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SSCI-VIDE+ATARI+MAA:EEH:YJU:JBE; International audience; With the combination of various in-situ surface science tools, surface chemical and structural properties of bimetallic AuPd(1 1 0) alloys arecharacterized under elevated CO pressure. Under 1 Torr of CO gaspressure, STM images show the formation of nano-sized surfacerice-grains along the index direction of [1-10] while PM-IRRAS shows newCO vibrational band. This new vibrational band of PM-IRRAS is confirmedas the CO molecules attached to atop site of Pd with the results ofambient pressure XPS. In the case of adsorption of CO on AuPd(1 1 0)alloys, the so-called "pressure gap" exists and the surface morphologyand its chemical states change at elevated pressure conditions. (C) 2015Elsevier B.V. All rights reserved.

The reactivity of Pt3Sn(111) has been tested in the 1,3-butadiene hydrogenation reaction and compared to that of Pt(111) by a combination of polarization modulation absorption reflection infrared spectroscopy, mass spectroscopy and gas phase chromatography techniques. Pt3Sn(111) is less active than Pt(111) by one order of magnitude but it is more selective into butenes whatever the initial surface structure p ( 2 × 2 ) or ( 3 × 3 ).

Bond-order conservation-Morse potential (BOC-MP) model has been used to study the energetics of acrolein hydrogenation on Pt(1 1 1) and Ag(1 1 1) surfaces. For hydrogenation at low coverage of acrolein (θ=1/9), the model predicts an overall low activity for acrolein conversion and a lower selectivity for the formation of allyl alcohol. At higher acrolein coverage (θ=1/4), however, the total activity increases and the selectivity for the allyl alcohol is improved compared to its magnitude at low coverage. The results are in qualitative agreement with the experimental results on hydrogenation of similar α,β-unsaturated aldehyde on Pt surfaces indicating steric hindrance for the CC bond hydrogenation at higher coverages. As for hydrogenation on Ag(1 1 1) surface, the energetics predict relatively higher selectivity for allyl alcohol compared to the selectivity on Pt(1 1 1) surface. The predictions are critically discussed with reference to the available experimental results.

Two reactions, the hydrogenation of buta-1,3-diene on a Pd8Ni92(1 1 1) alloy and the hydrogenation of benzene on Pt(1 1 1), have been investigated under catalytic conditions by reflection absorption infrared spectroscopy (RAIRS). The purpose of this study was to use infrared spectroscopy to observe both the consumption/production of the different reactants/products and the adsorbed species present during the reaction. On Pd8Ni92(1 1 1), only butenes were produced during the buta-1,3-diene hydrogenation reaction up to the quasi-complete conversion of the diene, with a high rate of reaction. This alloy is therefore, active and very selective for such a reaction. In this case, no absorption bands corresponding to surface species were observed. Ad-species were observed during the benzene hydrogenation reaction on Pt(1 1 1); they cannot be attributed to chemisorbed molecular benzene, but are more probably due to partially hydrogenated intermediates, such as cyclohexadiene and/or cyclohexene.

Pd deposits on Ni(110) have been studied by low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), low-energy ion scattering spectroscopy (LEIS), and X-ray photoelectron spectroscopy techniques and their catalytic properties tested by the butadiene hydrogenation reaction at room temperature. Their catalytic activity is greatly enhanced by appropriate annealings. Superstructure indicative of a long range ordering of Pd atoms on Ni is evidenced for low Pd coverages neither before nor after annealing. For higher coverages, a LEED superstructure appears after annealing. AES and LEIS studies reveal a sharp Pd depth profile and the existence of a Pd–Ni surface alloy even at room temperature. The Pd 3d core level binding energy is shifted upwards by at least 0.4 eV with respect to pure Pd surface atoms and remains unchanged in the course of annealings. Hence geometrical rearrangements have to be taken into consideration to explain the activity enhancement.

Graphite powder electrodes bonded by polymerized LaPO4 have been investigated for the first time by atomic force microscopy (AFM). The interest in investigating this material stems from the fact that graphite electrodes intercalated, or not, with various metals and bonded with LaPO4 have shown very good mechanical and electrochemical stability during the hydrogen evolution reaction (HER) in 1 M KOH aqueous solutions. Examination of their surfaces by scanning electron microscopy has revealed that these electrodes are very porous. AFM furnishes additional data about the surface and can therefore be considered a powerful tool for surface characterization.

2 Dupont, C. Delbecq, F. Loffreda, D. Jugnet, Y.; An experimental evaluation, under realistic conditions, of the catalytic properties of a Pt3Sn(1 1 1) model catalyst in CO oxidation under excess of hydrogen is reported in this study. From a structural point of view, two different surface terminations are available in this alloy, viz. (2 x 2) and (root 3 x root 3)R30 degrees, differing by their tin concentration and Pt-Sn local structural arrangements in the uppermost layers, thus offering specific active sites for the reaction to proceed. In this study, mass spectrometry and polarization modulation infrared reflection absorption spectroscopy measurements (PM-IRRAS) have been performed at near ambient pressure on both surfaces of the alloy and compared to those obtained on Pt(1 1 1) used as a reference. The presence of hydrogen promotes the rate of CO oxidation on the three surfaces. The influence of tin is remarkable, increasing the catalytic activity of Pt atoms by one order of magnitude. With the exception of CO, no other species such as formyls or carbonates are observed on the surface by IR spectroscopy in the range of temperature (293-425 K) investigated. (C) 2010 Elsevier Inc. All rights reserved.

The gas phase selective hydrogenation of 1,3-butadiene was studied over Pd and Pd–Sn supported on mixed phase θ/α-(MA) and pure α-alumina (AA). The catalysts were characterized by XRD, XPS, TEM, and FTIR spectroscopy of adsorbed CO. A remarkable improvement in terms of activity and selectivity in the selective hydrogenation of 1,3-butadiene was achieved over Pd–Sn on the mixed phase alumina support in which butane formation and isomerization of 1-butene were suppressed. Nevertheless, Pd–Sn/AA showed much lower activity than Pd–Sn/MA due to lower metal dispersion.

Dupont, Celine Jugnet, Yvette Delbecq, Francoise Loffreda, David; The activation of oxygen reduction reaction fascinates numerous scientists in the fields of heterogeneous catalysis, electrochemistry and surface science. Indeed, oxygen dissociation is considered usually as the rate determining step of several reactions on conventional platinum catalysts. From combined experimental and theoretical approaches, we demonstrate comprehensively how tailored platinum-tin alloy surfaces allow to go beyond this chemical limitation. Near-ambient pressure kinetic measurements show the outstanding capacity of the Pt3Sn(111) single-crystal surfaces for carbon monoxide oxidation. The apparent activation energy is almost twice lower on the platinum-tin surface than on pure platinum catalyst. The theoretical analysis based on density functional theory calculations supports the idea that oxygen dissociation is never the rate determining step on these alloy surfaces since the corresponding rates calculated at room temperature always outstrip those of carbon monoxide oxidation. The influence of surface tin content and oxygen coverage on the activity is addressed in details. The mediatory role of tin in the alloy is elucidated on the basis of a charge transfer analysis. (C) 2010 Elsevier Inc. All rights reserved.

International audience; We present results from high-resolution electron energy loss spectroscopy (HREELS) and XPS studies of self-assembled monolayers of DNA. The monolayers are well-organized and display sharp vibrational peaks in the HREEL spectra. The electrons interact mainly with the backbone of the DNA. The XPS results indicate that, in most of the samples studied, the phosphates on the DNA are not charged.

A combination of GGA total-energy calculations and vibrational spectra simulations with HREELS experiments is reported to obtain new insights in the stable adsorption modes of the acrolein molecule on the Pt(111) surface. The simulations of the EELS spectra have allowed us to interpret the evolution of the experimental spectra, as a function of gas exposure. A strongly bound and coverage dependent chemisorption structure is shown. The 1 L spectrum has been assigned to a low coverage η3-cis and η4-trans mixed phase, with the molecule lying flat on the surface and interacting by both CC and CO bonds. The modified spectrum for an exposure of 2 L is associated with a change in the molecule adsorption structure toward a high coverage η2-cis and η2-trans form on the surface in complete agreement with the DFT total energy results.

We have studied the actinide superconductor U${\mathrm{Be}}_{13}$ with resonant photoemission using synchrotron radiation $30l~h\ensuremath{\nu}l~120$ eV. In agreement with the anomalously high $\ensuremath{\gamma}$ value of 1.1 J/mole ${\mathrm{K}}^{2}$, we find a high density of $5f$ states at the Fermi level ${E}_{F}$. Uranium $6d$ electrons are not present at ${E}_{F}$ as can be derived from the zero intensity at ${E}_{F}$ in the off-resonance spectrum. The close resemblance of this off-resonance curve to a photoemission spectrum of pure Be suggests that the hybridization of U $5f$ electrons with Be $s,p$ electrons is small. Indeed, the U${\mathrm{Be}}_{13}$ photoemission curves look like a superposition of U and Be curves. By using photoemission results from U${\mathrm{O}}_{2}$ as a reference, we find that the valence-band emission contains about one $5f$ electron. The present results on U${\mathrm{Be}}_{13}$ are compared with those of Ce${\mathrm{Cu}}_{2}$${\mathrm{Si}}_{2}$, another member of the family of exotic superconductors.