Isothermal reverse water gas shift chemical looping on La0.75Sr0.25Co(1−Y)FeYO3 perovskite-type oxides

Abstract

The RWGS-CL is a two-step process for the conversion of CO2 to CO using a redox cycle of a parent metal oxide. Previously, this process was demonstrated using La0.75Sr0.25CoO3 perovskite, but this material required different oxidation and reduction temperatures. In this study, oxidation and reduction were achieved at the same temperature. La0.75Sr0.25Co(1−Y)FeYO3 (Y=0, 0.5, 0.75 and 1) perovskite-type oxides were synthesized by the Pechini method and were tested by X-ray diffraction (XRD), temperature-programmed reduction (H2-TPR) and oxidation with carbon dioxide (CO2-TPO). Results demonstrated that the LaFeO3 (Y=1) sample showed structure stability when reduced at 550°C, the lowest CO formation onset temperature (450°C) and high selectivity toward CO. Five isothermal RWGS-CL cycles were performed at 550°C on the Y=1 sample. The stability of the crystalline structure throughout the cycles was demonstrated by XRD. CO formation rates increased during the first cycles and stabilized at the third cycle due to the increased accumulated amount of oxygen vacancies (δ) on the perovskite surface, which is consistent with the findings from the density functional theory studies that directly correlate the CO2 binding strength to the amount of oxygen vacancies. The high CO formation rates and the repeatability of the process make RWGS-CL a promising technology for CO2 conversion, if a renewable hydrogen source is available.