(442a) Synthesis and Characterization of Au-Pd/SiO2 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 this case Pd). 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 Pd/SiO₂, a stable, room temperature solution was obtained at basic conditions (pH 8-10) for two different electroless baths. One bath used AuCl₄^- as the metal source and HCHO as the reducing agent, while the second employed Au(CN)₂^- as the Au source and hydrazine as the reducing agent. For both systems, predictive, sub-monolayer coverages of Au on Pd were achieved. Thus, a series of Au-Pd/SiO₂ catalysts have been prepared and characterized using CO chemisorption and transmission Fourier-transform infrared (FT-IR) spectroscopy of CO adsorption/desorption. Chemisorption results show a decrease in CO uptake on Pd as Au is added, indicating Au deposition on Pd has occurred. Changes in the population of adsorbed CO species with increasing Au content also corroborate this finding. These catalysts were also characterized by HRTEM and XPS analysis. The efficacy of this ED approach for the synthesis of Au-Pd and other Au-containing catalysts will also be discussed.