For the chemical-looping combustion (CLC), readily available metal oxides (NiO, Fe 2 O 3 ) for oxygen carriers and bentonite, TiO 2 , and Al 2 O 3 for the supports of the looping materials were selected. The reactivity of the oxygen carrier particles was determined in a thermobalance reactor under the reducing (CH 4 ) and oxidizing (O 2 ) conditions at 923-1223 K. The reactivity of NiO is higher than Fe 2 O 3 , and the particles supported on bentonite or Al 2 O 3 produce higher reactivity than those on TiO 2 . The reactivity of the metal oxide particles increases with increasing temperature and the amount of NiO. The obtained kinetic data of the NiO-Fe 2 O 3 / bentonite can be analyzed based on the modified volumetric and shrinking core models for the reduction and oxidation conditions, respectively. The CLC experiment was carried out in an annular shape circulating fluidized bed (CFB) reactor with double loops. To determine the optimum fuel gas velocity, the mixture of NiO and Fe 2 O 3 (75:25) on a bentonite support was tested at 1123 K. The CH 4 conversion was higher at lower velocities than that at higher ones, and the optimum CH 4 gas velocity for complete combustion was found to be around 2-3 u mf (minimum fluidizing velocity). Combustion efficiency increases with increasing temperature, and the optimum reaction temperature was found to be around 1123 K. It was found that CO emission from the fuel reactor was negligibly small, and no H 2 emission was detected at the optimum conditions. From the oxidation reactor, NO x emission was also negligibly small, and CO 2 emission was not detected.

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The chemical-looping hydrogen generation (CLH) system consists of reduction of metal oxide and water decomposition by oxidizing reduced metal oxide. In the present study, water decomposition by the reduction and oxidation of metal oxide (CuO) was conducted in a thermogravimetric analysis (TGA) system for the CLH process. The particles are reduced completely in an atmosphere of synthesis gas (H2 + CO), and the fully reduced particles decompose water to produce 3.7 L of H2 per kilogram of metal oxide. The particles prepared by the impregnation exhibits better reactivity than those by coprecipitation and the solid phase method, and the particles supported on Al2O3 exhibit better reactivity than those on SiO2. Based on the TGA, the reduction and oxidation of CuO/Al2O3 prepared via impregnation are characterized by the kinetic equations from the solid-state reaction rate models. The phase-controlled-boundary model was successfully applied to predict the initial stages of reduction and oxidation of the metal oxide, and the activation energies for reduction and oxidation are determined to be 4.13−19.5 and −55.8 kJ/mol, respectively.

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