Various ligand-stabilized metal nanoclusters as homogeneous and heterogeneous catalysts in the liquid phase

Ligand-stabilized noble metal nanoclusters, prepared by various chemical me thods by different research groups in Japan and Germany, were characterized and examined by a common method for application to the catalysis for hydro genation of olefins in homogeneous and heterogeneous systems in the liquid phase. The mean diameters of palladium, platinum, rhodium and Pd/Pt nanoclu sters stabilized by various ligands range from 1.3 to 3.2 nm if prepared by a single reaction, and from 2.2 to 4.0 nm if prepared by a stepwise growth method. The Stokes radii of metal nanoclusters stabilized by surfactants r ange from 1.7 to 2.1 nm, suggesting a thickness of the protective layer fro m 1.1 to 1.4 nm, whereas those stabilized by polymers give much larger valu es, suggesting the formation of aggregates. The catalytic activities of the metal nanoclusters, evaluated by hydrogenation of 1,3-cyclooctadiene and m ethyl acrylate, depend mainly upon the particle size, i.e. the smaller the size, the higher the activity, However, a strongly interacting ligand like tetraoctylammonium halide and 1,10-phenanthroline can disturb the hydrogena tion, In contrast, the activities of heterogeneous catalysts supported on c harcoal depend strongly on the covering strength of the stabilizer. Copyrig ht (C) 2001 John Wiley & Sons, Ltd.