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 organometallic Pt-Au cluster precursor and compared with Pt and Pt-Au catalysts prepared by the incipient wetness impregnation of chloride salts. The supported catalyst precursors were calcined and reduced under identical conditions and the resulting catalysts were characterized with transmission electron 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 freshly supported precursors and after calcination. The bimetallic cluster precursor yielded catalysts with small (d ≈ 2.5 nm), uniform particles that have high Pt dispersion. EDS, CO chemisorption, and DRIFTS of adsorbed CO experiments gave strong evidence that these particles are bimetallic. Using the organometallic cluster precursor also caused a significant red shift (12 cm^-1) in the stretching frequency of adsorbed carbon monoxide relative to the traditional Pt catalyst. Catalytic performance was evaluated with the hexane conversion reaction. Results showed that the cluster-derived catalysts enhance the production of light hydrocarbons and decrease the rate of skeletal reforming reactions. Despite the enhancement of C-C bond fission reactions, catalysts prepared from the organometallic precursor had greatly enhancing resistance to deactivation. In contrast, the coimpregnation of Au with Pt from chloride salts yielded catalysts with little or no interaction between the two metals. For these catalysts, light hydrocarbon production decreased yet skeletal rearrangements were not measurably affected.