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 Co 2 CrO 4 (110) for CH 4 oxidation, involving sequential methane dehydrogenation, O 2 dissociation, and H 2 O formation. The magnetic ordering configurations significantly affect the catalytic activity and reaction mechanisms. The Cr–Cr–Co sites of the Co 2 CrO 4 (110) surface with antiferromagnetic structures substantially lower the activation barrier of the initial C–H bond in CH 4 and boost O 2 dissociation to O*. CH 4 complete oxidation proceeds through a synergistic Eley–Rideal (ER) and Langmuir–Hinshelwood (L–H) mechanism, CH 4 → CH 3 O* → O L CH 2 O* → O L CHO* → O*CO* → CO 2 (g), rather than the Mars–van Krevelen (MvK) mechanism. Moreover, the coordination environment of surface Cr 3+ or Co 3+ ions modified by the neighboring preadsorbed O* species can increase the energy barriers for O 2 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.