Effect of the Si/Al ratio on the performance of hierarchical ZSM-5 zeolites for methanol aromatization

A series of hierarchical ZSM-5 zeolites with different Si/Al ratios were successfully prepared using a seed-deduced method and the addition of organosilicone reagents into the medial synthesis system. The crystallinity, morphology, chemical composition, acidity and textural property of the ZSM-5 zeolites were characterized using XRD, SEM, TEM, N-2 adsorption, Al-27 MAS NMR and NH3-TPD. The catalytic performance was evaluated in terms of methanol aromatization to investigate the effects of the Si/Al ratio on the catalyst stability and coke formation. The results indicated that despite their large external surface area and mesopore volume, a decrease in the Si/Al ratio resulted in an increase in the acidity of the zeolites, which significantly increased the coke formation and decreased their catalytic stability. The acid amount exhibits good linear correlation with the coke content, and the generalized and quantitative correlations are reported.