Mechanistic Insights into Doping Effects on CH ₄ Combustion over Co ₂ CrO ₄ Spinel Catalysts: A Theoretical Study

The spinel Co-based catalysts have been extensively investigated for catalytic methane combustion. However, it remains a significant challenge to both achieve highly synergistic oxidation activity and elucidate the reaction mechanisms for commonly used doping of secondary metal cations in spinel oxide catalysts. Herein, density functional theory (DFT) fully elucidated the Cr promotion effect in spinel Co2CrO4(110) for CH4 oxidation, involving sequential methane dehydrogenation, O2 dissociation, and H2O formation. The magnetic ordering configurations significantly affect the catalytic activity and reaction mechanisms. The Cr–Cr–Co sites of the Co2CrO4(110) surface with antiferromagnetic structures substantially lower the activation barrier of the initial C–H bond in CH4 and boost O2 dissociation to O*. CH4 complete oxidation proceeds through a synergistic Eley–Rideal (ER) and Langmuir–Hinshelwood (L–H) mechanism, CH4 → CH3O* → OLCH2O* → OLCHO* → O*CO* → CO2(g), rather than the Mars–van Krevelen (MvK) mechanism. Moreover, the coordination environment of surface Cr3+ or Co3+ ions modified by the neighboring preadsorbed O* species can increase the energy barriers for O2 activation, which becomes the rate-determining step (RDS) for the overall reaction. These findings provide theoretical guidance for the rational design of efficient transition metal oxide catalysts based on spin-catalytic synergy.