Abstract
<jats:p>The selective hydrogenation of CO to oxygenates over unpromoted Mo carbide-based catalysts under Fischer-Tropsch (FT) conditions remains challenging due to the dominance of competing hydrocarbon-forming pathways. Here, we show that SiO2-supported two-dimensional (2D) MXenes Mo2CTx and Mo4/3CTx (Tx = O, OH, F) yield oxygenates under FT conditions, i.e., methanol and dimethyl ether (DME), with ca. 15%–25% selectivity. In contrast, unsupported Mo2CTx and Mo4/3CTx yield mostly kerosene-range alkanes (C5+) and methane, respectively, with only small or no quantities of methanol or DME under comparable conditions. This selectivity difference correlates with distinct reducibility profiles: e.g., while Mo2CTx can be fully reductively defunctionalized via H2 treatment, a similar treatment of Mo2CTx/SiO2 retains a stable Tx coverage of approximately 0.3 monolayer. Density functional theory calculations reveal that on the unsupported Mo2COx model, the progressive removal of O* leads to in-plane lattice expansion, lowering the Mo d-band center and weakening Mo–O* bonds, thereby facilitating the complete defunctionalization by H2. In contrast, a Mo2COx/SiO2 model with a partially defunctionalized MXene exhibits an interfacial MXene–support interaction that constrains lattice expansion and induces a redistribution of the electron density at the reactant-exposed surface. Together, these two effects stabilize residual O* groups on Mo2COx/SiO2, which, in turn, destabilize intermediates of the FT pathway and hinder the diffusion of CHx * species through repulsive O*-CHx * interactions, thereby suppressing C–C coupling and favoring pathways to methanol, DME, and methane. Overall, interfacial polarization, hindered defunctionalization, and surface diffusion are at the origin of the SiO2 support effect, controlling adsorption energies and reaction barriers in Mo-based MXenes, thereby providing guidelines for tuning the selectivity of Mo carbide-based MXene catalysts.</jats:p>