This dissertation is focused on understanding heterogeneous bimetallic catalysts using model catalyst systems, such as Pd-Au/Mo(110), Pd/Au(111) and Pd/Au(100). Monometallic and bimetallic model catalysts, composed of Pd and Au, were prepared by physical vapor deposition (PVD) onto well-characterized metal substrates. Subsequent characterization was performed using an arsenal of modern surface science tools: low energy ion scattering spectroscopy (LEISS), infrared absorption spectroscopy (IRAS), temperature programmed desorption (TPD), and x-ray photoelectron spectroscopy (XPS). Electronic, morphological, and chemical properties of the prepared model catalysts were compared to those observed from monometallic single-crystal model catalysts such as Cu(100), Pd(111), Au(100), and Au(111). Between 700 K and 1000 K, formation of stable alloy surfaces of Pd-Au mixtures on Mo(110) was accompanied by substantial enrichment in Au. Annealing a 1:1 Pd-Au mixture at 800 K yields a Pd0.2Au0.8 surface alloy; the concentration of isolated Pd sites in this surface alloy can be systematically controlled by a judicious selection of initial bulk Pd-Au concentration. Pd-Au catalysts supported on Au(111) and Au(100) substrates generated a surface ensemble of Pd monomers surrounded by Au after annealing the systems at or above 550 K. To test the activity and selectivity of the prepared bimetallic model catalysts, the formation rate of vinyl acetate monomer (VAM) was examined. More significant enhancement of VAM formation rate was observed for bimetallic catalysts supported on Au(100) compared to those on Au(111). A critical surface ensemble composed two non-contiguous Pd monomers was proposed for the VAM synthesis. Oxygen plays a critical role in the efficiency of the synthetic route. Structure-reactivity correlations were established based on the suggested elementary reactions leading to the oxidative coupling of ethylene and acetic acid to form VAM.

SIMS est une technique d'analyse sensible de la surface. La probabilité d'ionisation dépend de l'état chimique de la surface. La génération des ions positifs est améliorée par le bombardement de la surface avec des éléments électronégatifs.Sur le NanoSIMS 50 de CAMECA, dont la configuration optique nécessite une polarité opposée entre ions primaires et secondaires, l'analyse des ions positifs se fait sous bombardement d'ions O-, générés dans un duoplasmatron. La faible brillance de la source en mode O- a comme conséquence une faible résolution latérale des analyses. Pour y remédier, nous avons étudié la possibilité de générer d’autres faisceaux d’ions primaires négatifs. Dans cet objectif, nous avons étudié la génération par duoplasmatron d'ions F-, Cl-, Br- et I- en fonction du champ magnétique, du courant d'arc et de la pression totale des gaz. Le courant d'ions et le diamètre du faisceau ont été mesurés afin de déterminer la brillance de la source en mode F-, Cl-, Br- et I-. Une brillance 5 fois plus élevée en mode F- qu'en mode O- a été déterminée.En utilisant les faisceaux F-, Cl-, Br- et I-, le rendement de pulvérisation, la concentration d'ions primaires implantés et le rendement utile ont été mesurés pour des semi-conducteurs et des métaux. Suite à une faible concentration en halogène à la surface des semi-conducteurs, résultant des processus de décapage, le rendement utile sous bombardement halogène était plus faible que sous bombardement O-. Pour les métaux (p.ex. Ni, Cu et Ag) par contre, une amélioration du rendement utile sous bombardement halogène jusqu'à deux ordres de grandeurs, comparé au bombardement O-, a été mesurée / Secondary Ion Mass spectrometry (SIMS) is a powerful surface analysis technique. The ionisation probability strongly depends on the chemical surface state. The generation of positive secondary ions can be enhanced by surface bombardment with electronegative elements.Due to the optical configuration of the CAMECA NanoSIMS 50, that necessitates an opposite polarity of incoming and ejected ions, analyses of positive ions are realized with primary O- ions, generated in a duoplasmatron ion source. As a consequence of the low O- brightness of the duoplasmatron source, the lateral resolution of the analyses on the NanoSIMS 50 is not satisfactory in the positive secondary mode. In this work, we studied the feasibility of different alternative negative primary ion beams. We investigated the possibility of F-, Cl-, Br- and I- ion generation with a duoplasmatron as a function of the source parameters, notably the magnetic field strength, the arc current and the total gas pressure. The ion current and the beam diameter were measured in order to determine the F-, Cl-, Br- and I- brightness of the source. A comparative study with the O- brightness demonstrates an increase of the F- brightness by a factor of 5.By using the F-, Cl-, Br- and I- bombardment, the sputtering yield, the concentration of implanted primary ions and the useful yield of different semi-conductor and metal samples were analysed. As a consequence of a low halogen concentration, related to etching effects, no enhancement of the useful yield could be noticed for the semi-conductors. For metals however (e.g. Ni, Cu and Ag), useful yield enhancements by up to a factor of 100 compared to the O- bombardment could be demonstrated