Ag nanoparticles have been prepared by gamma-radiolysis of AgNO3 in aqueous matrix of SiO2 (Aerosil 200) in the presence of 2-propanol as OH radical scavenger. The presence of SiO2 prevents rapid agglomeration of Ag and the Ag nanoparticles formed become attached to SiO2. Transmission electron microscope (TEM), XRD and UV-vis measurements have shown that by adjusting the SiO2/solvent ratio the size of Ag nanoparticles can be controlled. Decreasing solvent/SiO2 ratio and high dose rate facilitated formation of small particles of 2-6 nm on SiO2. The in situ generation of Ag particles on silica has been attributed to the participation of solvated electrons formed at the silica/solvent interfacial layer. The Ag/SiO2 catalysts were tested in transformation of styrene oxide in hydrogen/He stream. The main reaction pathway is removal of oxygen. The low yield of aldehyde and alcohol can be attributed to low surface coverage of hydrogen on Ag. (c) 2005 Elsevier B.V. All rights reserved.