AVS 45th International Symposium
    Surface Science Division Thursday Sessions
       Session SS2-ThM

Paper SS2-ThM7
The Reaction of H@sub 2@S, S@sub 2@ and SO@sub 2@ with ZnO and Cu/ZnO Surfaces

Thursday, November 5, 1998, 10:20 am, Room 309

Session: Oxide Surface Chemistry
Presenter: J.A. Rodriguez, Brookhaven National Laboratory
Authors: S. Chaturvedi, Brookhaven National Laboratory
J.A. Rodriguez, Brookhaven National Laboratory
T. Jirsak, Brookhaven National Laboratory
J. Hrbek, Brookhaven National Laboratory
M. Kuhn, Brookhaven National Laboratory
Correspondent: Click to Email
The surface chemistry of H@sub 2@S, S@sub 2@ and SO@sub 2@ on polycrystalline ZnO and Cu/ZnO surfaces was investigated using synchrotron-based photoemission and ab initio SCF calculations. At 100 K, polycrystalline ZnO dissociates H@sub 2@S into HS, and the adsorbed HS species decompose at temperatures between 300 and 400 K leaving S atoms that are bonded to zinc sites of the oxide. By dosing S@sub 2@ to zinc oxide, one can generate a sulfur saturation coverage (0.7 ML) that is larger than that obtained after dosing H@sub 2@S (0.5 ML) and induce the formation of small amounts of SO@sub 3@ species on the surface. Possible reaction pathways for the dissociation of S@sub 2@ on ZnO(0001) and ZnO(1010) terraces were studied using ab initio SCF calculations. At low sulfur coverages, an adsorption complex in which S@sub 2@ is bridge bonded to two adjacent Zn atoms (Zn-S-S-Zn) is probably the precursor state for the dissociation of the molecule. H@sub 2@S and S@sub 2@ mainly react with the zinc sites of the oxide. In contrast, SO@sub 2@ preferentially bonds to oxygen forming a mixture of SO@sub 3@ and SO@sub 4@ at 100 K and pure SO@sub 4@ at 300 K. Results from ab initio SCF calculations indicate that SO@sub 2@ adsorbs on an oxygen site to form SO@sub 3@ which then extracts an oxygen from the ZnO lattice to form SO@sub 4@. The last step in this process has a substantial activation energy, and after dosing SO@sub 2@ to ZnO at 100 K a mixture of SO@sub 3@ and SO@sub 4@ is produced on the surface. Cu two-dimensional islands supported on ZnO show a band structure that is substantially different from that of pure metallic copper. The Cu/ZnO surfaces exhibit a reactivity towards H@sub 2@S and S@sub 2@ that is larger than that of ZnO but smaller than that of metallic copper.