(728f) Synthesis and Evaluation of Au-Pd/SiO2 Bimetallic Catalysts Prepared Using 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 (e.g., Au) on the surface of a catalytically active, primary metal surface (Pd). In order to prepare catalysts using this technique it is necessary to design a reactive, yet stable ED solution by the proper selection of the secondary metal salt and reducing agent(s), as well as the pH and temperature of the ED bath. The present ED bath uses Au(CN)₂^¯ as the Au source and hydrazine as the reducing agent. The optimum stable conditions (pH, concentrations of Au⁺ source and reducing agent) for electroless gold deposition were established. Thus, a series of Au-Pd/SiO₂ catalysts with increasing surface coverage of Au on Pd were prepared. These catalysts were structurally characterized using hydrogen titration of O-precovered Pd sites chemisorption methods and transmission FT-IR spectroscopy of CO adsorption, HRTEM/EDS and XPS techniques. The H₂-O₂ chemisorption results showed a decrease in H₂ uptake on Pd as Au was added, indicating Au deposition on Pd had occurred. Likewise, FTIR analysis suggests that Au is electrolessly deposited indiscriminately on all types of Pd sites. In addition, the Au-Pd bimetallic catalysts have lower Au 4f_7/2 binding energy compared to monometallic Au/SiO₂ suggesting electronic interactions between Au and Pd metals (i.e., the net electron transfer from Pd to Au). The Au-Pd bimetallic catalysts were evaluated using structure insensitive propylene hydrogenation probe reaction. As the Au coverage on Pd increased, the enhanced activity (10 to 15 times TOF-P based at >50% Pd coverage) suggests strong structural dependence on Au-Pd bimetallic surfaces. These Au-Pd bimetallic ensembles were employed to selectively hydrogenate trace amounts of acetylene in ethylene feeds which are used for PVP production. Finally, the Au-Pd bimetallic catalysts were used for liquid phase oxidation of glycerol, a biodeisel byproduct to form valuable chemical intermediates, such as glyceraldehyde, glyceric acid, hydroxyacetone, hydropyurvic acid, oxalic acid, and glycolic acid.