Preparation, Characterization and Catalytic Activity of MgO/ SiO2 Supported Vanadium Oxide Based Catalysts

摘要

Vanadium oxide-based catalyst obtained by grafting VOCl3 on Florisil (MgO:SiO2) with the molar ratio of 15:85 have been studied for the selective oxidation of cyclohexane in order to obtain cyclohexyl hydroperoxide, cyclohexanol and cyclohexanone. The performances obtained have been compared with those of other catalysts in which vanadium oxide was supported on the same support by impregnation with ammonium oxalate. All the prepared catalysts have been characterized using XRD, FTIR, TEM, SEM, EDX, DRS and TGA in order to rationalize the differences in performance observed. The presence of magnesium oxide species (15 % MgO) on the surface of silica significantly modifies the molecular structure of the surface vanadium oxide species and changes their molecular structure from hydrated VO5/VO6 polymers to less polymerized VO4 species and/or isolated VO2(OH)_2 species. The catalytic activities indicate that the VO_x/Florisil catalysts show high conversions and TONs for those types containing isolated VO4. Compared to previously studied VO_x/SiO2 catalysts, the Florisil based systems show significantly improved leaching behavior.