Reaction Between Ethylene and Acetate Species on Clean and Oxygen-Covered Pd(100): Implications for the Vinyl Acetate Monomer Formation Pathway |
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Authors: | Florencia Calaza Zhenjun Li Wilfred T Tysoe |
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Affiliation: | (1) Laboratory for Surface Studies, Department of Chemistry and Biochemistry, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA; |
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Abstract: | Abstract The reaction between gas-phase ethylene and adsorbed acetate species on Pd(100)-p(2 × 2)-O and Pd(100)-c(2 × 2)-O surfaces
is studied using infrared spectroscopy. It is found that acetate species are removed more rapidly by gas-phase ethylene on
oxygen-covered Pd(100) than on Pd(111). However, in contrast to reaction on Pd(111), where vinyl acetate monomer (VAM) formation
is detected by infrared spectroscopy, only CO is found on oxygen-covered Pd(100) surfaces. In the case of Pd(111), it has
been shown that VAM is stabilized on the crowded, ethylidyne-covered surface. Since ethylidyne species do not form on Pd(100),
any VAM that is formed can thermally decompose. The reaction shows an isotope effect when C2D4 is substituted for C2H4, indicating the hydrogen is involved in the rate-limiting step. Based on the surface chemistry found for VAM on a Au/Pd(111)
alloy, where 30 to 40% ML of gold inhibits VAM decomposition, it is suggested that the VAM formation rate will increase on
(100) alloy surfaces, while it will decrease at higher gold coverages since acetate formation is inhibited. |
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