Density functional theory calculations are presented on the oxidation of ethene over Ti-silicate catalysts within the cluster approximation. Results using the BP86 functional and a DZVP basis suggest that, on interaction with hydrogen peroxide, a Ti(eta(2)-OOH) species is formed, which then donates an oxygen to a weakly bound alkene molecule. A number of different models for the Ti-IV site were used, and a number of different pathways were considered, e.g., different routes for the formation of the eta(2) complex, a route via formation of a Ti=O species and different possibilities for the interaction of the alkene with the Ti-IV site. Our calculated estimate of the activation barrier for oxidation, in good agreement with experiment, is around 70 kJ mol(-1). depending on the route followed. A mechanism for alkene oxidation over Ti-IV-silica catalysts in the presence of hydroperoxides is proposed, consistent with available experimental and theoretical data and including the effects on the reaction of different solvents, peroxides, additives, and bases.