Adsorption and reactivity of SO2 on Ir(1 1 1) and Rh(1 1 1)

The adsorption and reactivity of SO2 on the Ir(1 1 1) and Rh(1 1 1) surfaces were studied by surface science techniques. X-ray photoelectron spectroscopy measurements showed that SO2 was molecularly adsorbed on both the Ir(1 1 1) surface and the Rh(1 1 1) surface at 200 K. Adsorbed SO2 on the Ir(1 1 1) surface disproportionated to atomic sulfur and SO3 at 300 K, whereas adsorbed SO2 on the Rh(1 1 1) surface dissociated to atomic sulfur and oxygen above 250 K. Only atomic sulfur was present on both surfaces above 500 K, but the formation process and structure of the adsorbed atomic sulfur on Ir(1 1 1) were different from those on Rh(1 1 1). On Ir(1 1 1), atomic sulfur reacted with surface oxygen and was completely removed from the surface, whereas on Rh(1 1 1), sulfur did not react with oxygen.