Highly dispersed manganese oxide catalysts grafted on SBA-15: Synthesis, characterization and catalytic application in trans-stilbene epoxidation

Manganese oxide catalysts supported on mesoporous silica SBA-15 (Mn-SBA-15) were synthesized following a controlled post-synthesis grafting process through the atomic layer deposition. N₂-physisorption, X-ray diffraction, transmission electron microscopy, Raman spectroscopy, H₂ temperature-programmed reduction, diffuse reflectance UV-Vis, and X-ray absorption near-edge structure were employed to characterize the physicochemical properties. This grafting method can efficiently upload a large amount of Mn species, and the Mn-SBA-15 samples exhibited high surface area, large pore volume, and uniform pore size. The spectroscopic results revealed that the manganese oxides with the coexistence of Mn²⁺ and Mn³⁺ either highly dispersed on the mesoporous silica surface or formed small size MnO_x clusters in the SBA-15 channels depending on the manganese oxide contents. These manganese catalysts with ordered pore structure exhibited superior activity and selectivity towards desired product in the liquid-phase epoxidation of trans-stilbene using tert-butyl hydroperoxide as the oxidant.