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Silver nanosized particles were grown on the surface and in the channels of mesoporous silica (MCM-41) by stirring a mixture of AgNO3 and polyvinylpyrrolidone (PVP) in ethylene glycol in a 1 : 20 weight ratio with MCM-41 for 1 h. The heterogeneous product was analysed by BET surface area and X-ray powder diffraction measurements, as well as TEM images which indicated that 5 to 20 nm sized Ag particles were on the surface of MCM-41. The dried material, suspended in a mixture of 1,2-dichloroethane and acetonitrile and in the presence of tBuOOH held at 80 °C for 24 h, was capable of the oxidation of the olefins (Z)-cyclooctene, cyclohexene, styrene and indene resulting in a variety of oxidized products. Comparable oxidation was also accomplished in a green solvent mixture consisting of 3% NaCl dissolved in H2O and tBuOH (1 : 1 by volume). The catalyst was active for five sequential cycles. After the first cycle, H2O2 instead of tBuOOH could be used as the radical initiator as the Ag nanoparticles were passivated by the formation of AgCl on the surface. This research illustrates a method of oxygen activation allowing for the transfer of an oxygen atom from the atmosphere onto an olefin, presumably via the formation of a peroxide radical. [ABSTRACT FROM AUTHOR]