Selective oxidation of styrene over transition metal-doped mesoporous silica catalyst.

An inverse-micelle sol-gel method was used to prepare Ti and Fe-doped mesoporous silica catalysts, and they were utilized for selective oxidation of styrene to benzaldehyde. The amorphous peak of silica was confirmed by XRD and there were no peaks related to Ti or Fe oxides. Results indicate that the metals were homogeneously distributed in the silica matrix, leading to higher surface area and pore volume. Introduction of Ti species into mesoporous silica improved the total catalyst acidity and catalytic data revealed that the oxidation activity of Ti-doped mesoporous silica (Ti-MS) catalyst achieved 93% styrene conversion and 91% benzaldehyde selectivity under optimized conditions. Formic acid, phenylacetaldehyde, acetophenone and epoxy-styrene are all minor products of this reaction. The acid strength and the use of appropriate solvents and oxidants are crucial to achieving high styrene conversion and benzaldehyde yield. The catalysts were reusable up to 4 cycles without loss of activity.