Structure modification of molybdenum carbide catalysts upon activation treatments and the effect on hydrodeoxygenation of m-cresol. Experimental and theoretical studies

Molybdenum carbide catalysts are promising for hydrodeoxygenation, but their use is hindered by strong oxygen sensitivity, especially in systems requiring ex situ carburization and low-temperature reactivation. In the present work, the reactivation of passivated molybdenum carbide (Mo 2 C) catalysts was investigated through a combined experimental and theoretical approach to elucidate the transformations occurring under hydrogen, while increasing temperature. Passivation produced an oxycarbide-like surface, requiring subsequent reduction to recover the active Mo 2 C phase. Catalysts reactivated at different temperatures were evaluated in the hydrodeoxygenation of m -cresol, showing that the removal of surface oxygen species directly enhances catalytic activity. Ab initio thermodynamic calculations revealed that oxygen desorption from the Mo-terminated surface begins near 300 °C and proceeds progressively with increasing temperature, while the C-terminated surface remains largely inactive. Optimal reactivation was achieved at approximately 500 °C, where theoretical predictions and experimental results converge, indicating extensive oxygen removal and maximum HDO rates (0.73 mmol cresol min −1 g cat −1 ). Above this temperature, both DFT calculations and TPR experiments suggest the onset of surface degradation through carbon abstraction and methane evolution, leading to irreversible structural damage and loss of active sites. Adsorption studies further demonstrated that m -cresol strongly interacts with clean Mo sites but weakly binds to oxygen-covered surfaces, confirming that surface oxygen hinders the HDO reaction. Overall, this study provides a detailed understanding of the reactivation and degradation of Mo 2 C catalysts, establishing an upper operational limit for regeneration and highlighting the role of surface termination in catalytic performance.