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 b imetallic molecular cluster precursors as the metal source. The molecular p recursors were adsorbed onto the support from an organic solvent, dried und er vacuum, calcined under flowing oxygen, and reduced with hydrogen. The re sulting catalysts were characterized with CO chemisorption, diffuse reflect ance Fourier transform spectroscopy (DRIFTS) of adsorbed CO, transmission e lectron microscopy (TEM), and energy dispersive spectroscopy (EDS). The new catalysts were also compared to traditionally prepared Pt and Pt-Cu cataly sts (wetness impregnation or coimpregnation) that had been subjected to ide ntical activation conditions. When the molecular cluster precursors were us ed as catalyst precursors, small and uniform bimetallic particles with high Pt dispersions were prepared. The DRIFTS spectrum of CO bound to the clust er-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 ev aluated with the hexane conversion reaction. Both cluster-derived catalysts showed enhanced selectivity for light hydrocarbon production (cracking) an d decreased activity for nondestructive alkane reforming and dehydrocycliza tion reactions. The cluster-derived catalysts had nearly identical distribu tions of light hydrocarbon; these distributions indicated a propensity for internal C-C bond cleavage. Despite the similarities of these fission patte rns, the Pt-Au catalyst had greatly enhanced resistance to deactivation pro cesses while the Pt-Cu had no superior deactivation performance over the tr aditional Pt catalyst. (C) 2000 Academic Press.