Preparation and characterization of supported bimetallic Pt-Au particle catalysts from molecular cluster and chloride salt precursors

New silica-supported bimetallic Pt-Au catalysts were prepared using an orga nometallic Pt-Au cluster precursor and compared with Pt and Pt-Au catalysts prepared by the incipient wetness impregnation of chloride salts. The supp orted catalyst precursors were calcined and reduced under identical conditi ons and the resulting catalysts were characterized with transmission electr on microscopy (TEM), energy-dispersive spectroscopy (EDS), CO chemisorption , and diffuse reflectance infrared Fourier Transform spectroscopy (DRIFTS), Temperature-programmed reduction experiments were also performed on the fr eshly supported precursors and after calcination. The bimetallic cluster pr ecursor yielded catalysts with small (d approximate to 2.5 nm), uniform par ticles that have high Pt dispersion. EDS, CO chemisorption, and DRIFTS of a dsorbed CO experiments gave strong evidence that these particles are bimeta llic. Using the organometallic cluster precursor also caused a significant red shift (12 cm(-1)) in the stretching frequency of adsorbed carbon monoxi de relative to the traditional Pt catalyst. Catalytic performance was evalu ated with the hexane conversion reaction. Results showed that the cluster-d erived catalysts enhance the production of light hydrocarbons and decrease the rate of skeletal reforming reactions. Despite the enhancement of C-C bo nd fission reactions, catalysts prepared from the organometallic precursor had greatly enhancing resistance to deactivation. In contrast, the coimpreg nation of Au with Pt from chloride salts yielded catalysts with little or n o interaction between the two metals. For these catalysts, light hydrocarbo n production decreased yet skeletal rearrangements were not measurably affe cted. (C) 1999 Academic Press.