Adsorption of benzene on ordered Sn/Pt(1 1 1) surface alloys

The adsorption of benzene (C6H6) on Pt(1 1 1) and two Sn/Pt(1 1 1) surface alloys has been investigated using high resolution electron energy loss spectroscopy, ultraviolet photoelectron spectroscopy and temperature programmed desorption. The two ordered Sn/Pt(1 1 1) alloys were prepared by annealing a thin Sn film deposited onto Pt(1 1 1). Depending on the temperature of annealing the surface exhibited a (2×2) or (3×3)R30° LEED pattern corresponding to a surface composition of Pt3Sn and Pt2Sn, respectively. At temperatures below 350 K benzene adsorbs intact on the pure Pt(1 1 1) surface. The molecule is π-bonded with its ring parallel to the substrate. Upon heating part of the benzene desorbs and the remaining amount dehydrogenates to carbon. On both Sn/Pt(1 1 1) alloys benzene is physisorbed and the decomposition is completely suppressed.