(428e) Synthesis, Characterization, and Evaluation of Supported Group IB-Pd Bimetallic Catalysts Prepared by Electroless Deposition Methods

            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.