Improving the stability and reactivity of SAPO-11 catalyst for gas-phase beckmann rearrangement by a simple and effective alkali-treated approach

Abstract

ε-Caprolactam (CPL) is an important organic chemical raw material for preparing nylon-6 fiber and polyamide engineering plastics. Traditional production technology based on concentrated sulfuric acid leads to serious environmental pollution. Herein, we develop an economical and environmentally friendly strategy based on SAPO-11 molecular sieve as catalyst to produce CPL. Importantly, alkali engineering strategy to treat SAPO-11 molecular sieve was profited to remove the framework P and increase much Si island edge structures, consequently formatting the larger mesopores and enhancing the acidic properties, thus the catalytic performance and stability of the catalyst were significantly improved. Compared with the original SAPO-11, SAPO-11-TH had outstanding catalytic performance, the conversion of CHO and the selectivity for CPL were still more than 92% and 87% respectively when the reaction continuous reacted for 5 h at 6 h−1 weight hourly space velocity (WHSV). Interestingly, we found that the reactants can complete the conversion within an extremely short residence time (0.86 s), thereby obtaining higher spatiotemporal yields. What else, the catalyst obtained from simple calcination still exhibited excellent catalytic performance. We provide a facile, intriguing and scalable approach to treat catalyst SAPO-11 molecular sieve to form larger mesopores and high acidic strength that can be applied in the many catalytic fields.