Bauer, John C. (2009-05). Nanoparticles as Reactive Precursors: Synthesis of Alloys, Intermetallic Compounds, and Multi-Metal Oxides Through Low-Temperature Annealing and Conversion Chemistry. Doctoral Dissertation. Thesis uri icon

abstract

  • 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.
  • 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.

publication date

  • May 2009