Enhanced transient reactivity of an O-sputtered Au(1Â 1Â 1) surface

The interaction of SO2 with oxygen-sputtered Au(1 1 1) (θoxygen ⩽ 0.35 ML) was studied by monitoring the oxygen and sulfur coverages as a function of SO2 exposure. The morphology of the sputtered Au is relatively smooth on a long length scale, but rough on a finer scale with islands averaging ∼15 nm. The rough surface is not stable to scanning with the STM. Two reaction regimes were observed: oxygen depletion followed by sulfur deposition. An enhanced, transient sulfur deposition rate is observed at the oxygen depletion point. This effect is specifically pronounced if the Au surface is continuously exposed to SO2. The enhanced reactivity towards S deposition seems to be linked to the presence of highly reactive, under-coordinated Au atoms. Adsorbed oxygen appears to stabilize, but also to block these sites. In absence of the stabilization effect of adsorbed oxygen, i.e. at the oxygen depletion point, the enhanced reactivity decays on a timescale of a few minutes. These observations shed a new light on the catalytic reactivity of highly dispersed gold nanoparticles.