The thermal chemistry of iodobenzene on Pt(111)

The surface chemistry of iodobenzene (C6H5I) on Pt(111) 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(111) 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.