The kinetics of the reaction between gas-phase ethylene and adsorbed acetate species to form vinyl acetate monomer (VAM) on a Pd(111) surface are measured using infrared spectroscopy to monitor the rate of acetate removal, as well as the rates of VAM and ethylidyne formation, at various temperatures. The results are fit using a kinetic model first proposed by Samanos in which ethylene reacts with acetate species to form an acetoxyethyl intermediate that forms VAM via β-hydride elimination. The results of the kinetic model agree well with the experimental data and Arrhenius plots of the rate constants yield activation energies that are in good agreement with those predicted by density functional theory (DFT) calculations. DFT also predicts that the reaction activation energies should depend on the acetate coverage while the experimental data can be fit by constant values of the rate constants, suggesting that the reaction activation energies are similar for a reaction center surrounded either by acetate species, ethylidynes, or a combination of both. Finally, the kinetic parameters for VAM desorption are in good agreement with the experimental peak temperature measured by temperature-programmed desorption for VAM desorbing from an ethylidyne-covered surface.
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Acknowledgements We gratefully acknowledge support of this work by the U.S. Department of Energy, Division of Chemical Sciences, Office of Basic Energy Sciences, under Grant No. DE-FG02-92ER14289.
- Density functional theory
- Reaction kinetics
- Vinyl acetate synthesis