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.