Catalytically active sites for the Beckmann rearrangement of cyclohexanoneoxime to epsilon-caprolactam

The rearrangement of cyclohexanone oxime to epsilon-caprolactam was investi gated over heterogeneous catalysts, especially over highly siliceous zeolit es with a MFI structure. The aim of this work was to determine the active s ites on these catalysts, rather than to optimize their catalytic performanc e. Amorphous silica and the silicalite-1 zeolite were chemically modified w ith aqueous acidic or basic solutions. Silicalite-1 was also treated hydrot hermally at temperatures above 400 degrees C. Catalytic reactions were carr ied out with the initial materials and their modifications in a fixed-bed r eactor. Characterization of the catalyst with FT-IR, nitrogen sorption, and XRD revealed significant differences and gave important information about the active sites in the reaction. Silanol nests on the external surface of the highly siliceous ZSM-5 zeolite were most suitable for the Beckmann rear rangement. (C) 1999 Academic Press.