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. The molecular precursors were adsorbed onto the support from an organic solvent, dried under vacuum, calcined under flowing oxygen, and reduced with hydrogen. The resulting catalysts were characterized with CO chemisorption, diffuse reflectance Fourier transform spectroscopy (DRIFTS) of adsorbed CO, transmission electron microscopy (TEM), and energy dispersive spectroscopy (EDS). The new catalysts were also compared to traditionally prepared Pt and Pt-Cu catalysts (wetness impregnation or coimpregnation) that had been subjected to identical activation conditions. When the molecular cluster precursors were used as catalyst precursors, small and uniform bimetallic particles with high Pt dispersions were prepared. The DRIFTS spectrum of CO bound to the cluster-derived Pt-Cu catalyst was exceptionally broad and indicated a large red shift in v(C equivalent to O) relative to Pt. Catalytic performance was evaluated with the hexane conversion reaction. Both cluster-derived catalysts showed enhanced selectivity for light hydrocarbon production (cracking) and decreased activity for nondestructive alkane reforming and dehydrocyclization reactions. The cluster-derived catalysts had nearly identical distributions of light hydrocarbon; these distributions indicated a propensity for internal C-C bond cleavage. Despite the similarities of these fission patterns, the Pt-Au catalyst had greatly enhanced resistance to deactivation processes while the Pt-Cu had no superior deactivation performance over the traditional Pt catalyst. (C) 2000 Academic Press.