Reaction of Deuterium Atoms with Cyclohexane on Cu(111): Hydrogen Abstraction Reactions by Eley-Rideal Mechanisms

Article abstract of DOI:10.1021/j100118a037

Cyclohexane desorbs molecularly intact from Cu(111) and does not react with deuterium atoms that are preadsorbed on the surface.By contrast, when deuterium atoms formed on a hot tungsten filament are impinged onto a Cu(111) surface precovered with cyclohexane, dehydrogenated products (cyclohexene, cyclohexadiene, and benzene) are evolved when the surface is heated in a subsequent temperature-programmed reaction (TPR) experiment.These D-atom-induced dehydrogenation products provide strong evidence for an Eley-Rideal mechanism where D atoms abstract hydrogen from cyclohexane prior to thermal accommodation with the surface.The kinetics of cyclohexene evolution indicate that both single and sequential H-atom abstractions occur by this mechanism.The cross section for abstraction is on the order of 0.5 Angstroem²/cyclohexane, about an order of magnitude smaller than that for D-atom addition to ?-bonds, consistent with the relative cross sections for these reactions in the gas phase.In addition to these Eley-Rideal-type reactions, there is evidence for Langmuir-Hinshelwood hydrogenation and dehydrogenation reactions during the TPR experiment.Product distributions in the desorbing flux were quantified by mass spectrometry using an electron-impact ionization energy of 15 eV to accentuate the molecular ions.