Reaction of SO 2 with Cu/TiO 2(1 1 0): Effects of size and metal-oxide interactions in the chemical activation of Cu nanoparticles

Abstract

The reaction of SO 2 with stoichiometric TiO 2(1 1 0), partially reduced TiO 2 − x (1 1 0) and Cu/TiO 2(1 1 0) was investigated using synchrotron based X-ray photoemission spectroscopy. SO 2 adsorbs on perfect TiO 2(1 1 0) forming SO 4 species at room temperature, while SO 2 dissociatively adsorbs on partially reduced TiO 2 − x (1 1 0) forming SO 4, SO 3 as well as two sulfide species. SO 2 exposure to Cu particles supported on perfect TiO 2(1 1 0) can lead to the formation of SO 4, SO 3 and sulfide species. When depositing Cu on SO 4/TiO 2(1 1 0) at room temperature, the dissociation efficiency of Cu atoms is much higher than that of Cu deposited on TiO 2(1 1 0) prior to SO 2 dosing. The post-deposited Cu atoms can efficiently contact and react with SO 4 species before they form Cu–Cu bonds and big clusters. Small Cu nanoparticles supported on TiO 2(1 1 0) are more reactive towards SO 2 than surfaces of bulk copper. The chemical reactivity of the Cu/TiO 2(1 1 0) system increases with Cu coverage until reaching a maximum at θ Cu = 0.5–0.8 ML. After this point, an increase in Cu coverage leads to the formation of big Cu particles and the reactivity of the system decrease to that typical of bulk Cu. A comparison with results for SO 2/Cu/MgO(0 0 1) indicates that the effects of size and metal ↔ oxide interactions are important for the chemical activation of Cu nanoparticles on titania.