Direct synthesis of Zn-incorporated nano-ZSM-5 zeolite by a dry gel conversion method for improving catalytic performance of methanol to aromatics reaction

摘要

A series of Zn-incorporated nano-ZSM-5 zeolites were synthesized by a dry gel conversion (DGC) method using tetrapropylammonium hydroxide (TPAOH) as a single template, and their activity in methanol to aromatics (MTA) process was investigated. The characterization results revealed that the introduction of Zn species slightly decreased the crystal size with the formation of some agglomerated particles. We also demonstrated that new Lewis acid sites formed in Zn-incorporated nano-ZSM-5 zeolite at the expense of Bronsted acid sites. The amount of medium acid sites in Zn-modified samples increased with increasing of Zn contents. Catalytic evaluation results revealed that the selectivity of BTX and aromatics for the sample synthesized via direct synthesis (Zn-NZ5-3) is increased from 24.0% and 37.9% to 27.9% and 46.4%, respectively. In addition, the lifetime of the sample prepared by the direct synthesis (Zn-NZ5-3) was 33% longer than that of the impregnated sample, while the selectivity of BTX and aromatics was slightly higher.