Preparation and characterization of supported bimetallic Pt-Au and Pt-Cu catalysts from bimetallic molecular precursors

Silica-supported bimetallic Pt-Cu and Pt-Au catalysts were prepared using bimetallic molecular cluster precursors as the metal source to study the effects of added metal and precursor type on catalyst activity, selectivity, and structure. The molecular precursors were adsorbed on the support from an organic solvent, dried under vacuum, calcined under flowing oxygen, and reduced with hydrogen. The catalytic performance was assessed with hexane conversion reaction. The new catalysts were compared with conventionally prepared Pt and Pt-Cu catalysts, e.g., via wetness impregnation or coimpregnation, that were subjected to similar activation conditions. Both the 0.15-Pt₂Au₄ and 0.15-Pt₂Cu₄ catalysts had enhanced selectivity for the production of lighter hydrocarbons (cracking) and decreased activity for nondestructive alkane reforming and dehydrocyclization reactions. The diffuse reflectance FTIR spectra of CO adsorbed to the 0.15-Pt₂Cu₄ catalyst contained a very wide and asymmetric peak associated with CO bound to platinum. The differences in activity for skeletal rearrangements could be explained in terms of the cyclic mechanism of isomerization and supported the characterization data that very small and bimetallic particles are prepared using the cluster precursors.