In situ solid-state NMR investigations of the vapor-phase Beckmann rearrangement of 15N-cyclohexanone oxime on MFI-type zeolites and mesoporous SBA-15 materials in the absence and presence of the additive 13C-methanol

• Published in: Journal of catalysis Vol. 257; no. 1; pp. 134 - 141
• Main Authors: Reddy Marthala, V.R., Rabl, Sandra, Huang, Jun, Rezai, Sayed A.S., Thomas, Bejoy, Hunger, Michael
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01.07.2008; Elsevier; Elsevier BV
• Subjects: Beckmann rearrangement; Brønsted acid sites; Catalysis; Catalysts; Chemistry; Colloidal state and disperse state; Cyclohexanone oxime; Dehydration; Exact sciences and technology; General and physical chemistry; H-ZSM-5; Ion-exchange; Methanol; NMR; Nuclear magnetic resonance; Porous materials; SBA-15; Silanol groups; Silicalite-1; Solid-state NMR spectroscopy; Spectrum analysis; Surface physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Zeolites; Zeolites: preparations and properties; ε-Caprolactam; Brønsted acid sites; ε-Caprolactam; H-ZSM-5; Cyclohexanone oxime; Solid-state NMR spectroscopy; Beckmann rearrangement; Silanol groups; SBA-15; Silicalite-1; Methanol; In situ; Alcohol; Oxime; NMR spectrometry; Zeolite; Porous material; Mesoporosity; Molecular sieve; Heterogeneous catalysis; Solid state; Beckmann rearrangement;Cyclohexanone oxime;ε-Caprolactam;Methanol;Silicalite-1;H-ZSM-5;SBA-15;Brønsted acid sites;Silanol groups;Solid-state NMR spectroscopy; Additive; Acids; Vapor phase; Alkanol
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2008.04.014

The stepwise conversion of 15N-cyclohexanone oxime into ε-caprolactam via the vapor-phase Beckmann rearrangement on silicalite-1 ( n Si / n Al = 1700 ), siliceous SBA-15 ( n Si / n Al = 1800 ), H-ZSM-5 ( n Si / n Al = 14 ), and [Al]SBA-15 ( n Si / n Al = 8.7 ) in the absence and presence of 13C-methanol was investigated by solid-state 15N and 13C CP/MAS NMR spectroscopy. The MFI-type zeolites and SBA-15 materials are characterized by different acid strengths and pore diameters. The surface OH concentrations in silicalite-1, SBA-15, H-ZSM-5, and [Al]SBA-15 materials were determined to 0.31, 2.81, 1.12, and 1.29 mmol g −1, respectively. 1H, 29Si, and 15N MAS NMR measurements revealed that the Brønsted acidic OH groups of H-ZSM-5 and [Al]SBA-15 and the large concentration of Q 3 silanol groups (Si(OSi) 3OH) in siliceous SBA-15 led to the formation of O-protonated ε-caprolactam. On loading and heating of 15N-cyclohexanone oxime on H-ZSM-5 in the presence of methanol, water was formed via dehydration of methanol into dimethyl ether. These water molecules promoted the conversion of O-protonated ε-caprolactam species into ε-aminocapric acid. In addition, on both silicalite-1 and H-ZSM-5 catalysts, partial conversion of methanol into hydrocarbons, such as isobutane, was observed. Furthermore, isopropylamine was formed on silicalite-1 by the reaction of isobutane and byproducts of the Beckmann rearrangement, such as hydroxylamine. In contrast, no influence and conversion of methanol were found during the Beckmann rearrangement of 15N-cyclohexanone oxime on the mesoporous SBA-15 and [Al]SBA-15 materials.