Modified Beta zeolites as catalysts for the Beckmann rearrangement of cyclohexanone oxime

Aluminum or boron containing Beta zeolites were studied as catalysts for th e Beckmann rearrangement of cyclohexanone oxime to E-caprolactam. Analogous ly to previous investigations on [B]-ZSM-5 zeolites, the selectivity to cap rolactam could be enhanced by simultaneously decreasing reaction temperatur e and pressure to 300 degrees C and 100 mbar, respectively. Postsynthesis m odifications, e.g. calcination, acid treatment, were applied on the initial materials in order to increase the amount of hydroxyl groups on the zeolit es' surfaces, which was proved by FT-LR measurements. Nevertheless, such tr eatments did not lead to better catalytic performances. In the case of the [Al]-Beta zeolite, the maximum selectivity reached up to a value of 91%, wh ereas the [B]-Beta yielded selectivities around 97%. Despite very high init ial conversions, both catalysts showed a significant loss of activity over time-on-stream, which was mostly pronounced using the [B]-Beta. The deactiv ation factor of the latter proved to be fifteen times higher compared to a [B]-ZSM-5 zeolite. Besides investigations of the zeolites' hydroxyls, FT-IR measurements of pyridine adsorption were used in order to obtain informati on on the nature of the catalytic active sites of the catalysts. (C) 1999 E lsevier Science B.V. All rights reserved.