Metastable gallium hydride mediates propane dehydrogenation on H 2 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 H 2 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 H 2 co-feeding, the dissociative adsorption of H 2 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 H 2 co-feeding, the alumina-supported, trace additive-modified gallium oxide catalyst GaO x -Ir-K/Al 2 O 3 exhibited high activity and selectivity at high propane concentrations.