Overcoming equilibrium constraints in the reverse water gas shift with counter-current gas–solid flow and oxygen transport in La0.75Sr0.25Cr0.5Mn0.5O3-δ

Abstract

Utilizing carbon dioxide in the reverse water gas shift (RWGS) reaction (CO2+H2→CO+H2O) is a potential pathway for mitigating CO2 emissions, as the resulting CO can be used to produce valuable products, such as chemicals and fuels. Here, we explore the implementation of the RWGS reaction by solid-oxide redox cycling in a two-reactor moving-bed process with counter-current gas–solid flow. We also develop a method for obtaining design diagrams from the thermodynamic data of the solid oxide utilized for redox cycling. Using this tool and screening the previous literature for relevant thermodynamic data, we identify the perovskite La0.75Sr0.25Mn0.5Cr0.5O3-δ as a highly promising candidate material, and we experimentally determine its non-stoichiometry under conditions relevant for the RWGS. The reaction kinetics are also obtained for its reduction in H2 and its reoxidation in CO2. We observe that the inward diffusion of oxygen into the perovskite grains during reoxidation in CO2 is likely to determine the minimum feasible temperature at which this process can be operated, and we estimate an effective diffusion coefficient of D = 7.7−1.4+1.8 *10−14 cm2 s−1 at T = 550 °C, with an activation energy of 122±4.4 kJ mol−1. Implementing the RWGS with this material in counter-current gas–solid flow is expected to significantly improve the RWGS process by decreasing the operating temperature, enabling continuous gas production, and increasing the gas conversion.