Screening Study of Silica-Supported Catalysts for Photoepoxidation of Propene by Molecular Oxygen

To find systems that are effective for the photocatalytic epoxidation of propene by molecular oxygen, 50 types of silica-supported metal oxides were screened for photooxidation activity. Many elements on silica were found to be active for photooxidation, and the samples were classified according to activity. High selectivity for propene oxide (PO), but with a conversion as low as that of the silica, was observed on silica loaded with alkali metals (Li, and Na), alkaline-earth metals (Mg, Ca, Sr, and Ba), and rare-earth elements (Y and La). It seems that moderate electron negativity of elements improve the epoxidation selectivity on silica. Some elements (such as Ti, Zn, Pb, and Bi) on silica gave high yields of PO. The most effective systems, with high PO yields and low COx selectivity, were silica-supported Ti and Zn systems under the experimental conditions. Furthermore, photoepoxidation proceeds catalytically on the silica-supported Ti sample. High dispersion of metal oxides on the silica surface is an important factor for PO production in these systems.