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Achaias, Greece

Zafeiratos S.,CNRS The Institute of Chemistry and Processes for Energy, Environment and Health | Paloukis F.,ICEHT FORTH | Papakonstantinou G.,ICEHT FORTH | Teschner D.,Fritz Haber Institute | And 9 more authors.
Catalysis Today | Year: 2010

In the present study the oxidation state and the surface composition of a ternary PtRuCo catalyst were investigated under methanol steam reforming (SRM) and water gas shift (WGS) reaction conditions at 570 K. Ambient pressure X-ray photoelectron spectroscopy (APPES) was applied in situ at 0.5 mbar, while simultaneously monitoring the catalytic activity of the sample by on-line mass spectrometry. Non-destructive depth profile measurements performed under SRM reaction conditions over a polycrystalline PtCo foil, were also used to obtain detailed depth-resolved information. The results showed that surface segregation of cobalt and modification of its oxidation state occurs when switching from SRM to WGS reaction conditions. Evidence of ionic Pt was found only during WGS reaction, while Ru was mainly present in the metallic state. The results clearly demonstrate the dynamic response of the PtRuCo catalytic surface to the reaction atmosphere. © 2010 Elsevier B.V. All rights reserved.

Jaksic J.M.,ICEHT FORTH | Labou D.,ICEHT FORTH | Lacnjevac C.M.,University of Belgrade | Siokou A.,ICEHT FORTH | And 2 more authors.
Applied Catalysis A: General | Year: 2010

Electrocatalytic peaks from potentiodynamic spectra for relevant electrode reactions have been employed to assess decisive and most important diagnostic criterions and parameters in the electrochemical promotion of heterogeneous catalysts (EPOC) and electrocatalysts. More specifically, the anodic oxidation of formaldehyde by the spillover supplied primary oxide of Pt (Pt-OH), both of them proceeding simultaneously as the fast reversible electrode processes of rather high faradaic yields, was investigated to estimate the relevance of catalytic peaks in cyclic voltammetry for the electrochemical promotion. In the same sense, catalytic potentiodynamic peaks have been used to prove and assess the entire spillover (or effusion) effect both of H-adatoms and the primary oxide itself, too, otherwise decisive for some significant electrochemical oxidation processes, such as CO tolerance and kinetics in the cathodic oxygen reduction (ORR), including electrocatalytic features of the latter, as the one of most important electrode reactions in aqueous media. The UPD and OPD spillover double layer charging and discharging properties of the primary oxide (M-OH), interrelated with the interactive self-catalytic effect of dipole-oriented water molecules, has also been pointed out. There has also been inferred that altervalent hypo-d-oxides impose spontaneous dissociative adsorption of water molecules and pronounced membrane spillover transferring properties instantaneously resulting with corresponding bronze type (Pt/H xWO 3) under cathodic, and/or its hydrated state (Pt/W(OH) 6), responsible for Pt-OH effusion under anodic polarization, this way establishing reversibly revertible alterpolar features (Pt/H 0.35WO 3 ↔Pt/W(OH) 6) and substantially advanced electrocatalytic properties of these composite interactive electrocatalysts. Such nanostructured type electrocatalysts, even of mixed hypo-d-oxide structure (Pt/H 0.35WO 3/TiO 2/C, Pt/H xNbO 3/TiO 2/C), have for the first time been synthesized by the sol-gel methods and shown rather high stability, distinctly pronounced electron conductivity and non-exchanged initial pure mono-bronze spillover and catalytic properties. © 2010 Elsevier B.V. All rights reserved.

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