Preparation of carbon-supported, bimetallic nanocomposites from single-source molecular precursors

Single-phase, carbon-supported Pt₁Sn₁ and Pt₁Ru₁ bimetallic nanoparticles with diameters ranging from 3 to 26 nm were prepared via thermolysis of single-source molecular precursors deposited on a graphitic carbon support. A novel technique to thermally degrade and reduce molecular and ionic metal precursors using the dielectric loss heating that is experienced by conductive carbons upon exposure to microwave irradiation was developed. Pt₁Ru₁ nanoclusters supported on graphitic carbon prepared using dielectric loss heating demonstrate an unprecedented methanol oxidation activity for supported catalysts with a relative performance that is comparable to that of the best unsupported Pt₁Ru ₁ catalyst currently available. On-particle energy dispersive spectroscopy (EDS) analysis of these systems was used to determine the compositional variability among the nanoparticles. For the PtSn/carbon nanocomposite, all of the nanoparticles that were analyzed had metal stoichiometries consistent with the formation of the hexagonal Pt₁Sn₁ (niggliite) intermetallic alloy phase. For the PtRu/carbon nanocomposites, local heating effects induced by the high flux electron beam used for on-particle EDS analysis caused an apparent loss of volatile ruthenium oxides formed at the surfaces of the nanoparticles, and concomitant alteration of the measured metal stoichiometry. A mathematical model was developed to compensate for the loss of volatile metal oxides from nanoparticle surfaces. A close agreement between predicted and experimentally measured nanoparticle oxide coverage validates this particular computational approach.