H{sub 2}S adsorption on chromium, chromia, and gold/chromia surfaces: Photoemission studies
- Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973 (United States)
- Department of Physics, Tulane University, New Orleans, Louisiana 70118 (United States)
- Department of Physics, University of New Orleans, New Orleans, Louisiana 70148 (United States)
The reaction of H{sub 2}S with chromium, chromia, and Au/chromia films grown on a Pt(111) crystal has been investigated using synchrotron-based high-resolution photoemission spectroscopy. At 300 K, H{sub 2}S completely decomposes on polycrystalline chromium producing a chemisorbed layer of S that attenuates the Cr 3d valence features. No evidence was found for the formation of CrS{sub x} species. The dissociation of H{sub 2}S on Cr{sub 3}O{sub 4} and Cr{sub 2}O{sub 3} films at room temperature produces a decrease of 0.3{endash}0.8 eV in the work function of the surface and significant binding-energy shifts (0.2{endash}0.6 eV) in the Cr 3p core levels and Cr 3d features in the valence region. The rate of dissociation of H{sub 2}S increases following the sequence: Cr{sub 2}O{sub 3}{lt}Cr{sub 3}O{sub 4}{lt}Cr. For chromium, the density of states near the Fermi level is large, and these states offer a better match in energy for electron acceptor or donor interactions with the frontier orbitals of H{sub 2}S than the valence and conduction bands of the chromium oxides. This leads to a large dissociation probability for H{sub 2}S on the metal, and a low dissociation probability for the molecule on the oxides. In the case of Cr{sub 3}O{sub 4} and Cr{sub 2}O{sub 3}, there is a correlation between the size of the band gap in the oxide and its reactivity toward H{sub 2}S. The uptake of sulfur by the oxides significantly increases when they are {open_quotes}promoted{close_quotes} with gold. The Au/Cr{sub 2}O{sub 3} surfaces exhibit a unique electronic structure in the valence region and a larger ability to dissociate H{sub 2}S than polycrystalline Au or pure Cr{sub 2}O{sub 3}. The results of {ital ab initio} SCF calculations for the adsorption of H{sub 2}S on AuCr{sub 4}O{sub 6} and AuCr{sub 10}O{sub 15} clusters show a shift of electrons from the gold toward the oxide unit that enhances the strength of the Au(6s){leftrightarrow}H{sub 2}S(5a{sub 1},2b{sub 1}) bonding interactions and facilitates the decomposition of the molecule. (Abstract Truncated)
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- DOE Contract Number:
- AC02-76CH00016
- OSTI ID:
- 564879
- Journal Information:
- Journal of Chemical Physics, Vol. 107, Issue 21; Other Information: PBD: Dec 1997
- Country of Publication:
- United States
- Language:
- English
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