Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.egypro.2015.03.088

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ijhydene.2014.10.084

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Language：English   Publishing type：Research paper (scientific journal)  

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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Language：English   Publishing type：Research paper (scientific journal)  

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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Language：English   Publishing type：Research paper (scientific journal)  

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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Language：English   Publishing type：Research paper (scientific journal)  

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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Language：English   Publishing type：Research paper (international conference proceedings)  

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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/cr050188a

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (scientific journal)  

DOI： 10.24632/jses.49.4_71

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Publishing type：Research paper (scientific journal)   Publisher：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 > Solar Energy

Emerging Technologies > Energy Storage

Emerging Technologies > Materials

DOI： 10.1002/wene.440

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Other Link： https://onlinelibrary.wiley.com/doi/full-xml/10.1002/wene.440

DOI： 10.57372/00009749

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Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

DOI： 10.1299/jtst.22-00061

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Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (international conference proceedings)  

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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Publishing type：Research paper (international conference proceedings)  

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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Publishing type：Research paper (international conference proceedings)  

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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Publishing type：Research paper (international conference proceedings)  

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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.est.2020.101420

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.renene.2019.07.039

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Publishing type：Research paper (international conference proceedings)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ijheatmasstransfer.2019.03.153

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Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.cej.2018.10.111

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Publishing type：Research paper (scientific journal)   Publisher：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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Publishing type：Research paper (international conference proceedings)   Publisher：AIP Publishing  

DOI： 10.1063/1.5117684

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Publishing type：Research paper (international conference proceedings)  

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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Solar gasification is one of the promising techniques to convert the carbonaceous materials to clean chemical fuels, which offers the advantages of being transportable as well as storable for extended period of time. In this study, thermal performance of a recently developed 5 kW fluidized bed reactor for solar gasification has been investigated and reported. Discrete element method (DEM) has been used for modeling the granular flow, and computational fluid dynamics (CFD) method has been used for modeling the multiphase flow. To validate the developed model, experiments were preformed and compared with modeling results. Discrete ordinate radiation model has been used to solve the radiative transfer equation. The thermal performance of the reactor and particulate flow behavior have been predicted and the effect of particle size, particle size distribution and gas flow rate are analyzed. The results indicate that the performance of the bed increases when fluidizing the annulus region particles as the high porosity increases the diffusion rate of radiation throughout the bed. th

DOI： 10.1016/j.ijhydene.2018.06.033

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.solener.2018.06.006

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.ijheatmasstransfer.2017.09.015

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：AMER INST PHYSICS  

This paper presents a numerical analysis of unconstrained melting of high temperature(>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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The characteristics of oxygen/hydrogen productivity using 30-mol%-M (M = Fe, Co, Ni, Mn)-doped CeO2-delta (30-mol%-M-CeO2-delta) were studied for the thermochemical two-step water splitting cycle comprising TR (thermal reduction) at 1500 degrees C and WD (water decomposition) at 1150 degrees C. The reproducibility of oxygen evolution was evaluated using 30-mol%-M-CeO2-delta and the effects of different M dopants were compared in the TR temperature range of 1200-1500 degrees C. Two solid phases detected in the 30-mol%-M- CeO2-delta powders were involved in the redox reaction of the thermochemical two-step water splitting cycle. Among the M-CeO2-delta samples evaluated, Mn-doped CeO2-delta provided the most stable and reproducible results and the highest reactivity for oxygen evolution at all temperatures employed for the TR step of the thermochemical two-step water-splitting cycle. (C) 2015 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.energy.2015.06.085

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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 (> 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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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/).

DOI： 10.1016/j.egypro.2014.03.204

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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/).

DOI： 10.1016/j.egypro.2014.03.210

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)  

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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Language：Japanese   Publisher：The Japan Institute of Energy  

Double-walled reactor tubes with molten-salt thermal storage were developed for solar air receiver to generate electricity and for solar reforming to produce solar fuel. A mixture of Na_2CO_3 and MgO was loaded as a thermal storage medium into the outer annulus of that. Performances of the reactor tubes were studied as an air receiver and as a reformer tube in the present study.

DOI： 10.20550/jietaikaiyoushi.21.0_232

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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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Language：English   Publishing type：Research paper (international conference proceedings)  

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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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Language：English   Publishing type：Research paper (scientific journal)  

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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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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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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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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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 <= x <= 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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：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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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.

DOI： 10.1021/cm050982c

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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 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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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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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 > Pd-SH-SiO2 > 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(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 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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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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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.

DOI： 10.1039/b312620j

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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+<Mg2+<Sr2+<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 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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/s0360-5442(03)00093-8

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DOI： 10.1021/ef020270y

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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 < Sr < Ba < 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 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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DOI： 10.1021/ef0200525

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DOI： 10.1021/ef010289l

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DOI： 10.1021/ef0200018

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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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.

DOI： 10.1023/A:1009634506284

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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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.

DOI： 10.1021/ef000130t

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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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(+) --> 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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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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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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 --> 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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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+ >> Sr2+ > 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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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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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) --> 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 --> CO + (n/2+1)H-2 and CHn + CO2 --> 2CO + n/2H(2).

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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 --> 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 --> H-2 + metal oxide
CO2 + reduced metal oxide --> CO + metal oxide
The net reactions are 2CH(4) --> C2H(n) + (4-n/2)H-2, and 2CH(4) + (4-n/2)CO2 --> 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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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.

DOI： 10.1039/a806758i

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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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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 --> 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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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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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 >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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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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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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Language：English   Publisher：The Magnetics Society of Japan  

  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) CH₄ + xH₂O → 2C₂H₄ + xCO + (3x+4)H₂. Oxides of Zn, Mn, Co, Ni, Mg, and Fe were used at 900 °C. The greatest activity for C₂H₄ formation was observed with Fe₃O₄ (magnetite). Substitution of Mn(II) for Fe(II) in magnetite slightly increased the activity for C₂H₄ formation. The surface-lattice oxygens of the wustite (FeO) phase formed by the reduction of MFe₂O₄ (M = Fe, Zn, Mn) with CH₄ are believed to be active in the oxidation of CH₄ to C₂H₄. If this oxidative coupling over MnFe₂O₄ is combined with the reverse water gas shift reaction, the highly endothermic reaction 13CH₄ + 9H₂O → 2C₂H₄ + 9CO + 31H₂ is realized below 900°C.

DOI： 10.3379/jmsjmag.22.S1_400

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&nbsp;&nbsp;This paper proposes a new application of ferrites for a thermochemical reduction of CO₂ 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_&tau; &rarr; reduced ferrite + xCO + (1-x)CO₂ + &tau;/2H₂<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)CO₂ &rarr; ferrite + (2-x)CO,<br>where CH_&tau; 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_&tau; + CO₂ &rarr; 2CO + &tau;/2H₂ 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 CO₂ 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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&nbsp;&nbsp;Ultrafine ferrites, represented by x(MFe₂O₄)-y(Fe₃O₄)-z(Fe₂O₃), 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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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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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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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 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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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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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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publisher：The Magnetics Society of Japan  

Ultrafine Ni(II)-bearing ferrites (UNFs) with 14-100% Ni(II)-substitution of <i>x</i> in Ni_<i>x</i>Fe_3-<i>x</i>O₄ for Fe²⁺ in magnetite were synthesized by hydrolysis of Ni²⁺, Fe²⁺, and Fe³⁺ 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>_s)much lower than the theoretical <i>M</i>_s.

DOI： 10.3379/jmsjmag.20.305

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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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Language：English   Publishing type：Research paper (scientific journal)   Publisher：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

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Language：English   Publishing type：Research paper (scientific journal)  

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

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

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Applicant：新潟大学

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