Design of Cr-oxide photocatalyst loaded on zeolites and mesoporous silica as a visible-light-sensitive photocatalyst

The photocatalytic reactivities of chromium oxide (Cr-oxide) loaded on zeolites and mesoporous molecular sieves by an impregnation method have been investigated. The Cr-oxide impregnated on mesoporous silica (imp-Cr/HMS) involves tetrahedrally-coordinated Cr-oxide moieties with two terminal Cr=O. The imp-Cr/zeolite contains a mixture of tetrahedrally- and octahedrally-coordinated Cr-oxide species (Cr2O3-like cluster). In the presence of propane and O2, a partial oxidation of propane with a high selectivity for acetone formation proceeded on imp-Cr/HMS under visible light irradiation, while a low reactivity was observed on imp-Cr/zeolites. The charge transfer excited state of the tetrahedrally-coordinated Cr-oxide moieties plays a significant role in the photocatalytic reactions.