Immobilization of (n-Bu_4N)_4W_10O_32 on Mesoporous MCM-41 and Amorphous Silicas for Photocatalytic Oxidation of Cycloalkanes with Molecular Oxygen

摘要

Heterogenization of (n-Bu_4N)_4W_10O_32 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 N_2 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 cycclododecane 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-Bu_4N)_4W_10O_32 is not reduced after heterogenization; moreover, decautungstate 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.