Oxidation of Styrene and Phenylacetaldehyde on Ag(111):  Evidence for Transformation of Surface Oxametallacycle

The oxidation of phenylacetaldehyde has been used to help identify intermediates involved in the secondary oxidation reactions of styrene. Besides the epoxidation reaction found for styrene, styrene and phenylacetaldehyde undergo the same secondary oxidation reactions on oxygen-covered Ag(111) to produce CO2, H2O, benzoic acid, benzene, phenyl, biphenyl, and a small amount of benzeneacetic acid. In addition to oxametallacycle and benzoate intermediates, a stable combustion intermediate is identified in the oxidation of styrene on Ag(111). The oxametallacycle and the combustion intermediate evolve into styrene oxide or into other secondary oxidation products, respectively. Isotopic labeling and X-ray photoelectron studies show that the transformation of surface oxametallacycle to the combustion intermediate is kinetically important in determining the selectivity of styrene epoxidation.