Active Sites of a [B]-ZSM-5 Zeolite Catalyst for the Beckmann Rearrangement of Cyclohexanone Oxime to Caprolactam

• Published in: Journal of catalysis Vol. 194; no. 1; pp. 122 - 129
• Main Authors: Heitmann, G.P., Dahlhoff, G., Niederer, J.P.M., Hölderich, W.F.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 15.08.2000; Elsevier
• Subjects: [B]-ZSM-5 zeolite; Catalysis; Catalytic reactions; Chemistry; cyclohexanone oxime; Exact sciences and technology; FT-IR; General and physical chemistry; hydroxyl groups; postsynthesis modification; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; water adsorption; ϵ-caprolactam; cyclohexanone oxime; FT-IR; postsynthesis modification; ϵ-caprolactam; [B]-ZSM-5 zeolite; hydroxyl groups; water adsorption; Catalytic reaction; Active site; Beckmann rearrangement; Oxime; Modified catalyst; Zeolite; Experimental study; Molecular sieve; Calcining; Heterogeneous catalysis; Boron; Hydrothermal treatment; Organic amide; Pretreatment
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.2000.2928

[B]-ZSM-5 is a very active and selective catalyst for the vapor-phase Beckmann rearrangement of cyclohexanone oxime to ϵ-caprolactam with high selectivities of up to 95% at 300°C and 100 mbar at complete initial conversion. The nature of the catalytically active sites on [B]-ZSM-5 was determined by investigating the influence of postsynthesis modifications, e.g., calcination under air, acid/base treatment, and hydrothermal treatment on the selectivity. Using FT-IR various hydroxyl groups and silanol nests on the surface of the [B]-ZSM-5 zeolites were found to be the active sites for the Beckmann rearrangement. Further investigations concerned the negative effect of adsorbed water on [B]-ZSM-5, which led to a decrease of its catalytic activity. This effect was shown to be reversible and could be explained with the hydration of boron oxide species on the surface. Experiments with as-synthesized and already calcined [B]-ZSM-5 showed the influence of the boron oxide species, which enhanced the conversion compared to the material without extraframework boron from 70% to 98%.