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

Niclas Johansson, Mie Andersen, Yuji Monya, Jesper N Andersen, Hiroshi Kondoh, Joachim Schnadt, Jan Knudsen

Research output: Contribution to journalArticlepeer-review


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
Issue number44
Publication statusPublished - 2017 Oct 5

Subject classification (UKÄ)

  • Condensed Matter Physics

Free keywords

  • CO oxidation
  • Ir(111)
  • Pt(111)
  • XPS
  • DFT


Dive into the research topics of 'Ambient pressure phase transitions over Ir(1 1 1): at the onset of CO oxidation'. Together they form a unique fingerprint.

Cite this