The effect of pre-coking and regeneration on the activity and stability of Zn/ZSM-5 in aromatization of 2-methyl-2-butene

A new method to modify the acidity of zeolite was attempted to improve the activity and stability of Zn/ZSM-5 in aromatization of 2-methyl-2-butene. Pre-coking and regeneration in the presence of O2 at 773 K generated a large exothermic heat in a short time, which resulted in the thermal dealumination of framework aluminum that acted as a Brønsted acid site. The treatment had a profound effect on the acid properties of the catalyst as probed by 27Al MAS NMR, temperature-programmed desorption of ammonia, and pyridine FTIR. The results showed that the concentration of oxygen in regeneration step had critical effects on the acidity and stability of Zn/ZSM-5. Thus improvement of lifetime of Zn/ZSM-5 in aromatization of 2-methyl-2-butene was achieved without deteriorating activity and selectivity by the pre-coking and controlled regeneration by oxygen.