Synthesis and Catalytic Properties of Metal and Semiconductor Nanoclusters

Abstract

The synthesis of metal or semiconductor nanoclusters in the microheterogeneous environment of oil-continuous inverse micelle systems is discussed. We focus on the synthesis and catalytic properties of palladium, iron, and iron sulfide nanoclusters. Cluster size control is achieved by changing the micelle size. The size of various micelles used for synthesis was determined by small angle neutron scattering(SANS) and was chosen to produce cluster in the size range of 1–20 nm. Cluster sizes were determined by either transmission electron microscopy (TEM) or small-angle x-ray scattering (SAXS). Cluster structure was determined by either x-ray or electron diffraction. In the case of Fe nanoclusters the crystal structure depended on the chemical nature of the surfactant micelle used in the synthesis, illustrating the important role of the surfactant during the growth process. Results of in-situ pyrene hydrogenation using size-selected Pd clusters show a significant increase in activity/total surface area as the size decreases. These clusters also proved to be effective as unsupported catalysts for direct coal hydropyrolysis, even at very low metal concentrations. The synthesis and optical features of a new semiconductor cluster material, FeS₂ is discussed with regard to its use in photocatalysis. The application of FeS₂ in coal hydrogenolysis reactions has improved yields of short chain hydrocarbons significantly compared to conventional FeS₂ powders.