A model study of alkali promotion of water-gas shift catalysts: Cs/Cu(111)

Charles T. Campbell, Bruce E. Koel

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Abstract

The kinetics of the forward water-gas shift reaction (H2O+CO→H2+CO2) have been measured on a Cs-doped Cu(111) single-crystal surface at pressures near 40 Torr. The Cs is dosed from aqueous CsOH solution and dried in air. The surface structures have been characterized by XPS, AES, LEED, and ISS both before and after reaction. The activity of the Cu(111) surface increases with increasing Cs coverage until it reaches a maximum at θCs{reversed tilde equals}0.13, where the rate is fifteen times that for Cs-free Cu(111). At higher coverages the rate decreases. The as-dosed surface is oxidized to Cu2O to a depth ≥20 Å. After brief treatments (<40 s) under reaction conditions, the surface is completely reduced to metallic Cu(111), with a Cs overlayer showing an O:Cs atomic ratio of about unity. This overlayer demonstrates a p(2×2) LEED pattern when θCs exceeds 0.13 (where the rate maximizes), which is interpreted in terms of islands of an oxidic or hydroxidic Cs overlayer of local coverage θCs=1/4. The promotion by Cs is attributed to a mechanism where the surface Cs/O complex participates directly in the dissociation of adsorbed H2O, which is the rate-determining step.

Original languageEnglish (US)
Pages (from-to)393-411
Number of pages19
JournalSurface Science
Volume186
Issue number3
DOIs
StatePublished - Aug 1 1987
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Materials Chemistry

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