Mechanistic studies through H-D exchange reactions: Propane aromatization in HZSM5 and Ga/HZSM5 catalysts

HZSM5 and Ga/HZSM5 catalysts were studied in propane H-D isotopic exchange at various temperatures and D-2 gas partial pressures. Stepwise and multiple exchange were observed on both the pure zeolite and the Ga/FIZSM5 catalyst. Initial product distribution simulations by a Monte Carlo algorithm showed that three processes were necessary to explain the observed patterns in all catalysts: one stepwise and two multiple exchange processes, where one of the multiple exchange processes was observed only on Gal HZSM5. Almost all processes were negatively influenced by D2 partial pressure, indicating competition with propane for the active sites. Reaction mechanisms and intermediate species were proposed for all processes discussed. In the simultaneous H-D exchange and aromatization/hydrogenolysis reactions, it was observed that aromatics were produced after several dehydrogenation-oligomerization-cracking cycles, while methane and ethane were formed mainly by direct propane hydrogenolysis on the Ga+/GaH2+ pair. (C) 2016 Elsevier Inc. All rights reserved.