Surface Chemistry of SO2 on Zn and ZnO: Photoemission and Molecular Orbital Studies

Abstract

The reaction of SO2 with polycrystalline Zn and ZnO surfaces has been investigated using synchrotron-based high-resolution photoemission spectroscopy and ab initio self-consistent-field calculations. The chemistry of SO2 on Zn surfaces is quite complex and depends on both the temperature of adsorption and the SO2 exposure. At 300 K, SO2 dissociates on a clean Zn surface to form atomic sulfur and atomic oxygen (SO2,gas → Sa + 2Oa; SO2,gas → SOgas + Oa). The Zn ↔ SO2 bonding interactions induce a significant weakening of the S−O bonds. The theoretical calculations suggest the η2-O,O and η2-S,O bonding conformations of SO2 as the two possible precursors for the dissociation of the molecule. The dissociation reactions are much more exothermic than the formation of SO3 or SO4: SO2,gas + nOa → SOx, where x = 3 or 4. At high SO2 exposures (300 K), when most surface sites are blocked and dissociation of SO2 cannot occur, SO3 and SO4 are formed on the Zn surface. Adsorption at 100 K suppresses the SO2 dissociatio...