Effect of Coadsorbed Water on Deep Oxidation Mechanisms: Temperature-Programmed Reactions of Benzene and Hydroxyl on the Pt(111) Surface

The deep oxidation of benzene by preadsorbed hydroxyl on the Pt(111) surface has been characterized using temperature-programmed reaction spectroscopy. A mechanism for benzene oxidation in the presence of coadsorbed water has been developed based on these experiments. Reaction-limited carbon dioxide and water are formed over the temperature range 330–530 K, indicating oxydehydrogenation and skeletal oxidation are occurring over this temperature range. Oxidation of benzene has been compared on the oxygen-covered Pt(111) surface with and without coadsorbed water. With preadsorbed hydroxyl, the yield of water at low-temperatures is increased, and the yield of carbon dioxide is increased. The temperature ranges for carbon dioxide and water formation above 300 K are increased by 30 K when water is coadsorbed with atomic oxygen to form hydroxyl. These results clearly suggest that hydroxyl enhances oxydehydrogenation below 300 K, which results in the formation of different dehydrogenated intermediates with increased activation energy for oxidation during the reaction. Taken together these kinetic and mechanistic results provide a clear description of the reactivity of hydroxyl during benzene deep oxidation on the Pt(111) surface.