Reaction of SO2 with Cu/TiO2(1 1 0): Effects of size and metal-oxide interactions in the chemical activation of Cu nanoparticles

The reaction of SO2 with stoichiometric TiO2(1 1 0), partially reduced TiO2 − x(1 1 0) and Cu/TiO2(1 1 0) was investigated using synchrotron based X-ray photoemission spectroscopy. SO2 adsorbs on perfect TiO2(1 1 0) forming SO4 species at room temperature, while SO2 dissociatively adsorbs on partially reduced TiO2 − x(1 1 0) forming SO4, SO3 as well as two sulfide species. SO2 exposure to Cu particles supported on perfect TiO2(1 1 0) can lead to the formation of SO4, SO3 and sulfide species. When depositing Cu on SO4/TiO2(1 1 0) at room temperature, the dissociation efficiency of Cu atoms is much higher than that of Cu deposited on TiO2(1 1 0) prior to SO2 dosing. The post-deposited Cu atoms can efficiently contact and react with SO4 species before they form Cu-Cu bonds and big clusters. Small Cu nanoparticles supported on TiO2(1 1 0) are more reactive towards SO2 than surfaces of bulk copper. The chemical reactivity of the Cu/TiO2(1 1 0) system increases with Cu coverage until reaching a maximum at θCu = 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 SO2/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.