(57o) Synthesis and Characterization of Gold-Platinum Bimetallic Catalyst Prepared by Electroless Deposition Method

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 the past, stable electroless solutions have been developed for temperatures close to room temperature (25^oC). Now, electroless solutions have also been studied for higher temperatures (60^oC) for deposition of Au on Pt/SiO₂. Stable electroless solutions have been developed using AuCl₄¯ and Au(CN)₂¯ as metal sources and HCHO and N₂H₄ as the reducing agents, respectively. In order to determine the stability and specificity of the bath, the ED solutions were 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 occurred. Thermodynamic stability of the bath over time has been assessed for the different bath compositions using UV-Vis Spectroscopy. Bath stability is observed to decrease over time and with increasing temperature and increasing reducing agent concentration and initial Au concentration. A series of Au-Pt/SiO₂ catalysts have been prepared and characterized using chemisorption (O₂-H₂ Titration). A decrease in H₂ uptake on Pt with increasing Au content corroborate that the Au is being deposited on the primary metal. Effects of temperature and composition in deposition and deposition rate have also been discussed.