Structure and size of bimetallic palladium - Platinum clusters in an hydrotreatment catalyst

Highly dispersed supported bimetallic PdPt catalysts were prepared by incipient wetness co-impregnation of alumina with platinum bis-acetylacetonate Pt(Acac)(2) and palladium bis-acetylacetonate Pd(Acac)(2). The resulting Pt4Pd/Al2O3 and PtPd/Al2O3 catalytic systems dedicated to hydro-dearomatization in presence of sulfur were characterized by X-ray absorption spectroscopy, transmission electron microscopy and volumetric H2O2 titration. Direct structural evidence is given of the presence of nanometer bimetallic particles. Moreover, the complete set of results indicates a " cherry- like" structure for the bimetallic clusters with a preferential distribution of palladium atoms at the cluster stuface. Catalytic results shows that the optimum composition leading to the appropriate sulface structure must be adjusted as a function of the size of the clusters.