title: Following solid-acid-catalyzed reactions by MAS NMR spectroscopy in liquid phase--zeolite-catalyzed conversion of cyclohexanol in water.
abstract: A microautoclave magic angle spinning NMR rotor is developed enabling in situ monitoring of solid-liquid-gas reactions at high temperatures and pressures. It is used in a kinetic and mechanistic study of the reactions of cyclohexanol on zeolite HBEA in 130 °C water. The (13) C spectra show that dehydration of 1-(13) C-cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the (13) C label. A simplified kinetic model shows the E1-type elimination fully accounts for the initial rates of 1-(13) C-cyclohexanol disappearance and the appearance of the differently labeled products, thus suggesting that the cyclohexyl cation undergoes a 1,2-hydride shift competitive with rehydration and deprotonation. Concurrent with the dehydration, trace amounts of dicyclohexyl ether are observed, and in approaching equilibrium, a secondary product, cyclohexyl-1-cyclohexene is formed. Compared to phosphoric acid, HBEA is shown to be a more active catalyst exhibiting a dehydration rate that is 100-fold faster per proton.
authors.affiliation: Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352 (USA).
authors.forename: Aleksei
authors.initials: A
authors.lastname: Vjunov
authors.forename: Mary Y
authors.initials: MY
authors.lastname: Hu
authors.forename: Ju
authors.initials: J
authors.lastname: Feng
authors.forename: Donald M
authors.initials: DM
authors.lastname: Camaioni
authors.forename: Donghai
authors.initials: D
authors.lastname: Mei
authors.forename: Jian Z
authors.initials: JZ
authors.lastname: Hu
authors.forename: Chen
authors.initials: C
authors.lastname: Zhao
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Lercher
keywords: NMR spectroscopy; alcohol dehydration; heterogeneous catalysis; reaction mechanisms; zeolites