(675f) Synthesis and Characterization of Au-Bimetallic Catalysts Prepared by Electroless Deposition Methods

Electroless deposition (ED) has been used for the preparation of continuous, thin film metal coatings, but also has the potential for the preparation of novel, bimetallic catalysts by adjustment of the deposition parameters. Unlike traditional methods for the preparation of bimetallic catalysts, ED permits the selective deposition of a secondary metal (in this case Au) on the surface of a catalytically active, primary metal surface. In order to prepare catalysts using this technique it is necessary to design a reactive, yet stable ED solution by the careful selection of the secondary metal salt and reducing agent(s), as well as the pH and temperature of the ED bath. In order to determine the stability and specificity of the bath, the ED solution is exposed to the support (in this case SiO₂) to ensure that neither metal salt adsorption nor spontaneous reduction and precipitation of the secondary metal from solution occurs. For the case of Pt/SiO₂ and Pd/SiO₂ , stable electroless solutions were developed using AuCl₂¯ and Au(CN)₂¯ as metal sources and HCHO and N₂H₄ as the reducing agents respectively. A series of Au-Pd/SiO₂ and Au-Pt/SiO₂ catalysts have been prepared and characterized using CO chemisorption and transmission electron microscopy, energy dispersed spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy of CO adsorption/desorption. A decrease in H₂ uptake on Pd and Pt coupled with changes in the population of adsorbed CO species with increasing Au content corroborate that the Au is being deposited on the primary metal. Analysis using EDS and XPS confirmed that supported nanoparticles had bimetallic compositions and that bimetallic electronic effects were present in some cases. These ED catalysts were also evaluated for hydrogenation of propylene and isopropanol oxidation as probe reactions. The efficacy of this ED approach for the synthesis of Au-Pd and other Au-containing catalysts will also be discussed.