The thermal chemistry of iodobenzene on Pt(111)

The surface chemistry of iodobenzene (C6H5I) on Pt(lll)has been studied by temperature-programmed desorption (TPD), X-ray photoelectron spectroscopy ( XPS), high resolution electron energy loss spectroscopy (HREELS) and isotop ic labeling. XPS results show that for the first layer C-I bond scission co mmences at 175 K. The phenyl fragment (C6H5) left after C-I bond cleavage l oses a hydrogen and forms an ortho-C6H4 (benzyne) intermediate. Upon furthe r annealing, the benzyne is rehydrogenated and forms benzene (C6H6), with h ydrogen supplied by the decomposition of other benzyne species. Formation o f benzyne involves a change in the adsorption geometry of the adsorbate adl ayer, which consequently opens new decomposition sites on the Pt(lll) and a llows the dissociation of approximately 70% of the second layer to occur. T he dissociation of the second layer leads to additional C6H6 formation via a coupling reaction of a phenyl fragment from the second layer and a surfac e hydrogen. The role that iodine plays on these reaction pathways and the i mplications of these results to the surface chemistry of benzene on transit ion metal surfaces are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.