Stable nanocluster catalysts prepared by chemical and gamma-radiolytic reduction methods were found to give very high turn-over frequency numbers in hydrogenation of styrene oxide and 2-butyne-1,4-diol (B3D) as compared to the conventional catalysts. A systematic study was carried out on the effects of different transition metals, their reduction methods, types of polymer used as a capping agent, and the concentration and composition of solvent used during catalyst preparation on the size and shape of nanoparticles. The reduction method of metal precursor directly influenced the morphology of the nanoparticles, affecting the catalyst activity considerably. The cubic-shaped nanoparticles (5-7 nm) were obtained in chemical reduction, while radiolytic reduction method gave spherical nanoparticles (1-7 nm). (C) 2004 Elsevier B.V. All rights reserved.