Temperature-Programmed Desorption Study of Ethylene on a Clean, a H-Covered, and an O-Covered Pt(111) Surface

The reactions of ethylene on a clean, a H-covered, and an O-covered Pt(111) surface were studied by temperature-programmed desorption. On the clean surface, ethylene is first converted to ethylidyne and then is decomposed in steps eventually into a surface carbonaceous species, releasing hydrogen in each of the steps. It can also be hydrogenated to ethane when adsorbed H is available. The rate of hydrogenation, however, is slower than the hydrogenation of ethylene on a Pt atom with preadsorbed H. In the presence of preadsorbed O, ethylene is oxidized to CO₂, H₂O, and CO via an intermediate that has a carbon-hydrogen stoichiometry of CH. The oxidation reaction takes place at the perimeter of the oxygen islands. The results suggest that decomposition, hydrogenation, and oxidation are independent pathways that can take place simultaneously depending on the availability of adsorbed H or O.