Following Solid‐Acid‐Catalyzed Reactions by MAS NMR Spectroscopy in Liquid Phase—Zeolite‐Catalyzed Conversion of Cyclohexanol in Water |
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Authors: | Aleksei Vjunov Mary Y Hu Dr Ju Feng Dr Donald M Camaioni Dr Donghai Mei Dr Jian Z Hu Dr Chen Zhao Prof Dr Johannes A Lercher |
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Institution: | 1. Institute for Integrated Catalysis, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA 99352 (USA);2. Department of Chemistry and Catalysis Research Institute, TU München, Lichtenbergstrasse 4, 85748 Garching (Germany) |
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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 13C spectra show that dehydration of 1‐13C‐cyclohexanol occurs with significant migration of the hydroxy group in cyclohexanol and the double bond in cyclohexene with respect to the 13C label. A simplified kinetic model shows the E1‐type elimination fully accounts for the initial rates of 1‐13C‐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. |
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Keywords: | alcohol dehydration heterogeneous catalysis NMR spectroscopy reaction mechanisms zeolites |
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