Visible-light-responsive photocatalytic reaction on tetrahedrally-coordinated chromium oxide moieties loaded on ZSM-5 zeolites and HMS mesoporous silica: partial oxidation of propane

Chromium oxide (Cr-oxide) moieties loaded on ZSM-5 zeolites and HMS mesoporous silica molecular sieves were prepared by an impregnation method and characterized by various spectroscopic methods (XRD, XAFS, UV-Vis, photoluminescence) and their photocatalytic reactivities for partial oxidation of propane under visible light irradiation were investigated. The local structure of Cr-oxide species depended to a large extent on the zeolite types and Si/A1 ratios of zeolites. Tetrahedrally-coordinated isolated Cr-oxide moieties can be loaded on HMS and ZSM-5 having the higher Si/A1 ratios. On these catalysts, in the presence of propane and O₂, a partial oxidation proceeded under visible light irradiation to produce acetone with high selectivity. The charge-transfer excited state of the tetrahedral Cr-oxide moieties plays a significant role in the selective photocatalytic reactions under visible light irradiation.