Single-Step, Plasma-Based Synthesis of Supported Nanoparticle Catalysts

Many established and future technologies rely on the unique chemical and opto-electronic properties of nanometer-scale particles. For example, metal, metal oxide, and semiconductor nanoparticles find application in heterogeneous catalysis, photocatalysis, and photovoltaics. In light of such needs, a robust synthesis route for size and composition-controlled nanoparticles would be highly desirable.

In this work, we present a single-step, plasma-based synthesis route to produce a wide range of surfactant-free nanoparticles (e.g. metals, alloys, metal oxides, oxide-supported metals, and semiconductors) in the 1-20 nm size range that can be used in catalytic applications. A hydrodynamically-stabilized, atmospheric pressure, micro-hollow cathode plasma discharge with high density and temperature is used to pyrolyze volatile organometallics and semiconductor precursors to nucleate small crystalline nanoparticles. Particle growth is quenched at small, uniform size because the residence time in the plasma is very short (~microseconds). The end result is an aerosol of surfactant-free nanoparticles that can be spray-deposited on a variety of surfaces.

The talk will focus on the synthesis and characterization of metallic (Pd, Fe, Ni), alloy (Pd-Ag, Fe-Ni), and oxide-supported metallic nanoparticles (Pd/SiO₂) realized via microplasma deposition. In-situ FTIR and catalytic testing of Pd and Pd/SiO₂ for selective hydrogenation and CO oxidation were performed to probe activity and metal-support interactions. With respect to hydrogenation, both Pd catalysts exhibited low temperature light-off (< 70 deg C) and high ethylene selectivity at high conversion. Pd catalysts spray-deposited on ITO and graphitic supports were also tested for electrochemical oxidation of methanol and formic acid. Finally, we will highlight how microplasmas can be used to realize a variety of nanostructured materials for various technological applications.