Direct Observation of Solvent–Reaction Intermediate Interactions in Heterogeneously Catalyzed Alcohol Coupling
- Eri Muramoto
Eri MuramotoJohn A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United StatesMore by Eri Muramoto
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- Dipna A. Patel
Dipna A. PatelDepartment of Chemistry, Tufts University, Medford, Massachusetts 02155, United StatesMore by Dipna A. Patel
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- Wei Chen
Wei ChenDepartment of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, United StatesCenter for Functional Nanomaterials, Brookhaven National Laboratory, Upton, New York 11973, United StatesMore by Wei Chen
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- Philippe Sautet
Philippe SautetDepartment of Chemical and Biomolecular Engineering, University of California, Los Angeles, California 90095, United StatesDepartment of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United StatesMore by Philippe Sautet
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- E. Charles H. Sykes
E. Charles H. SykesDepartment of Chemistry, Tufts University, Medford, Massachusetts 02155, United StatesMore by E. Charles H. Sykes
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- Robert J. Madix*
Robert J. Madix*Email: [email protected]John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, United StatesMore by Robert J. Madix
Abstract
The relative stability of reactive intermediates and reactants on a surface, which dictates the rate and selectivity of catalytic reactions in both gas and liquid phases, is dependent on numerous factors. One well-established example is secondary interactions, such as van der Waals interactions between the catalyst surface and the pendant group of the intermediate, which can govern reaction selectivity for coupling reactions. Herein, we directly show that interactions between adsorbed reaction intermediates and reactant molecules increase the binding energy and affects the geometrical arrangement of coadsorbed reactant/solvent molecules. Evidence for this effect is demonstrated for the oxidative coupling reaction of methanol on a single crystal gold (Au(110)) surface. The rate-limiting reaction intermediate for methanol self-coupling, methoxy, stabilizes excess adsorbed methanol, which desorbs as a result of beta-hydride decomposition of the adsorbed methoxy. Direct molecular-scale imaging by scanning tunneling microscopy, supplemented by density functional theory, revealed interactive structures formed by methoxy and coadsorbed methanol. Interactions between the methoxy intermediate and coadsorbed methanol stabilizes a hydrogen-bonded network comprising methoxy and methanol by a minimum of 0.13 eV per methanol molecule. Inclusion of such interactions between reaction intermediates and coadsorbed reactants and solvents in kinetic models is important for microkinetic analysis of the rates and selectivities of catalytic reactions in both the gas and liquid phases whenever appreciable coverages of species from the ambient phase exist.
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