Adsorption and thermally induced reactions of halocyclohexanes on a Cu 3Pt(1 1 1) surface

Abstract

The chemistry of iodocyclohexane, bromocyclohexane and chlorocyclohexane on a Cu 3Pt(1 1 1) surface has been investigated by temperature-programmed desorption (TPD), Auger electron spectroscopy (AES) and near-edge X-ray absorption fine structure (NEXAFS) measurements. Overall, the three halocyclohexanes undergo similar transformations on a Cu 3Pt(1 1 1) surface. C–I, C–Br and C–Cl bonds break between the corresponding temperatures on Cu(1 1 1) and Pt(1 1 1), leaving cyclohexyl species on the surface. The dehydrogenation reaction leading to the formation of benzene takes place at a very low coverage of cyclohexyl. As the surface concentration of halocyclohexane is increased, the dehydrogenation and hydrogenation of cyclohexyl leading to the formation of cyclohexane and cyclohexene dominates surface processes. The ratio of cyclohexene to cyclohexane produced during thermal annealing depends on the halogen involved. The lower C–X dissociation temperature for C–I, as compared to C–Cl and C–Br seems to favor cyclohexane formation. Molecular desorption of halocyclohexanes from monolayer and multilayer becomes significant at a higher dose. No surface carbon was found after thermal desorption under any coverage.