Active transition metal species (Co, Cu, Cr, Ni or Mn) supported on a chemically modified silica gel are used as heterogeneous catalysts in a range of Liquid phase oxidation reactions: alkyl aromatic side chain oxidations, epoxidations of alkenes and Baeyer-Villiger oxidations of linear ketones to esters and cyclic ketones to lactones. The catalyst employs metal centres bound to the silica surface via a hydrophobic spacer chain and is thus chemically robust and has a relatively high loading for a supported reagent (c 0.4mmolg(-1)). The Cr version of the catalyst promotes the oxidation of ethylbenzene to acetophenone in a solvent-free system at a rate of 5.5% h(-1) (>370 turnover h(-1)). It is also active for the oxidation of p-chlorotoluene and p-xylene to p-chlorobenzoic acid and p-toluic acid respectively. Cyclohexene is converted to its oxide at room temperature at a rate of c 28% h(-1) (c 12 turnover h(-1)) using either the Ni or Cu versions of the catalyst. The room temperature Baeyer-Villiger oxidation of cyclohexanone is achieved at a rate of 44% h(-1) (49 turnover h(-1)) using the Ni-containing catalyst. The same material also promotes the Baeyer-Villiger oxidation of linear aliphatic ketones and aromatic side chains. All the above systems use either air or molecular oxygen as the oxidant rather than peroxides or peracids.