Synthesis and catalytic properties of metal and semiconductor nanoclusters.

摘要

Synthesis of metal or semiconductor nanoclusters in microheterogeneous oil-continuous inverse micelle systems is discussed. We focus on synthesis and catalytic properties of palladium, iron, and iron sulfide nanoclusters. Cluster size-control is achieved by changing the micelle size which is determined by small angle neutron scattering (SANS) and chosen to produce cluster in 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 effective as unsupported catalysts for direct coal hydropyrolysis, even at very low metal concentrations. Synthesis and optical features of a new semiconductor cluster material, FeS(sub 2), is discussed with regard to its use in photocatalysis. Application of FeS(sub 2) in coal hydrogenolysis reactions has improved yields of short chain hydrocarbons significantly compared to conventional FeS(sub 2) powders.