The effects of adsorbed sulfur on the adsorption and reaction of CO and methanol on Ni(100)

Abstract

The surface coverage of sulfur on Ni(100) was varied between 0 and 8.0×1014 atoms/cm2 in order to quantify its effect on both CO adsorption and CH3OH dehydrogenation as studied by temperature-programmed reaction spectroscopy. At a sulfur coverage of ns=4.8×104 atom/cm2 the CO desorption peak characteristic of clean Ni(100) was extinguished and was replaced by two distinct peaks at lower temperature (β1 and β2). Also at this coverage the methoxy intermediate became stable above room temperature, and the dehydrogenation selectivity shifted toward H2CO. At θs=0.38 only partial dehydrogenation of CH3OH to H2CO and H2 occured, and the amount of H2CO formed was maximized. It was found that CO preadsorbed into fourfold hollow sites poisoned the partial dehydrogenation in a one-to-one fashion by blocking formation of adsorbed methoxy intermediates. The results also indicate that short range interactions between adsorbed CO and S are not responsible for the sharp decrease in the saturation coverage of CO at low concentrations of adsorbed atomic sulfur.