Lewis-Bronsted Acid Pairs in Ga/H-ZSM-5 To Catalyze Dehydrogenation of Light Alkanes

The active sites for propane dehydrogenation in Ga/H-WZSM-5 with moderate concentrations of tetrahedral aluminum in the lattice were identified to be Lewis-Bronsted acid pairs. With increasing availability, Ga+ and Bronsted acid site concentrations changed inversely, as protons of Bronsted 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-Bronsted 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 H-2 and desorption of propene.