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 (CexZr1−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 1173 K. 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, Ce0.8Zr0.2O2 showed the best stability and gas yields during repeated operations of the redox cycle at 1173 K, and it was confirmed from the XRD analysis that sintering of Ce0.8Zr0.2O2 was the least. To find the effect of metallic foams on the gas productivity, a Ni foam coated with Ce0.8Zr0.2O2 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.