title: Can the state of platinum species be unambiguously determined by the stretching frequency of an adsorbed CO probe molecule?
abstract: The paper addresses possible ambiguities in the determination of the state of platinum species by the stretching frequency of a CO probe, which is a common technique for characterization of platinum-containing catalytic systems. We present a comprehensive comparison of the available experimental data with our theoretical modeling (density functional) results of pertinent systems - platinum surfaces, nanoparticles and clusters as well as reduced or oxidized platinum moieties on a ceria support. Our results for CO adsorbed on-top on metallic Pt(0), with C-O vibrational frequencies in the region 2018-2077 cm(-1), suggest that a decrease of the coordination number of the platinum atom, to which CO is bound, by one lowers the CO frequency by about 7 cm(-1). This trend corroborates the Kappers-van der Maas correlation derived from the analysis of the experimental stretching frequency of CO adsorbed on platinum-containing samples on different supports. We also analyzed the effect of the charge of platinum species on the CO frequency. Based on the calculated vibrational frequencies of CO in various model systems, we concluded that the actual state of the platinum species may be mistaken based only on the measured value of the C-O vibrational frequency due to overlapping regions of frequencies corresponding to different types of species. In order to identify the actual state of platinum species one has to combine this powerful technique with other approaches.
authors.affiliation: Faculty of Chemistry and Pharmacy, University of Sofia, 1126 Sofia, Bulgaria. gnv@chem.uni-sofia.bg and Departament de Ciència de Materials i Química Física & Institut de Química Teòrica i Computacional, Universitat de Barcelona, 08028 Barcelona, Spain.
authors.forename: Hristiyan A
authors.initials: HA
authors.lastname: Aleksandrov
authors.affiliation: Departament de Ciència de Materials i Química Física & Institut de Química Teòrica i Computacional, Universitat de Barcelona, 08028 Barcelona, Spain and Institució Catalana de Recerca i Estudis Avançats (ICREA), 08010 Barcelona, Spain. konstantin.neyman@icrea.cat.
authors.forename: Konstantin M
authors.initials: KM
authors.lastname: Neyman
authors.affiliation: Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria.
authors.forename: Konstantin I
authors.initials: KI
authors.lastname: Hadjiivanov
authors.affiliation: Faculty of Chemistry and Pharmacy, University of Sofia, 1126 Sofia, Bulgaria. gnv@chem.uni-sofia.bg.
authors.forename: Georgi N
authors.initials: GN
authors.lastname: Vayssilov