Thermodynamic Analysis of Syngas Production via the Solar Thermochemical Cerium Oxide Redox Cycle with Methane-Driven Reduction

The present work considers the convergence of two approaches for syngas production: solar fuels via the cerium oxide (ceria) redox cycle and the partial oxidation of methane. The chemical thermodynamics of the ceria-methane system reveal that coupling the reduction of ceria to the partial oxidation of methane enables isothermal cycling at temperatures as low as 1223 K with the additional production of high-quality syngas during the reduction step. The equilibrium non-stoichiometry of the oxidation step has a substantial impact on the conversion of the oxidizer to fuel, with important implications for cycle efficiency. A model of the process thermodynamics is used to evaluate the efficiency of the cycle and its sensitivity to oxidation non-stoichiometry, temperature, and concentration ratio. Reduction with methane enables significant gains in efficiency over other proposed approaches, with plausible solar-to-fuel efficiencies reaching 40% without any heat recovery.