Alkyl elimination from aldehydes on zinc oxide: Relevance to allylic oxidation pathways
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The reactions of acetaldehyde, propionaldehyde, and acrolein on the (0001)-Zn polar surface of zinc oxide were investigated using temperature-programmed desorption and X-ray photoelectron spectroscopy. Oxidation of these aldehydes on the (0001)-Zn surface proceeded via two competing pathways: nucleophilic addition of lattice oxygen at the carbonyl carbon followed by hydride elimination to form the corresponding surface carboxylate species, and nucleophilic attack of lattice oxygen at the carbonyl carbon followed by alkyl elimination to form surface formate species. There was a strong temperature dependence of the selectivity toward these two competing pathways; low temperatures favored alkyl elimination, while high temperatures favored hydride elimination. The decomposition of the higher carboxylates resulted in the formation of both unsaturated carbonyl compounds and carbon oxides. The possible implications of these results for allylic oxidation reactions on metal oxide catalysts are discussed. © 1988.
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