259669 Synthesis, Characterization, and Evaluation of Supported Group IB-Pd Bimetallic Catalysts Prepared by Electroless Deposition Methods

Wednesday, October 31, 2012: 9:50 AM
319 (Convention Center )
John R. Monnier, Chemical Engineering, University of South Carolina, Columbia, SC

            Catalytic solutions are required for many of the economic and environmental issues facing the global community.  Alternative fuels and feed stocks, lower CO2 emissions, better exhaust emission control, and alternative sources of energy such as fuel cells all require new or improved catalysts.  These catalysts are likely to be bimetallic catalysts where bimetallic effects such as ensemble, electronic, and bi-functional effects can dramatically alter reactivity patterns.  The problem then becomes one of developing true bimetallic catalysts in a predictable manner and at potentially at large scales.  Conventional bimetallic catalysts are prepared by either simultaneous co-impregnation of both metal salts onto a catalyst support or successive steps of metal salt addition to typically form both bimetallic and undesired monometallic particles.  From a fundamental standpoint, it is very difficult to characterize such catalytic systems, and even more difficult to correlate catalyst performance with metallic composition.

            Electroless deposition (ED), however, is a process for the selective deposition of metallic components onto catalytically active sites through a controlled chemical reaction that is catalyzed by the pre-existing metal (catalysis) or the metal that itself is being deposited (auto-catalysis).  Whether catalytic or auto-catalytic deposition predominates is a function of the organic reducing agent (e.g., formaldehyde, borohydride, amine boranes, hydrazine, etc.), the reducible metal salt in solution, and the pre-existing, catalytic metal surface.  In principle, this method results in the selective deposition of the secondary metal only on the surface of a monometallic catalyst with no formation of isolated crystallites of the secondary metal on the catalyst support.  Consequently, ED offers many potential advantages over conventional impregnation-based preparation methods, since it provides significantly enhanced control over metal placement.

            In this presentation, examples and applications will be given for the preparation and characterization of supported Ag-Pd and Au-Pd catalysts that have been evaluated for the selective hydrogenation of acetylene in the presence of excess ethylene and the selective oxidation of glycerol, respectively.  The results will show that enhanced bimetallic effects occur at specific bimetallic surface compositions.


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