Stepwise production of CO-RICH syngas and hydrogen via solar methane reforming by using a Ni(II)-ferrite redox system

The methane reforming process combined with metal-oxide reduction was examined on iron-based oxides of Ni(II)-, Zn(II)-, and Co(II)-ferrites, for the purpose of converting solar high-temperature heat to chemical fuels of CO-rich syngas and reduced metal oxide as storage and transport of solar energy. It was found that the Ni(II)-doping effectively improves the reactivity of magnetite as an oxidant for methane reforming. A two-step cyclic steam reforming of methane, which produces CO-rich syngas and hydrogen uncontaminated with carbon oxides alternately in the separate steps, was successfully demonstrated by using a ZrO2-supported Ni(II)-ferrite (Ni0.39Fe2.61O4/ZrO2) as a working material in the temperature range of 1073-1173 K. The produced CO-rich syngas had the H-2/CO ratio that was more suitable for methanol production than that produced by a conventional single-step steam reforming. This syngas production using the Ni0.39Fe2.61O4/ZrO2 as an oxidant was also demonstrated under direct irradiation by a solar-simulated, high-flux visible light in laboratory-scale fixed bed system. The directly-irradiated Ni0.39Fe2.61O4/ZrO2 particles acted simultaneously as good radiant absorbers and reactive chemical reactants to yield more than 90% of methane conversion to a 2:1 molar mixture of CO and H-2 under flux irradiation of 500 kW m(-2) in the residence time less than 1 s. (C) 2003 Elsevier Science Ltd. All rights reserved.