Lewis-Brønsted Acid Pairs in Ga/H-ZSM-5 to Catalyze Dehydrogenation of Light Alkanes

The active sites for propane dehydrogenation in Ga/H-ZSM-5 with moderate concentrations of tetrahedral aluminum in the lattice were identified to be Lewis-Brønsted acid pairs. With increasing availability, Ga⁺ and Brønsted acid site concentrations changed inversely, as protons of Brønsted acid sites were exchanged with Ga⁺. At a Ga/Al ratio of 1/2, the rate of propane dehydrogenation was 2 orders of magnitude higher than with the parent H-ZSM-5, highlighting the extraordinary activity of the Lewis-Brønsted acid pairs. Density functional theory calculations relate the high activity to a bifunctional mechanism that proceeds via heterolytic activation of the propane C-H bond followed by a monomolecular elimination of H₂ and desorption of propene.