Thermochemical conversion of carbon dioxide by reverse water-gas shift chemical looping using supported perovskite oxides

Abstract

Perovskite-type oxides show clear potential for thermochemical solar-driven CO2 conversion. These materials exhibit the exact characteristics (e.g., structural endurance and high oxygen redox capacity and exchange kinetics) required by the low temperature reverse water-gas shift chemical looping process. In this study, the La0.75Sr0.25FeO3 (LSF) perovskite oxide was combined with various supports, including popular redox materials CeO2 and ZrO2 along with more abundant alternatives such as Al2O3, SiO2, and TiO2, for potential application at industrial scale. Supporting LSF on SiO2 by 25% mass resulted in the largest increase of 150% in CO yields relative to unsupported perovskite after reduction at 600 °C. This is a result of significantly reduced perovskite oxide particle size confirmed by SEM/TEM imaging and crystallite size from Scherrer analyses of XRD patterns. Due to solid-state reactions, minor secondary phases were observed at the LSF:support interface when using SiO2 or TiO2. Oxygen vacancy formation occurred only on the perovskite oxide phase, as suggested by low temperature experiments and consistent with density functional theory calculations. The role of each metal oxide support towards suppressing or enhancing the CO2 conversion is elucidated. Through utilization of SiO2 as support, the reverse water-gas shift chemical looping process using perovskite-based composites was significantly improved.