合成条件を見出した。さらに14cm径に大型化し、大型太陽炉で集光照射し、デバイスの熱的な特性評価を行った。従来のセラミック発泡体によるものと比較し、より高い熱伝導性を持つことからデバイス中心のオーバーヒートが回避され、全体に渡ってより均一な温度分布が達成されることが見出された。これは反応・エネルギー効率向上に大きく寄与する。

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  • 太陽熱/化学燃料転換のための低温作動型メタン改質触媒デバイスの開発

    研究課題/領域番号:13780404

    2001年 - 2002年

    制度名:科学研究費助成事業

    研究種目:若手研究(B)

    提供機関:日本学術振興会

    児玉 竜也

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    配分額:700000円 ( 直接経費:700000円 )

    吸熱反応であるメタンの二酸化炭素改質反応(CH_4+CO_2→2CO+2H_2)に集光太陽熱をプロセスヒートとして吸収させることで、製造燃料の持つエネルギーを原料メタンと比較して25%程度、太陽エネルギーによって増大させることが可能である。触媒を担持したセラミック発泡体プレート(触媒デバイス)に集光を直接照射し、これに反応ガスを流通して改質を行う大型のソーラー改質器が、欧米で既に開発されているが、この改質器を日本等の温帯地域で有効に利用するには、さらに高活性の触媒デバイスが必要である。本研究では、従来のセラミック発泡体に替えて、熱伝導効率の高い金属発泡体をデバイスに使用することが有効と考え、検討を行った。今年度は、昨年度に開発したRu/γ-Al_2O_3担持型Ni-Al-Cr合金発泡体(高温耐久性)の触媒デバイスについて合成条件を検討し、反応活性をさらに向上させることができた。今年度の研究成果の総括として、下記の2点が見出された。
    1)本研究のRu/γ-Al_2O_3担持金属発泡体は、太陽集光のエネルギー密度が低い場合に従来のRu/γ-Al_2O_3担持セラミック発泡体を超える反応効率を実現する。集光のエネルギー密度が200kW/m^2程度のとき、従来の触媒デバイスではエネルギー転換率が高々45%程度であるのに対し、本研究の金属発泡体触媒デバイスでは70%を超えるエネルギー転換率を達成することができた。コスト的にも高価なRhに替えて、より安価なRuを使用できるので触媒デバイスのコストダウンができる。
    2)本研究の金属発泡体触媒デバイスは、集光のエネルギー密度が高い場合においても、そのエネルギー分布が不均一なときに、従来のセラミック発泡体よりも高い反応効率を実現する。
    これらの特性は金属発泡体の良熱伝性によるものと考えられる。200kW/m^2の集光エネルギー密度は、日本等の温帯地域で1000倍程度の集光で容易に達成できる。実用化のためには、今後、本反応デバイスの大型化による反応試験が必要である。

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  • 集光熱反応性セラミックスを用いるソーラ水素生産に関する研究

    研究課題/領域番号:12308022

    2000年 - 2001年

    制度名:科学研究費助成事業

    研究種目:基盤研究(A)

    提供機関:日本学術振興会

    玉浦 裕, 辻 正道, 金子 宏, 児玉 竜也

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    配分額:40800000円 ( 直接経費:37800000円 、 間接経費:3000000円 )

    前年度(平成12年度)に、太陽エネルギー/水素生産サイクルシステムの二相分解性反応性セラミックス系として、Zn-フェライト系を用いることで酸素放出反応としてはかなり低温(1300C)で進行することを見出したことに基づき、この系の酸素放出過程について実用化に向けた太陽反応炉を試作し、擬似集光太陽ビームとしてキセノンビームを用いた性能評価実験を行った。また、低温化できた理由として、ZnOがスピネル構造のAサイト選択性によるものと判断し、マンガンフェライト系による二相分解性反応性セラミックス系について反応性を検討し、ZnO/マンガンフェライト系において1000℃付近まで低温化出来ることを見出した。この系では酸化物固体相での相変換によるリサイクルシステムが可能であり、このリサイクルシステム用としての反応炉の概念設計を行い、実験によりその可能性を確認した。平成13年11月にオーストラリアで開かれた国際太陽エネルギー会議(研修出張)でこれらの内容を発表すると共に、本研究のオーストラリア大学との共同研究について打ち合わせを行い、反応炉の改良設計を行った(現地での実験は来年度に予定)(今年度は海外出張費は不使用)。前年度にビームダウン型集光装置のヘリオスタット面積及びフレネルレンズ面積を2倍に改良したものについて、集光光度測定器を用いて集光効率を正確に測定し、集光分布と集光システムの関連について検討した。さらに、太陽光をより正確に追尾する為にヘリオスタットの追尾架台をあらためて設計しなおして作成し、ヘリオスタットの日本独自技術の開発に向けた設計概念に対する開発課題の抽出を行った。また、改良した装置を用いて実際にZnO/マンガンフェライト系による性能評価実験を行い、太陽化学エネルギー変換効率による水素生成の可能性のあることを実証した。

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  • 有機酸水溶液中での粘土層間チタニア架橋体の合成と機能材料への応用

    研究課題/領域番号:11555235

    1999年 - 2001年

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    北山 淑江, 木島 嘉之, 松田 泰宏, 児玉 竜也

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    配分額:10400000円 ( 直接経費:10400000円 )

    従来、粘土層間チタニア架橋体の合成は、塩酸溶液で行われていたが、塩酸は反応性が高く金属を腐食するため反応容器の材料が制限されたり、周辺装置の腐食が問題となり使用に際しては環境への配慮を行う必要があった。
    本研究では、環境にやさしい合成法として腐食性の弱い酢酸を用いて、各種粘土をホストとして、粘土層間チタニア架橋体の合成に成功した。合成した粘土層間チタニア架橋体の機能材料への応用研究に一環として、光触媒作用、紫外線遮蔽剤への応用のため基礎実験を行った結果、次のことが明らかになった。
    (1)粘土層間チタニア架橋体は水中の難分解性残留塩素系農薬の完全分解応用高活性光触媒となることを発見した。従来、難分解性残留塩素系農薬であるHCH(通称BHC)の光分解に対してTiO_2は不活性といわれてきた。本研究で合成した雲母のチタニア架橋体(TiO_2-pill-Mica)がHCHの光照射によるCO_2とHC1への完全分解に高活性を示し、その原因がTiO_2を疎水性粘土をホストとして粘土架橋体し、HCHの吸着能の向上させたことによることを証明した。
    (2)ベンゼンの部分酸化反応に粘土層間チタニア架橋体は触媒作用を示し、そのホストとなる粘土の種類により生成物が異なることがわかった。水の共存下、TiO_2-pill-MicaおよびTiO_2-pill Saponite触媒を用いるとマレイン酸が主生成物となり、TiO_2-pill Monmorilloniteではレゾルシンが生成した。
    (3)粘土層間チタニア架橋体は添加される母材を保護する有用な紫外線遮蔽剤として使用できる可能性をもつことが明らかになった。チタニアを紫外線遮蔽剤として用いる場合、添加される母材の光分解による変質が問題となっている。本研究では、粘土層間チタニア架橋体の化粧品への添加を想定し、油脂の基本構造モデルとして分子サイズの異なるカルボン酸の光分解反応を行った。粘土層間TiO_2架橋体のうちTiO_2-pill Saponiteがカルボン酸に対して最も不活性であることから、紫外線遮蔽剤として適していることがわかった。

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  • 太陽熱/化学エネルギー低温転換を目指した太陽光石炭ガス化触媒の開発

    研究課題/領域番号:11780365

    1999年 - 2000年

    制度名:科学研究費助成事業

    研究種目:奨励研究(A)

    提供機関:日本学術振興会

    児玉 竜也

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    配分額:2100000円 ( 直接経費:2100000円 )

    本研究は、集光太陽熱を化学エネルギー(化学燃料:CO及びH_2)へ高効率で転換する、二酸化炭素による石炭のソーラーガス化システムを構築することを目的として、太陽光石炭ガス化反応に高活性を示す触媒の開発を行うものである。触媒には、石炭灰からの分離回収が可能であることが必要であり、その分離回収プロセスも検討する。
    1 本研究では、ZnO、In_2O_3触媒を高温(1000-1300℃)でZn(g),In_2O(g)として石炭灰から気化分離し、直ちに酸化することでZnO、In_2O_3として回収、再利用するプロセスを提案している。小型の反応器を使って、石炭の固定相ガス化の後、ZnO、In_2O_3触媒の高温分離を1150℃においてメタン-CO_2混合ガス気流中で試験した。95〜98%のZn、Inが石炭灰から気化分離された。反応器出口に設置した冷却トラップには、それぞれZnO,In_2O_3粒子が析出し、Zn(g),In_2O(g)を通して触媒が高効率で分離できることが見出された。
    2 鉄酸化物触媒(Fe_2O_3あるいはFe_3O_4)は安価で環境に無害であり、ガス化後の鉄を含んだ石炭灰は、製鉄プラントの高炉に導入して容易に鉄を製鉄として回収できる。そこで赤外線照射小型流動層ガス化装置により触媒活性を試験した。その結果、含有率10wt%、800-900℃でガス化速度を1.5〜2倍に向上させる活性のあることが見出された。
    3 小型の石炭流動層反応器を使って3KWキセノンランプ模擬太陽光の直接照射により、ZnO、In_2O_3、Fe_3O_4触媒の石炭ガス化活性を試験した。照射光エネルギー密度は最大で480kWm^<-2>までしか上げることができなかったが、太陽光/化学エネルギー転換率がIn_2O_3触媒(8wt%)により3倍(6%)に向上できることが見出された。

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  • 天然ガス/未利用熱ハイブリッド型の熱/化学エネルギー転換熱化学サイクルの開発

    研究課題/領域番号:10558072

    1998年 - 2000年

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    児玉 竜也, 藤井 芳夫, 北山 淑江

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    配分額:6800000円 ( 直接経費:6800000円 )

    本研究は、1000℃以下で集光太陽熱等の未利用熱を化学エネルギーへ高効率転換することを目的とし、天然ガス(メタン)を、エネルギー的に高位の燃料に転換する吸熱型の熱化学サイクル反応の検討を行うものである。具体的には、金属酸化物(反応性セラミック)を媒体とする下記の2つの熱化学サイクルで高活性・高選択性を示す反応性セラミックの開発を行う。研究成果は以下の通りである。
    1. メタン改質/水分解サイクル
    CH_4+M_xO_y→M_xO_<y-m-n-1>+(1-N)CO+nCO_2+(2-m)H_2O(1段目:高温吸熱反応)
    M_xO_<y-m-n-1>+(m+n+1)H_2O→M_xO_y+(m+n+1)H_2 (2段目:低温発熱反応)
    高活性セラミックとしてWO_3/ZrO_2とNi_<0.39>Fe_<2.61>O_4/ZrO_2の開発した。特にNi_<0.39>Fe_<2.61>O_4/ZrO_2では900℃以下で良好なサイクル反応を行うことができ、メタン転換率は40〜60パーセントであった。生成合成ガスはほぼメタノール合成に適したH_2/CO比=2を持っており、サンベルト地帯から太陽エネルギーをメタノールにして日本に輸送するという、NEDOで推進中の研究開発事業に適用できると考えられる。2段目の水分解反応で、ほぼ純粋の水素を得ることができ、燃料電池で燃料として容易に利用できる。
    2. メタンカップリング/水分解サイクル
    2CH_4+M_xO_y→M_xO_<y-2>+C_2H_4+2H_2O (1段目:高温吸熱反応)
    M_xO_<y-2>+2H_2O→M_xO_y+2H_2 (2段目:低温発熱反応)
    高活性セラミックとしてSnO_2/Fe_3O_4/SiO_2を開発した。さらに上記の2段階法を、酸化物にメタン/水蒸気混合ガスを同時に流通することによって900℃でサイクルさせ、1段階プロセス化することに成功した。C_2収率は4〜6%であったが、C_2選択率87〜94%を得ることができ、C_2生成速度としては、従来のメタンの水蒸気酸化によるC_2生成触媒と比較して最高速度が得られた。

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  • 粘土層間チタニア架橋体の合成と光触媒への応用

    研究課題/領域番号:10650821

    1998年 - 2000年

    制度名:科学研究費助成事業

    研究種目:基盤研究(C)

    提供機関:日本学術振興会

    北山 淑江, 児玉 竜也

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    配分額:2900000円 ( 直接経費:2900000円 )

    1)粘土層間チタニア架橋体の合成:粘土としてサポナイトを用いたTiO_2-架橋サポナイトの合成はすでに成功した。平成12年度は粘土としてマイカとモンモリロナイトを用いて、TiO_2-架橋粘土の合成を行った。TiO_2-架橋サポナイトの合成と同様に、酢酸溶液中で多核錯体化したTi^<4+>を粘土層間にインターカレートしたものを合成し、これを大気中で焼成することにより有機物を除去した。キャラクタリゼーションは、XRD、表面積、細孔分布、XPS、UV-Vスペクトルなどの測定により行った。マイカ、モンモリロナイトともに架橋体が生成した。比表面積はTiO_2-架橋サポナイトで2.5倍、TiO_2-架橋モンモリロナイトでは50倍、TiO_2-架橋マイカでは100倍に達した。細孔分布曲線の極大値はいずれも直径4.2nmにあり、粘土による差は見られなかった。これより、TiO_2-柱の間隔は粘土による差が現れないものと推察される。
    2)粘土層間ジルコニアおよびチタニア・ジルコニア混合酸化物架橋体の合成:化学的に不安定なジルコニウムアルコキシドを原料として粘土層間チタニア架橋体と同じ方法で合成に成功した。また混合酸化物架橋体では、、柱の組成は、原料となるアルコキシドのTiとZrのモル比に依存することがわかった。
    3)粘土層間チタニア架橋体の光触媒作用:粘土層間チタニア架橋体を触媒としてアルキルアルコールの光分解反応およびベンゼンの部分酸化反応について検討した。アルコールの分解においてはアルキル基の大きさの効果が顕著にあらわれた。ベンゼンの部分酸化反応ではTiO_2触媒単独では、完全酸化がおこりCO_2が多量生成するのに対して、粘土層間チタニア架橋体触媒では、部分酸化物の収量が増加し、CO_2の発生が抑制された。これは、粘土による光の遮蔽効果と細孔の反応場の有効性によるものと考えられる。

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  • 熱/化学エネルギー低温転換を目指した石炭利用型水分解熱化学サイクルの開発

    研究課題/領域番号:09780455

    1997年 - 1998年

    制度名:科学研究費助成事業

    研究種目:奨励研究(A)

    提供機関:日本学術振興会

    児玉 竜也

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    配分額:2000000円 ( 直接経費:2000000円 )

    本研究は、外熱式石炭ガス化反応による集光太陽熱/化学エネルギー転換を行うことを目的として、反応性セラミックを媒体とした以下の2段階熱化学サイクルを検討するものである。
    CH_n(coal)+metal oxide→CO+n/2H_2+metal (1段目)
    metal+H_2O or CO_2→H_2 or CO+metal oxide (2段目)
    上式にあるように2段目の反応では水蒸気の他、二酸化炭素を反応させて一酸化炭素を得ることも可能である。この場合、全反応は石炭のCO_2ガス化反応[CH_n+CO_2→2CO+n/2H_2]となり、水蒸気の場合と同様、太陽熱/化学エネルギー転換ができる。本年度はこちらのサイクルも検討課題に加えた。反応試験は固定床方式、900℃以下で行った。反応性セラミックとして鉄酸化物(フェライト)系を検討した結果、In-フェライトが最も活性が高く、触媒を用いない場合の約3倍の速度で石炭の水蒸気あるいはCO_2ガス化が行えることが見出された。石炭灰からのフェライトの分離回収は磁気分離が考えられる。しかし、磁気分離速度を考慮すると、このプロセスが律速となり全体的な石炭ガス化効率を低下させると予想される。そこで、セラミックを高温(1000℃程度)で気化し、石炭灰から分離回収するプロセスを考案した。既にフェライト系以外ではIn_2O_3がIn-フェライトと同等の高活性を有することを見出しているが、これを分離回収時に高温・還元雰囲気でIn_2O(g)とすれば高速で反応性セラミックを石炭灰から回収できる可能性がある。反応後の石炭灰+In_2O_3を1000℃でCH_4/CO_2(P_<CH4>=50%)混合ガスで処理した結果、石炭灰から82%のInを気化して分離することができた。今後はさらなる回収効率の向上、流動床方式による反応試験、反応システムと分離回収システムの結合を検討していく必要がある。

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  • 無機層状化合物のイオン交換

    1997年

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    資金種別:競争的資金

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  • Study on solar thermochemical water splitting cycle for H<sub>2</sub> production

    1997年

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    資金種別:競争的資金

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  • Study on solar thermochemical, natural-gas reforming and coal gasification to produce hydrogen

    1997年

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    資金種別:競争的資金

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  • Ion Exchange by novel inorganic materials

    1997年

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    資金種別:競争的資金

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  • 水分解熱化学サイクルの研究

    1997年

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    資金種別:競争的資金

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  • 太陽熱による天然ガス改質・石炭ガス化水素製造システムの研究

    1997年

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    資金種別:競争的資金

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  • 平均構造を有するリチウム伝導体

    研究課題/領域番号:08455405

    1996年 - 1997年

    制度名:科学研究費助成事業

    研究種目:基盤研究(B)

    提供機関:日本学術振興会

    佐藤 峰夫, 児玉 竜也

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    配分額:500000円 ( 直接経費:500000円 )

    平均構造を有するリチウムイオン伝導体Li_3M_2(PO_4)_3(M=ScおよびIn)の高温相の超イオン伝導相の室温での安定化と超イオン伝導相の発現に有効な構造に関する基本的な知見を得ることを目的として研究を行った。各々のイオン伝導体は、固相反応により合成した。熱分析は、0.05を超えるxのLi_<3+2X>(Sc_<1-X>Mg_X)_2(PO_4)_3、Li_<3-2X>(Sc_<1-X>A_X)_2(PO_4)_3(A=Ti,Zr,Sn,Hf)および0.025を超えるxのLi_<3-4X>(Sc_<1-X>A_X)_2(PO_4)_3(A=Nb,Ta)において相転移が存在しないことを示していた。TiおよびZr置換において観察された最も高い伝導度は、Li_3Sc_2(PO_4)_3の室温のイオン伝導度より三桁増大している。粉末中性子回折パターンのRietveld解析により決定した結晶構造より、Li_3Sc_2(PO_4)_3の高温相と安定化された化合物が同一の構造を持っていることが確認された。また、リチウムイオンが結晶格子中において統計的に分布し、それにより高温相の安定化が起きていることが明らかになった。これは、超イオン伝導相の発現機構の解明に寄与する重要な知見である。これらの安定化された化合物は化学的に非常に安定であり、全固体型リチウム二次電池用の固体電解質やセンサー材料等への応用が期待される。
    また上述の知見より、Li_3M_2(PO_4)_3(M=ScおよびIn)と同じ構造を持つリチウムバナジウムリン酸塩Li_3V_2(PO_4)_3の高温相の安定化を試みた。10%のZrの置換によりLi_3M_2(PO_4)_3(M=ScおよびIn)と同様な高温相の安定化が起きることが確認された。この化合物をリチウム二次電池の正極材料として用いた場合に、リチウムの拡散性の向上による充放電容量(約1.2倍)の顕著な改善が見られた。すなわち、異種カチオンによる高温相の安定化が、これらの系において共通に用いられることができる有効な手法であることを確認した。

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  • 反応性セラミック利用型水素製造熱化学サイクルを目指した新材料フェライトの開発

    研究課題/領域番号:08780470

    1996年

    制度名:科学研究費助成事業

    研究種目:奨励研究(A)

    提供機関:日本学術振興会

    児玉 竜也

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    配分額:1100000円 ( 直接経費:1100000円 )

    1200℃以下で下記の水分解熱化学サイクルを構築することを目的として、反応媒体となる反応性セラミック新材料の開発を、複合鉄酸化物(フェライト)のredox系で検討した。
    MFe_2O_4→MFe_2O_<4-x>+x/2O_2(酸素放出反応)
    MFe_2O_<4-x>+xH_2O→xH_2+MFe_2O_4(水分解反応)
    Zn(III)-、Mn(II)-フェライトに加え、マグネタイト(Fe_3O_4)、Ni(II)-、Mg(II)-、Co(II)-、In(II)-フェライトの反応性を調べた。比表面積を大きくし、反応を有利にするために粒径20-50nmの超微粒子を合成し、赤外線イメージ炉で作製した太陽炉モデルの反応炉で実験を行った。酸素放出反応に対する反応性を700℃の低温で速度論的に解析するため、炭素(活性炭)を還元剤として加えた。その結果、M=Zn<Mn<Fe<Co<Mg<In<Niの順で格子酸素の放出速度が増大することがわかった。さらにMg(II)以下のフェライトでは準安定ウスタイトで還元が止まるに対し、In(III)、Ni(II)ではα-Fe+In、Ni-Fe合金の金属相まで還元が進行することが見出された。Ni(II)-フェライトについてはNiとの合金化で金属鉄の生成自由エネルギーが低下することが原因と考えられるが、金属Inが独自に形成されるIn(III)-フェライトでは、Fe(II)への電子の授与にInが触媒的に関与するという興味深い還元機構が推察される。これら金属相は500℃で水蒸気を分解して水素を生成し、ほぼ完全にフェライト相に再酸化されることが確認された。次に、In(III)-、Ni(II)-フェライトで活性炭を用いず900℃以下においてN_2気流中での酸素放出反応を試みた結果、金属相の生成はほとんど起らなかった。これらフェライトにさらに改良を加える必要があるが、本研究で見出されたNi(II)-フェライトの低温のおけるNi-Fe合金への転移を、さらにInの触媒効果を利用し低温化することが期待でき、現在、Ni(II)-In(III)-フェライトによって検討中である。

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