Reaction of S{sub 2} and SO{sub 2} with Pd/Rh(111) surfaces: Effects of metal{endash}metal bonding on sulfur poisoning
- Department of Chemistry, Brookhaven National Laboratory, Upton, New York 11973 (United States)
The surface chemistry of S{sub 2} and SO{sub 2} on Rh(111), Pd/Rh(111) and polycrystalline Pd has been investigated using synchrotron-based high-resolution photoemission and {ital ab initio} self-consistent-field calculations. Pd adatoms lead to an increase in the rate of adsorption of S{sub 2} on Rh(111), but they are less reactive than atoms of pure metallic palladium: Rh(111){lt}Pd/Rh(111){lt}Pd. The adsorption of sulfur induces a large reduction in the density of states (DOS) near the Fermi level of Pd/Rh(111) surfaces. The decrease in the DOS is smaller than in S/Pd(111) but bigger than in S/Rh(111). The chemistry of SO{sub 2} on Rh(111), Pd/Rh(111), and Pd is rich. At 100 K, SO{sub 2} adsorbs molecularly on these systems. Above 200 K, the adsorbed SO{sub 2} decomposes (SO{sub 2,a}{r_arrow}S{sub a}+2O{sub a}) or transforms into SO{sub 3}/SO{sub 4} species. The molecular SO{sub x} species disappear upon annealing to 450 K and only atomic S and O remain on the surfaces. A Pd monolayer supported on Rh(111) is not very active for the dissociation of SO{sub 2}. In this respect, the Pd{sub 1.0}/Rh(111) system is less chemically active than pure Pd or Rh(111). The electronic perturbations associated with the Pd{endash}Rh bonds reduce the electron donor ability of Pd, weakening the interactions between the Pd 4d orbitals and the lowest unoccupied molecular orbitals of S{sub 2} and SO{sub 2}. The behavior of the S{sub 2}/Pd/Rh(111) and SO{sub 2}/Pd/Rh(111) systems shows that bimetallic bonding can reduce the reactivity of Pd towards sulfur-containing molecules. A very large drop in reactivity can be expected when Pd is bonded to {ital s,p} or early transition metals. {copyright} {ital 1999 American Institute of Physics.}
- OSTI ID:
- 295511
- Journal Information:
- Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 6 Vol. 110; ISSN JCPSA6; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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