title: Surface sites on Pt-CeO2 mixed oxide catalysts probed by CO adsorption: a synchrotron radiation photoelectron spectroscopy study.
abstract: By means of synchrotron radiation photoemission spectroscopy, we have investigated Pt-CeO2 mixed oxide films prepared on CeO2(111)/Cu(111). Using CO molecules as a probe, we associate the corresponding surface species with specific surface sites. This allows us to identify the changes in the composition and morphology of Pt-CeO2 mixed oxide films caused by annealing in an ultrahigh vacuum. Specifically, two peaks in C 1s spectra at 289.4 and 291.2 eV, associated with tridentate and bidentate carbonate species, are formed on the nanostructured stoichiometric CeO2 film. The peak at 290.5-291.0 eV in the C 1s spectra indicates the onset of restructuring, i.e. coarsening, of the Pt-CeO2 film. This peak is associated with a carbonate species formed near an oxygen vacancy. The onset of cerium oxide reduction is indicated by the peak at 287.8-288.0 eV associated with carbonite species formed near Ce(3+) cations. The development of surface species on the Pt-CeO2 mixed oxides suggests that restructuring of the films occurs above 300 K irrespective of Pt loadings. We do not find any adsorbed CO species associated with Pt(4+) or Pt(2+). The onset of Pt(2+) reduction is indicated by the peak at 286.9 eV in the C 1s spectra due to CO adsorption on metallic Pt particles. The thermal stability of Pt(2+) in Pt-CeO2 mixed oxide depends on Pt loading. We find excellent stability of Pt(2+) for 12% Pt content in the CeO2 film, whereas at a Pt concentration of 25% in the CeO2 film, a large fraction of the Pt(2+) is converted into metallic Pt particles above 300 K.
authors.affiliation: Lehrstuhl für Physikalische Chemie II, Friedrich-Alexander-Universität Erlangen-Nürnberg, Egerlandstrasse 3, 91058 Erlangen, Germany. yaroslava.lykhach@fau.de.
authors.forename: Armin
authors.initials: A
authors.lastname: Neitzel
authors.forename: Yaroslava
authors.initials: Y
authors.lastname: Lykhach
authors.forename: Tomáš
authors.initials: T
authors.lastname: Skála
authors.forename: Nataliya
authors.initials: N
authors.lastname: Tsud
authors.forename: Mykhailo
authors.initials: M
authors.lastname: Vorokhta
authors.forename: Daniel
authors.initials: D
authors.lastname: Mazur
authors.forename: Kevin C
authors.initials: KC
authors.lastname: Prince
authors.forename: Vladimír
authors.initials: V
authors.lastname: Matolín
authors.forename: Jörg
authors.initials: J
authors.lastname: Libuda