Catalyst preparation for vapor phase Beckmann rearrangement via deboronation/desilication of B-ZSM-5

Vapor phase Beckmann rearrangement of cyclohexanone oxime to ε-caprolactam is an outstanding achievement of green chemistry. Nest silanols in the vicinity of the external surface of silicalite-1 has been proposed as active sites. In this study, B-ZSM-5(Si/B ratio = 25) was synthesized and the product was agglomerates of nanocrystals. As-made B-ZSM-5 was calcined in air and deboronated by treatment with HCl aq. at 353 K for 3 h. Further, the deboronated sample was desilicated with a mixture of ammonia nitrate and ammonia to develop effective diffusion pathways in the catalyst particles. FT-IR study confirmed the formation of abundant nest silanols. The vapor phase Backmann reaggrangement was performed in a plug flow reactor with a fixed bed of catalyst at WHSV = 8 h^-1 and 653 K. The initial catalytic activity was greatly improved by the treatment performed in this study: The pseudo-first-order reaction constant for the parent B-ZSM-5 was 1.8×10^-3 s^-1, but that for the deboronated/desilicated ZSM-5 was 0.13 s^-1.