| Summary: | Alloys, intermetallic compounds and multi-metal oxides are generally made by
traditional solid-state methods that often require melting or grinding/pressing powders
followed by high temperature annealing (> 1000 degrees C) for days or weeks. The research
presented here takes advantage of the fact that nanoparticles have a large fraction of their
atoms on the surface making them highly reactive and their small size virtually
eliminates the solid-solid diffusion process as the rate limiting step. Materials that
normally require high temperatures and long annealing times become more accessible at
relatively low-temperatures because of the increased interfacial contact between the
nanoparticle reactants.
Metal nanoparticles, formed via reduction of metal salts in an aqueous solution
and stabilized by PVP (polyvinylpyrrolidone), were mixed into nanoparticle composites
in stoichometric proportions. The composite mixtures were then annealed at relatively
low temperatures to form alloy and intermetallic compounds at or below 600 degrees C. This
method was further extended to synthesizing multi-metal oxide systems by annealing metal oxide nanoparticle composites hundreds of degrees lower than more traditional
methods.
Nanoparticles of Pt (supported or unsupported) were added to a metal salt
solution of tetraethylene glycol and heated to obtain alloy and intermetallic
nanoparticles. The supported intermetallic nanoparticles were tested as catalysts and
PtPb/Vulcan XC-72 showed enhanced catalytic activity for formic acid oxidation while
Pt3Sn/Vulcan XC-72 and Cu3Pt/y-Al2O3 catalyzed CO oxidiation at lower temperatures
than supported Pt.
Intermetallic nanoparticles of Pd were synthesized by conversion chemistry
methods previously mentioned and were supported on carbon and alumina. These
nanoparticles were tested for Suzuki cross-coupling reactions. However; the
homocoupled product was generally favored. The catalytic activity of Pd3Pb/y-Al2O3
was tested for the Heck reaction and gave results comparable to Pd/y-Al2O3 with a
slightly better selectivity.
Conversion chemistry techniques were used to convert Pt nanocubes into Ptbased
intermetallic nanocrystals in solution. It was discovered that aggregated clusters
of Pt nanoparticles were capable of converting to FePt3; however, when Pt nanocubes
were used the intermetallic phase did not form. Alternatively, it was possible to form
PtSn nanocubes by a conversion reaction with SnCl2.
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