Vapor phase Beckmann rearrangement of cyclohexanone oxime on Hβ-zeolites treated by ammonia

Hβ was synthesized by a hydrothermal method followed by ion exchange and treated with aqueous solutions of ammonia. The obtained catalysts were characterized by BET surface area measurement, XRD, XPS, TEM, IR, pyridine-TPD and studied in the vapor phase Beckmann rearrangement of cyclohexanone oxime. The results show that in comparison with pure Hβ, the ammonia treatments led to higher BET area, lower SiO2/Al2O3 ratio, more total acid sites, more weak acid sites, especially more weak Brønsted acid sites, and slow deactivation in the Beckmann rearrangement reaction. The results indicate that for the catalysts having the structure of β-zeolite, the suitable acid sites for the Beckmann rearrangement might be the weak Brønsted acid sites.