Non-Oxidative Propane Dehydrogenation by a Well-Defined Ga Catalyst Prepared by Surface Organometallic Chemistry

Ga ions dispersed on alumina catalyze propane dehydrogenation (PDH). Their reactivity has been attributed to the presence of isolated Ga sites, while aggregation to GaOx oligomers and reduction to GaI are reported to be responsible for catalyst deactivation. In this study, we present the preparation and characterization of a highly active and stable single-site catalyst for propane dehydrogenation, consisting of fully dispersed GaIII ions on γ-alumina. The catalyst was synthesized using a surface organometallic chemistry route. Grafting [Ga(OtBu)3]2 onto Al2O3–500 results in the formation of monopodal [(AlsO)Ga(OtBu)2] (I). The controlled thermal treatment of (I) at 300 °C removes the alkoxide ligands and converts (I) into tetracoordinated [(AlsO)3Ga(AlsO-X), X = Als or H] (II). The structures of the intermediate species (I) and the active species (II) were confirmed through elemental analysis, diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), solid-state NMR, and X-ray absorption spectroscopy (XAS). Material (II) was tested in PDH at 540 °C and exhibited high activity and stability compared to its silica-supported counterpart [(≡SiO)3Ga], suggesting that the isolated nature and robust attachment of (II) onto γ-alumina limit its deactivation.