Quantum Chemical Study of the Mechanism of Partial Oxidation Reactivity in Titanosilicate Catalysts: Active Site Formation, Oxygen Transfer, and Catalyst Deactivation

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(η2-OOH) species is formed, which then donates an oxygen to a weakly bound alkene molecule. A number of different models for the TiIV site were used, and a number of different pathways were considered, e.g., different routes for the formation of the η2 complex, a route via formation of a TiO species and different possibilities for the interaction of the alkene with the TiIV 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 TiIV−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, ...