Rational construction of multiple hollow silicalite-1 zeolite with enhanced quasi acidity for robust vapor-phase Beckmann rearrangement

Developing efficient and stable zeolites for vapor-phase Beckmann rearrangement of cyclohexanone oxime is still a great challenge to realize epsilon-caprolactam (CPL) green production. In this work, the hierarchical porous silicalite-1 zeolites with multiple hollow structure (S-1-M) are explored by in-situ desilication-recrystallization post-treatment of spongy highway-like zeolites (S-1-S), which are synthesized through silanization synthesis of conventional bulky silicalite-1 (S-1). Compared to S-1, S-1-M achieves superior catalytic performance, with improving the CPL selectivity from 85.7% to 94.1% and prolonging the catalyst lifetime from 74 to 126 h at a weight hourly space velocity (WHSV) of 6 h(-1). Comprehensive physiochemical studies demonstrate that the highly dispersed intracrystalline cavities within S-1-M endow greater mass diffusion and better quasi acidity inducing by the enhanced H-bonds among abundant H-bonded silanols, which is cooperatively responsible for its superior catalytic performance.