Pt-CO/SiO2 bimetallic planar model catalysts for selective hydrogenation of crotonaldehyde

Surface science models of silica-supported Pt-Co bimetallic catalysts with various Pt/Co ratios have been successfully prepared using the spin-coating technique. Platinum and cobalt loadings on a series of silica-supported model catalysts were quantified by Rutherford backscattering spectrometry. Atomic force microscopy images indicate that flattish layerlike structures were obtained in all cases. The electronic state of Co and Pt was investigated using X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS). NEXAFS shows that cobalt is mainly forming octahedrally coordinated Co2+ species in the unreduced catalysts. The formation of the active phase has been investigated by XPS and "in situ" soft X-ray absorption spectroscopy (XAS). The NEXAFS measurements performed under 1-2 mbar of H-2 reveal that cobalt is fully reduced to Co-0 at relatively low temperature in bimetallic catalysts and reveal a decrease of the electron density of Co as the Pt/(Pt + Co) ratio increases, indicating the formation of alloyed bimetallic particles. This is also supported by XPS measurements. The crotonaldehyde hydrogenation has been studied on planar surface science model catalyst under diffusion-limitation-free conditions in gas phase at atmospheric pressure and temperatures between 100 and 150 degreesC. The addition of Co significantly improved the selectivity toward crotyl alcohol. This improvement is correlated with the electronic properties of the active phase.