Adsorbate interactions on a Pt(110) surface. I. Sulfur and carbon monoxide

Abstract

The kinetics of H2S adsorption on a Pt(110) crystal at T = 240°C were investigated by Auger electron spectroscopy. The sticking coefficient of H2S on a clean surface was constant up to θ = 0.6 and estimated near unity while for θ > 0.6 it decreased to about 0.03. A series of LEED patterns characteristic of adsorbed sulfur was observed with increasing sulfur coverage. The adsorption behavior of CO on clean and partially sulfurized Pt(110) surfaces was studied by flash desorption techniques. The resulting desorption energies of CO on the clean Pt surface were 25.1, 28.7 and 31.4 kcal/mole. The partially sulfurized surfaces were characterized by several new CO binding states whose energies decreased with increasing sulfur coverage. A saturated Pt surface with a sulfur coverage of θ ≃ 0.75 did not adsorb any CO. The occurence of sulfur surface phases as defined by changes in the LEED pattern were correlated with the new binding states of CO. Thus the interaction between adsorbed CO and adsorbed sulfur is rather weak and does not lead to a surface reaction. The possible effects of adsorbed sulfur on the catalytic reactivity of Pt(110) are discussed in view of the present results.