Metastable C-Mo-O/Ni sites mediate partial oxidation of methane via O* species-assisted C-H bond activation pathway

The partial oxidation of methane (POM) is hampered by the high kinetic barrier of C-H bond activation, which demands high operating temperatures, and catalyst surface oxidation induces detrimental deactivation. This paper describes that the dual role of molybdenum carbide (MoC_x) enables facile methane activation and imparts oxidation resistance to Ni-based catalysts. We found that MoC_x modifies the reaction mechanism by altering oxygen adsorption, becoming the preferred site for oxygen activation and thereby protecting the Ni surface. In situ spectroscopy, transient and steady-state kinetics, and density functional theory calculations reveal the formation of a metastable C-Mo-O/Ni interface under reaction conditions. This interface provides a mechanism of O*-assisted C-H bond activation pathway instead of direct oxidation or combustion and reforming POM mechanism, lowering its activation energy. Concurrently, MoC_x maintains Ni in electron-deficient metallic state, effectively suppressing its oxidation. It achieves ∼94% CH₄ conversion and 99% syngas selectivity during a 75-h stability test at 720 °C. This work underscores the role of transition metal carbides as functional oxygen regulators, where the formation of oxycarbide intermediates dictates catalytic performance. The philosophy for anti-oxidation stability could generate broader implications for heterogeneous catalyst design.