Reverse Water Gas Shift over CaO under Calcination Conditions: Interplay between H2O Inhibition, CO2 Equilibrium, and Surface Dynamics

Abstract The integration of CO2 capture and utilization is a promising strategy for carbon management. In CaO-based systems, CaO can act as a CO2 sorbent during carbonation and as reverse water–gas shift (RWGS) catalyst during regeneration. However, the interaction between CaCO3 decomposition and catalytic reactivity remains poorly understood. In this work, the RWGS activity of CaO was investigated under conditions relevant to desorption-enhanced reverse water–gas shift (DERWGS). Conventional power-law kinetics were unable to reproduce the experimental results, whereas the inclusion of an H2O inhibition term accurately described the observed behavior and yielded physically meaningful reaction orders. The kinetic analysis identified H2O inhibition as a key factor governing RWGS activity. Combined analysis of RWGS and calcination kinetics reveals that the overall process arises from the coupling between CO2 release during calcination and its catalytic conversion on CaO. Cycling experiments further show that catalyst deactivation follows the decay in CO2 carrying capacity, suggesting a common structural origin. These findings provide a kinetic framework for describing DERWGS as a dynamically evolving system governed by the interplay between solid-state transformation and catalytic surface processes.