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Träfflista för sökning "WFRF:(Chen W. M.) srt2:(1995-1999)"

Sökning: WFRF:(Chen W. M.) > (1995-1999)

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  • Chen, W., et al. (författare)
  • Redox properties of titanium oxides on Pt3Ti
  • 1995
  • Ingår i: Journal of Physical Chemistry. - : American Chemical Society (ACS). - 0022-3654 .- 1541-5740. ; 99:34, s. 12892-12895
  • Tidskriftsartikel (refereegranskat)abstract
    • The morphology and electronic structure of surface-segregated titanium oxides on Pt3Ti(111) are presented. Core level photoemission spectra at grazing emission reveal two states of oxidation: a dominant and reducible four-valent oxide together with a small amount of a three-valent oxide is produced by oxidation in 0 2 at and below 400°C; an irreducible three-valent oxide by oxidation in 02 at and above 450 °C. The ratio between the active four-valent and the inactive three-valent oxides decreases with increasing oxidation temperature. The probability for reduction by CO is almost unity for the Ti 4+ oxide, and the conclusion must be that the four-valent oxide plays an active role for catalytic reactions. Scanning tunneling measurements relate these observations to changes in the dispersion and nucleation of the oxide overlayer. The four-valent oxide grows as islands with remaining areas open for CO adsorption while the three-valent oxide spreads on and blocks the crystal surface. Photoemission spectra relate these dispersion effects to an electronic interaction between the Ti 3+ oxide and adjacent Pt atoms. The above observations are in accordance with the common picture of dispersion effects in titania-supported SMSI catalysts and prove that interfacial energies play a crucial role whether the dominant phase is metallic or an oxide.
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  • Pradier, C.M., et al. (författare)
  • NO reduction by isobutene, in the presence of oxygen, on platinum and copper : a comparative study
  • 1996
  • Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861 .- 1873-4308. ; 29:1-4, s. 59-65
  • Tidskriftsartikel (refereegranskat)abstract
    • The reaction of NO, oxygen and isobutene was studied under conditions close to stoichiometric, on a platinum and on a copper disk in order to better understand the role of each metal, free of any support and dispersion effects. The products of the reaction were analysed by mass spectrometry and an XPS characterization of the surface was carried out at different stages of the reaction. A correlation between the catalytic activity for NO conversion and the presence of adsorbed intermediates has been clearly demonstrated on platinum. On copper, a redox cycle of the metal is necessary to activate the catalyst. On platinum, oxygen is necessary to initiate the reaction, clean the surface and form reactive intermediates; the reaction is strongly sensitive to oxygen concentration, whereas on copper, oxygen does not directly participate in the reaction mechanism.
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