In-Site Boron Doping Microenvironmental Modulation toward Recyclable SAPO-11 for Efficient Beckmann Rearrangement of Cyclohexanone Oxime

In the research of gas-phase Beckmann rearrangement reactions, the employment of modified molecular sieve catalysts has garnered significant research attention. However, the prevalent supported molecular sieve catalysts currently face two formidable challenges. First, the loaded catalytic species are susceptible to detachment, compromising the catalyst's stability over time. Second, there is a pressing need to enhance the catalytic efficiency to cater to the requirements of modern, highly efficient catalytic processes. Employing a unique microenvironmental framework modification technique, this study has successfully synthesized a silicoaluminophosphate molecular sieve in situ boron doping on the AEL structure. The molecular sieve B-SAPO-11 exhibited a high specific surface area (195.71 m²/g) and enlarged micropore volume (0.065 cm³/g), providing abundant reaction sites and enhancing the efficiency of mass transport and diffusion, respectively, thus giving a favorable microenvironment for the reaction. The catalyst B-SAPO-11 showed an excellent catalytic performance in the gas Beckmann rearrangement reaction of cyclohexanone oxime. The reaction achieved a 96.5% conversion rate and 91.6% selectivity of the desired product under a weight hourly space velocity of 6 h^-1 and a temperature of 400 °C. DFT calculations show that adding B forms a synergistic effect with Al, and the dual Bronsted acid catalysis reduces the reaction energy barrier (11.43 kJ/mol). This method has the advantages of high yield of the target product, rapid reaction, and easy catalyst recovery; a new idea was designed to prepare catalysts for gas-phase Beckmann rearrangement reactions.