Ambient pressure phase transitions over Ir(1 1 1): At the onset of CO oxidation

N. Johansson, M. Andersen, Y. Monya, J. N. Andersen, Hiroshi Kondoh, J. Schnadt, J. Knudsen

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2 Citations (Scopus)

Abstract

In this study we report on the adsorbate structures on an Ir(1 1 1) surface during the phase transition from the inactive to the active state during CO oxidation. The CO oxidation over Pt(1 1 1) is used as a reference case. Where Pt(1 1 1) either is inactive and CO covered or active and O covered, Ir(1 1 1) exhibits a transition state with co-existing chemisorbed O and CO. The observed structural differences are explained in terms of DFT-calculated adsorption energies. For Pt(1 1 1) the repulsive CO-O interaction makes co-existing chemisorbed CO and O unfavourable, while for Ir(1 1 1) the stronger O and CO adsorption allows for overcoming the repulsive interaction. At the onset of CO oxidation over Ir(1 1 1), a CO structure containing defects forms, which enables O2 to dissociatively adsorb on the Ir(1 1 1) surface, thus enabling the CO oxidation reaction. At the mass transfer limit, the Ir(1 1 1) surface is covered by a chemisorbed O structure with defects; hence, the active surface is predominately chemisorbed O covered at a total pressure of 0.5 mbar and no oxide formation is observed.

Original languageEnglish
Article number444002
JournalJournal of Physics Condensed Matter
Volume29
Issue number44
DOIs
Publication statusPublished - 2017 Oct 12

Keywords

  • APXPS
  • CO oxidation
  • DFT
  • Ir(1 1 1)
  • Pt(1 1 1)
  • XPS

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics

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    Johansson, N., Andersen, M., Monya, Y., Andersen, J. N., Kondoh, H., Schnadt, J., & Knudsen, J. (2017). Ambient pressure phase transitions over Ir(1 1 1): At the onset of CO oxidation. Journal of Physics Condensed Matter, 29(44), [444002]. https://doi.org/10.1088/1361-648X/aa8a44