Investigation of the active centers and structural modifications for TS-1 in catalyzing the Beckmann rearrangement

The Beckmann rearrangement (BR) of cyclohexanone oxime (CHO) to produce caprolactam (CPL) has been studied over various titanosilicates. TS-1 showed superior catalytic performance, compared to Ti-MWW, Ti-Beta and Ti-MOR. Based on the close relationship between Ti content and CHO conversion, and the Na⁺-exchange experiments, the silanol groups, adjacent to the “open” Ti sites, were proved to be the active centers for the BR reaction of CHO to produce CPL, in addition to those generated by defects including terminal silanols, hydrogen-bonded silanols and silanol nests. Moreover, monolithic TS-1 (M-TS-1) microspheres showed higher catalytic activity than the conventional TS-1. The diffusion properties of M-TS-1 were further enhanced via the chemical modifications to achieve longer lifetime for the Beckmann rearrangement under optimized reaction conditions.