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

Aluminum or boron containing Beta zeolites were studied as catalysts for the Beckmann rearrangement of cyclohexanone oxime to ϵ-caprolactam. Analogously to previous investigations on [B]-ZSM-5 zeolites, the selectivity to caprolactam could be enhanced by simultaneously decreasing reaction temperature and pressure to 300°C and 100 mbar, respectively. Post-synthesis modifications, e.g. calcination, acid treatment, were applied on the initial materials in order to increase the amount of hydroxyl groups on the zeolitesʹ surfaces, which was proved by FT-IR measurements. Nevertheless, such treatments 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%, whereas the [B]-Beta yielded selectivities around 97%. Despite very high initial conversions, both catalysts showed a significant loss of activity over time-on-stream, which was mostly pronounced using the [B]-Beta. The deactivation factor of the latter proved to be fifteen times higher compared to a [B]-ZSM-5 zeolite. Besides investigations of the zeolitesʹ hydroxyls, FT-IR measurements of pyridine adsorption were used in order to obtain information on the nature of the catalytic active sites of the catalysts.