Beyond Equilibrated Structures: Sequential Lattice Oxygen Evolution Shapes Mars–van Krevelen Catalytic Oxidation on β-MnO2(110)

Abstract

Catalytic oxidation on a large number of reducible transition metal oxides can be described by the Mars–van Krevelen (MvK) mechanism, wherein the redox behavior of lattice oxygen (O_lat) plays a central role. As a result, the formation energy (E_vac) of the oxygen vacancy (O_V), typically derived from a stoichiometric or thermodynamically equilibrated surface, is widely used as a descriptor of the catalytic activity. However, this approach overlooks the dynamic evolution of the surface due to the continuous consumption of O_lat during the reaction. In this work, using CO oxidation on β-MnO₂(110) as a probe, we combine density functional theory and kinetic Monte Carlo simulations to demonstrate the importance of sequential consumption and regeneration of O_lat in dictating catalytic performance. We find that E_vac is not static but varies with O_V concentration, altering the equilibrium between O_lat reduction and regeneration. As the accumulation of O_V shifts the reaction mechanism from being reduction-dominated to regeneration-dominated, the steady-state surface composition deviates significantly from the prediction based on the thermodynamic equilibrium model. Only by accounting for the dynamic variation of O_lat can the simulated apparent activation energies and reaction orders be closely reconciled with experimental observations. This work challenges the traditional reliance on the initial E_vac and offers a more accurate portrayal of catalytic oxidation within the MvK mechanism, which provides useful guidance for predicting and optimizing catalytic activity toward real-world applications.