Transient Structures of PdO during CO Oxidation over Pd(100)

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In situ high-energy surface X-ray diffraction was employed to determine the surface structure dynamics of a Pd(100) single crystal surface acting as a model catalyst to promote CO oxidation. The measurements were performed under semirealistic conditions, i.e., 100 mbar total gas pressure and 600 K sample temperature. The surface structure was studied in detail both in a steady gas flow and in a gradually changing gas composition with a time resolution of 0.5 s. The experimental technique allows for rapid reciprocal 1 space mapping providing the complete information on structural changes of a surface with unprecedented time resolution in harsh conditions. Our results show that the (root 5 x root 5)R27 degrees-PdO(101) surface oxide forms in a close to stoichiometric O-2 and CO gas mixture as the mass spectrometry indicates a transition to a highly active state with the reaction rate limited by the CO mass transfer to the Pd(100) surface. Using a low excess of O-2 in the gas stoichiometry, islands of bulk oxide grow epitaxially in the same (101) crystallographic orientation of the bulk PdO unit cell according to a Stranski Krastanov type of growth. The morphology of the islands is analyzed quantitatively. Upon further increase of the O-2 partial pressure a polycrystalline Pd oxide forms on the surface.


  • Mikhail Shipilin
  • Johan Gustafson
  • Chu Zhang
  • Lindsay Merte
  • Andreas Stierle
  • Uta Hejral
  • Uta Ruett
  • Olof Gutowski
  • Magnus Skoglundh
  • Per-Anders Carlsson
  • Edvin Lundgren
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Physical Chemistry
Original languageEnglish
Pages (from-to)15469-15476
JournalJournal of Physical Chemistry C
Issue number27
StatePublished - 2015
Publication categoryResearch