Aromatization of propane over Ga-modified ZSM-5 catalysts

H-ZSM-5 was modified with gallium by the ion-exchange method and characterized with XRD, SEM, BET, NH3-TPD, Py-IR, ICP, and XPS techniques. The influences of the Si/Al ratios and the pretreatment conditions of the Ga-modified ZSM-5 ((Ga-H)-ZSM-5) on their acidity, gallium species state, and aromatization performance of propane were investigated. It was found that the Si/Al ratio had significant effects on the catalyst acidity and the interaction of non-framework Ga species with zeolite, and hence, the catalytic activity and selectivity for propane aromatization. At 550°C and WHSV of 1.0 h−1, (Ga, H)-ZSM-5 with a Si/Al molar ratio of 30 showed the highest catalytic activity. It was shown that Ga species improved the aromatics selectivity and inhibited cracking reactions. After being reduced in hydrogen, Ga2O3 was most likely transformed into Ga+ and GaH2+ species, and migrated into the zeolite channels. Subsequent air-oxidation treatment of the reduced (Ga, H)-ZSM-5 led to formation of GaO+ species, thus greatly increasing the aromatization activity.