Perovskite-Structured Redox Catalysts for Methane Partial Oxidation and Water Splitting in a Hybrid Solar-Redox Process

We report a perovskite promoted iron oxide as a highly effective redox catalyst in a hybrid solar-redox scheme for methane partial oxidation and water-splitting. In contrast to previously reported ferrite materials, which typically exhibit 20% or lower steam to hydrogen conversion, La_0.8Sr_0.2FeO_3-δ (LSF) promoted Fe₃O₄ is capable of converting more than 67% steam with high redox stability. Both experiments and a defect model indicate that the synergistic effect of reduced LSF and metallic iron phases is attributable to the exceptional steam conversion. To further enhance such a synergistic effect, a layered reverse-flow reactor concept is proposed. Using such a concept, over 77% steam to hydrogen conversion is achieved at 930 °C, which is 15% higher than the maximum conversion predicted by second law for unpromoted iron (oxides). When applied to the hybrid solar-redox scheme for liquid fuels and hydrogen co-generation, significant improvements in energy conversion efficiency can be achieved with reduced CO₂ emissions. Aside from LSF promoted iron oxide, effects of A-site and B-site material compositions on the redox performances of perovskite based redox catalysts are also investigated. A non-rare earth metal containing perovskite is found to be highly effective for the proposed hybrid solar-redox process. Over 95% syngas selectivity and 2:1 H₂:CO molar ratio with limited coke formation is found in the methane oxidation step. In addition, over 80% steam to hydrogen conversion is achieved in the water-splitting step. The current study demonstrates that structural and redox properties of perovskite-based redox materials can be optimized for the hybrid solar-redox process.