Conversion of Methanol to Aromatic-Rich Gasoline over High-Efficiency Bifunctional Catalysts: Green Synthesis of GaZSM-5 Zeolites via Dry-Gel Conversion Strategy

Abstract

Nanoscale ZSM-5 (AlZ5-D) and Ga-substituted ZSM-5 zeolites ((Al,Ga)Z5-D and GaZ5-D) were synthesized by a green dry-gel conversion strategy. For comparison, ZSM-5 zeolite (AlZ5-T) was also prepared by traditional hydrothermal method. The effects of synthesis method and Ga introduction on the physicochemical property and catalytic behavior of methanol to gasoline (MTG) were studied in detail. The results show that the aromatics selectivity decreased while $$\rm{C}_5^+$$ alkanes selectivity increased for AlZ5-D sample compared with that of AlZ5-T, which was attributed to the significantly reduced density of Bronsted acid sites and weakened strong acidity. After Ga introduction, the acid strength of samples further weakened due to the formation of Si—OH—Ga bridge hydroxyl group by insertion of Ga into the zeolite framework, inhibiting the cracking reaction and thus increasing the gasoline selectivity. Moreover, the extra-framework Ga species, especially in the form of GaO+ in GaZ5-D sample, exhibited high dehydrogenation activity, leading to the highest selectivity of aromatics and gasoline.