title: Enhancing the catalytic activity of hydronium ions through constrained environments.
abstract: The dehydration of alcohols is involved in many organic conversions but has to overcome high free-energy barriers in water. Here we demonstrate that hydronium ions confined in the nanopores of zeolite HBEA catalyse aqueous phase dehydration of cyclohexanol at a rate significantly higher than hydronium ions in water. This rate enhancement is not related to a shift in mechanism; for both cases, the dehydration of cyclohexanol occurs via an E1 mechanism with the cleavage of Cβ-H bond being rate determining. The higher activity of hydronium ions in zeolites is caused by the enhanced association between the hydronium ion and the alcohol, as well as a higher intrinsic rate constant in the constrained environments compared with water. The higher rate constant is caused by a greater entropy of activation rather than a lower enthalpy of activation. These insights should allow us to understand and predict similar processes in confined spaces.
authors.affiliation: Department of Chemistry and Catalysis Research Center, TU München, Lichtenbergstrasse 4, 85748 Garching, Germany.
authors.forename: Yuanshuai
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Pacific Northwest National Laboratory, Institute for Integrated Catalysis, P.O. Box 999, Richland, Washington 99352, USA.
authors.forename: Aleksei
authors.initials: A
authors.lastname: Vjunov
authors.affiliation: Pacific Northwest National Laboratory, Institute for Integrated Catalysis, P.O. Box 999, Richland, Washington 99352, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Shi
authors.affiliation: Department of Chemistry and Catalysis Research Center, TU München, Lichtenbergstrasse 4, 85748 Garching, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Eckstein
authors.affiliation: Pacific Northwest National Laboratory, Institute for Integrated Catalysis, P.O. Box 999, Richland, Washington 99352, USA.
authors.forename: Donald M
authors.identifier: 0000-0002-2213-0960
authors.initials: DM
authors.lastname: Camaioni
authors.affiliation: Pacific Northwest National Laboratory, Institute for Integrated Catalysis, P.O. Box 999, Richland, Washington 99352, USA.
authors.forename: Donghai
authors.initials: D
authors.lastname: Mei
authors.affiliation: Department of Chemistry and Catalysis Research Center, TU München, Lichtenbergstrasse 4, 85748 Garching, Germany.
authors.forename: Eszter
authors.initials: E
authors.lastname: Baráth
authors.affiliation: Department of Chemistry and Catalysis Research Center, TU München, Lichtenbergstrasse 4, 85748 Garching, Germany.|Pacific Northwest National Laboratory, Institute for Integrated Catalysis, P.O. Box 999, Richland, Washington 99352, USA.
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Lercher