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 isotopic labeling. XPS results show that for the first layer C-I bond scission commences at 175 K. The phenyl fragment (C6H5) left after C-I bond cleavage loses a hydrogen and forms an ortho-C6H4 (benzyne) intermediate. Upon further annealing, the benzyne is rehydrogenated and forms benzene (C6H6), with hydrogen supplied by the decomposition of other benzyne species. Formation of benzyne involves a change in the adsorption geometry of the adsorbate adlayer, which consequently opens new decomposition sites on the Pt(lll) and allows the dissociation of approximately 70% of the second layer to occur. The dissociation of the second layer leads to additional C6H6 formation via a coupling reaction of a phenyl fragment from the second layer and a surface hydrogen. The role that iodine plays on these reaction pathways and the implications of these results to the surface chemistry of benzene on transition metal surfaces are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.