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

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Abstract 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 ZrO 2 -supported Ni(II)–ferrite (Ni 0.39 Fe 2.61 O 4 /ZrO 2 ) 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 Ni 0.39 Fe 2.61 O 4 /ZrO 2 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 Ni 0.39 Fe 2.61 O 4 /ZrO 2 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.