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 Zr[O.sub.2]-supported Ni(II)-ferrite ([Ni.sub.0.39][Fe.sub.2.61][O.sub.4]/Zr[O.sub.2]) as a working material in the temperature range of 1073-1173 K. The produced CO-rich syngas had the [H.sub.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.sub.0.39][Fe.sub.2.61][O.sub.4]/Zr[O.sub.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.sub.0.39][Fe.sub.2.61][O.sub.4]/Zr[O.sub.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.sub.2] under flux irradiation of 500 kW [m.sup.-2] in the residence time less than 1 s.