Effects of Surface Defects and Coadsorbed Iodine on the Chemistry of Alkyl Groups on Copper Surfaces: Evidence for a Cage Effect

Article abstract of DOI:10.1021/j100053a036

The effects of defect sites and coadsorbed iodine atoms on the chemistry of alkyl groups with two to four carbon atoms on copper surfaces have been studied by temparature-programmed reaction (TPR).The primary reaction pathway for the adsorbed alkyl group both in the presence and absence of defects and iodine atoms is β-hydride elimination.Because desorption is not (under most conditions) the rate-determining step in the evolution of the product from the surface, the rate of the surface β-hydride elimination reaction could be monitored by TPR.Neither surface defects nor low coverages of coadsorbed iodine significantly affect the β-elimination rate.For high coverages of iodine, however, the rate of β-elimination by 5-10percent of the adsorbed alkyl groups is decreased by over five orders of magnitude (T_rxn = 385 K versus 230 K).The reaction kinetics together with observations from low-energy electron diffraction studies suggest that the dramatic inhibition of the β-elimination rate for high iodine coverages is due to cages of immobile iodine atoms that surround the alkyl groups and prohibit hydrogen transfer to the surface.