Highly Active and Selective Sites for Propane Dehydrogenation in Zeolite Ga-BEA

Abstract

A highly selective Ga-modified zeolite BEA for propane dehydrogenation has been synthesized by grafting Ga on Zn-BEA followed by removal of Zn in the presence of H₂. A propene selectivity of 82% at 19% propane conversion illustrates the high selectivity at 813 K. The kinetic model of the catalyzed dehydrogenation including the elementary steps of propane adsorption, first and second C-H bond cleavage, and propene and H₂ desorption demonstrates that the propane dehydrogenation rate is determined by the first C-H bond cleavage at low <i>p</i>_C₃H₈, while at high <i>p</i>_C₃H₈, the rate is limited by the desorption of H₂. The active sites have been identified as dehydrated and tetrahedrally coordinated Ga³⁺ in the *BEA lattice. The low selectivity toward aromatics is concluded to be associated with the high Lewis acid strength of lattice Ga³⁺ and the low Brønsted acid strength of the hydrated Ga sites.