Immobilization of (n-Bu4N)4W10O32 on Mesoporous MCM-41 and Amorphous Silicas for Photocatalytic Oxidation of Cycloalkanes with Molecular Oxygen

Heterogenization of (n-Bu4N)4W10O32 on amorphous and MCM-41 silicas by impregnation is a suitable method to prepare efficient and stable catalysts able to oxidize unactivated C–H bonds to the corresponding alcohols and ketones with molecular oxygen and near ultraviolet light. The thus-prepared catalysts were characterized by spectroscopic and N2 adsorption–desorption experiments. A better dispersion of decatungstate was achieved with MCM-41, which also has the higher surface area. Results obtained in the model photooxidation of cyclohexane and cyclododecane confirm that the decatungstate heterogenized on the more ordered MCM-41 silica promotes the process with higher chemoselectivity (cyclohexanone/cyclohexanol molar ratio=2.6). The photocatalytic efficiency of (n-Bu4N)4W10O32 is not reduced after heterogenization; moreover, decatungstate immobilized on amorphous silica oxidizes cyclododecane with a markedly higher efficiency than in the homogeneous phase. The supported photocatalysts can be used at least three times without any loss of activity.