V-containing Mesoporous Molecular Sieves MCM-41: Synthesis, Characterization and Catalytic Oxidation

• Main Authors: Chih-Wei Chen, 陳志煒
• Other Authors: An-Nan Ko
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/69458816322540730980

碩士 === 東海大學 === 化學系 === 90 === Two types of vanadium-containing MCM-41 were synthesized via direct hydrothermal (V-MCM-41) and impregnation (V/MCM-41) methods. The catalysts were characterized by ICP-AES, XRD, N2-sorption, high temperature oxygen chemisorption (HTOC) measurements, 29Si and 51V NMR, TPR of H2, TPD of NH3 and FTIR techniques. The powder XRD patterns of all calcined samples exhibit characteristic MCM-41 structure. The 29Si NMR spectra of the calcined V-MCM-41 samples reveal similar patterns. Based on 51V NMR results, calcination followed by hydration in the air results in the transformation of tetrahedral V5+ into octahedral V5+ coordination due to addition of water molecules. For all samples, an increase of V content causes the decrease of surface area but enhances the amount of O2-chemisorption, the amount of weak acid sites in the NH3-TPD experiments and both the amount and the reduction temperature of H2 gas in the TPR experiments. The pyridine-FTIR investigations suggest the weak acid sites as Lewis acid sites which are associated with tetrahedrally coordinated vanadium. The catalysts were applied to a typical alkyl aromatic oxidation reaction of diphenylmethane (DPM) with tert-butyl hydroperoxide to produce benzophenone at 1 atm and 60℃ in a stirred batch reactor. The DPM conversion is proportional to the catalyst V content except at the highest V loading (9.1% V/MCM-41), probably due to its remarkably lower surface area. The acid amounts of these catalysts also affect the catalytic activity. Base on th results from NH3-TPD and pyridine-FTIR, the Lewis acid sites associated with vanadium are the major factor catalyzing the oxidation of diphenylmethane. Moreover, the catalysts were also utilized for the oxidation of fluorene, 9,10-dihydroanthracene and 4-nitroethylbenzene at benzylic position with excellent yields. In addition, the V-MCM-41 prepared with hydrothermal method was more active than V/MCM-41 prepared with impregnation. Leaching of active vanadium species from the silicate matrix during liquid phase reaction was found and the regenerate catalysts exhibited a slightly lose in its activity.