Metastable gallium hydride mediates propane dehydrogenation on H₂ co-feeding

In heterogeneous catalysis, the catalytic dehydrogenation reactions of hydrocarbons often exhibit a negative pressure dependence on hydrogen due to the competitive chemisorption of hydrocarbons and hydrogen. However, some catalysts show a positive pressure dependence for propane dehydrogenation, an important reaction for propylene production. Here we show that the positive activity dependence on H₂ partial pressure of gallium oxide-based catalysts arises from metastable hydride mediation. Through in situ spectroscopic, kinetic and computational analyses, we demonstrate that under reaction conditions with H₂ co-feeding, the dissociative adsorption of H₂ on a partially reduced gallium oxide surface produces H atoms chemically bonded to coordinatively unsaturated Ga atoms. These metastable gallium hydride species promote C-H bond activation while inhibiting deep dehydrogenation. We found that the surface coverage of gallium hydride determines the catalytic performance. Accordingly, benefiting from proper H₂ co-feeding, the alumina-supported, trace additive-modified gallium oxide catalyst GaO_x-Ir-K/Al₂O₃ exhibited high activity and selectivity at high propane concentrations.