STUDY OF THE SURFACE-CHEMISTRY OF ETHYL GROUPS ON PT(111) BY USING PARTIALLY DEUTERATED ETHYL IODIDE

The surface chemistry of ethyl iodide was studied by using thermal programmed desorption (TPD) spectroscopy. Partially deuterated ethyl iodide molecules (CD3CH2I and CH3CD2I) were used to determine the mechanism for the reactivity of ethyl groups on the surface. Breaking of the C-I bond on Pt(111) at temperatures below 200 K results in the formation of ethyl moieties. Our thermal desorption experiments suggest that those ethyl groups dehydrogenate immediately after being formed to yield ethylene. Partial deuterium labeling on the ethyl moieties was used to demonstrate that such reaction occurs by elimination of a hydrogen atom in the β position (the farthest from the surface). Chemisorbed ethylene rehydrogenates at higher temperatures to form ethyl groups again, which then either hydrogenate immediately to form ethane or dehydrogenate back to ethylene (a mechanism responsible for H-D exchange). Additional experiments in which hydrogen or deuterium was coadsorbed with the ethyl iodide also help in elucidating the mechanism for the reactions involved. Finally, we used the kinetic information obtained with TPD to calculate the energetics of the surface steps studied here. © 1990 American Chemical Society.