H2−D2 exchange and migration of Ga in H-ZSM5 and H-MOR zeolites

Abstract

Trimethylgallium (TMGa) was loaded by chemical vapor deposition (CVD) on two different zeolites, H-ZSM5 and H-MOR. The interaction of TMGa on zeolite acid sites and the effect of reduction and oxidation treatments were characterized by ICP, XPS, FT-IR and 71 Ga NMR. The capacity of dissociatively adsorption of H 2 and D 2 and the resultant HD desorption was analysed by H 2 −D 2 exchange reaction. The oxidation and specially the reduction treatment provoke the migration and redistribution thought zeolite crystals. FT-IR results show that TMGa reacts with both silanol and stericaly accessible Brønsted acid sites. 71 Ga NMR spectra show that Ga is presents in two different geometries: octahedral and Ga compensating the negative charged Al from the framework zeolite structure. Hydrogen pretreatment of both zeolites has a positive effect on the distribution of Ga. However, Ga species obtained were less active for H 2 −D 2 exchange than the Ga species obtained after oxidation.