Adsorption and dissociation of CO2 on a potassium-promoted Rh(111) surface

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Adsorption of CO2 on a clean Rh(111) surface has been found to be weak and non-dissociative. However preadsorbed potassium dramatically affected the behaviour of CO2 on Rh(111) and caused significant changes in the electron energy-loss spectrum of adsorbed CO2. (i) It increased the rate of adsorption of CO2; (ii) it induced the formation of strongly bonded CO2 species and (iii) it initiated the dissociation of CO2. While CO2 desorbs from a clean Rh(111) surface at 170-244K, in the presence of preadsorbed potassium ( < θK = 0.4) new adsorption states developed at 343 and 500 K. From a potassium coverage θK = 0.4 another high-temperature state appears with Tp = 714 K. At the same time potassium was stabilized by adsorbed CO2 on the surface; it desorbed in a narrow peak with T ≈ 720 K. The dissociation of CO2 was observed even at a low potassium coverage, θK = 0.03. The amount of CO formed and the peak temperature for CO desorption increased with increasing θK up to θK ≈ 0.25. The adsorption of CO2 on potassium-dosed Rh led to a significant work-function increase. This indicates a substantial charge transfer from the potassium-dosed metal to an empty CO2 π-orbital; as a result the bonding and structure of adsorbed CO2 are changed. The mutual stabilization of CO2 and K observed at higher K coverages is attributed to a direct interaction between CO2 and K and to the formation of carbonate-like species.

Original languageEnglish
Pages (from-to)2015-2033
Number of pages19
JournalJournal of the Chemical Society, Faraday Transactions 1: Physical Chemistry in Condensed Phases
Issue number7
Publication statusPublished - Dec 1 1987

ASJC Scopus subject areas

  • Chemistry(all)

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