Aromatization over nanosized Ga-containing ZSM-5 zeolites prepared by different methods: Effect of acidity of active Ga species on the catalytic performance

Nanosized Ga-containing ZSM-5 zeolites were prepared via isomorphous substitution and impregnation followed by characterized using various techniques. The catalytic performance of the zeolites for the aromatization of 1-hexene was investigated. The results indicate that isomorphous substitution promotes the incorporation of Ga heteroatoms into the framework along with the formation of extra-framework GaO+ species ([GaO+](a)) that have stronger interactions with the negative potential of the framework. In addition, based on the Py-IR results and catalytic performance, the [GaO+](a) species with stronger Lewis acid sites produced a better synergism with moderate Bronsted acid sites and thus improved the selectivity to aromatic compounds. However, the impregnation results in the formation of Ga2O3 phase and small amounts of GaO+ species that are mainly located on the external surface ([GaO+](b)), which contribute to weaker Lewis acid sites due to weaker interactions with the zeolite framework. During 1-hexene aromatization, the nanosized Ga isomorphously substituted ZSM-5 zeolite samples (Gax-NZ5) exhibited better catalytic performance compared to the impregnated samples, and the highest aromatic yield (i.e., 65.4 wt%) was achieved over the Ga4.2-NZ5 sample, which contained with the highest Ga content. (C) 2017 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.