Cyclic production of syngas and hydrogen through methane-reforming and water-splitting by using ceria-zirconia solid solutions in a solar volumetric receiver-reactor

For cyclic production of syngas and hydrogen by methane reforming (reduction) and water splitting (re-oxidation) under simulated solar-light irradiation, foam devices coated with ceria-zirconia (Ce_xZr_1-xO₂, where x=0.3, 0.5 and 0.8) solid solutions and CeO₂ were used. Reduction characteristics of the foam devices were investigated in the temperature range from 873 to 1173K. The solid solutions were found to be reduced more easily than pure CeO₂ especially at low temperatures. The gas yields by the solid solutions increased with increasing Ce content. Depending on temperature and composition of the solid solutions, the optimum operating times for methane reforming, during which carbon deposition was negligible, were determined. Among the solid solutions, Ce_0.8Zr_0.2O₂ showed the best stability and gas yields during repeated operations of the redox cycle at 1173K, and it was confirmed from the XRD analysis that sintering of Ce_0.8Zr_0.2O₂ was the least. To find the effect of metallic foams on the gas productivity, a Ni foam coated with Ce_0.8Zr_0.2O₂ was investigated, and it rendered significantly higher gas yields than the SiC foam device; however, its long-term stability was assessed to be inferior to the latter.