Adsorption and reaction of methanethiol on Pt(111)

Adsorption and thermal decomposition of H3CSH on Pt(111) is studied with temperature-programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS) with synchrotron radiation. A H3CSH molecule undergoes dehydrogenation via formation of HxCS (x <= 3) intermediates. The catalytic reactivity of Pt for dehydrogenation, which depends on interaction between the surface and the CHx moiety of HxCS, varies with coverage. At large coverage, H3CSH decomposes through desorbing hydrogen via stepwise dehydrogenation (H3CS -> H2CS -> HCS -> S + C). H2CS is proposed to be an intermediate for dehydrogenation of H3CS below 240 K, and subsequently undergoes disproportionation to form HCS with desorption of CH4 at 400 K. The HCS species further decomposes to desorb hydrogen at 475 K and to form C and S adatoms; these adatoms show a mixed (root 3 x root 3)R30 degrees and dim c(2 x 2) LEED pattern at saturation exposure. At small coverage, surface Pt exhibits a catalytic effect on dehydrogenation of HxCS via interaction of the CHx moiety with surface Pt atoms. Dehydrogenation of H3CSH is completed below 370 K and is proposed to form a surface C-S species; this species entirely decomposes to form C and S adatoms at 570 K. (c) 2005 Elsevier B.V. All rights reserved.