QD115 : Preparation and Characterization of Schiff baxse Molybdenum Complexes Supported on Nano-Boehmite and Investigation of Its Catalytic Application
Thesis > Central Library of Shahrood University > Chemistry > MSc > 2012
Authors:
Adnis Amoli [Author], Bahram Bahramian[Supervisor], Mahdi Mirzaee[Supervisor]
Abstarct: The increasing environmental concern and promotion of “green processes” are forcing the substitution of traditional homogeneous catalysts by solid ones. Among the heterogeneous catalysts, nano-boehmite is a real “green” catalyst, due to their benign nature from an environmental point of view. In this research, nano-boehmite with high surface area (326m2/g) and high degree of surface hydroxyl groups, was prepared via hydrothermal assisted sol-gel processing of a 2 M solution of aluminum 2-butoxide in 2-butanol at 100°C for 5 hr (NB). The produced powder was filtered off, and covalently functionalized with 3-(tri-methoxysilyl)propyl amine by refluxing in dry toluene (AFNB). All the terminal amine groups of AFNB then were changed to imine by refluxing with salicylaldehyde in ethanol (IFNB). CHN analysis showed that the amount of amine and imine functionalizing group supported on AFNB and IFNB were 0.33 and 0.32 mmole/g respectively. Vanadium-oxo-sulfate and molybdenum hexa-carbonyl then supported on IFNB, by refluxing in ethanol and THF, respectively. ICP analysis showed that mextal loading on IFNB were 0.22 mmol/g for vanadium and 0.29 mmol/g for molybdenum, respectively. It confirmed also that over 65 and 90% of functionalized groups were mextalated with vanadium and molybdenum complexes, respectively. Furthermore, XRD patterns confirmed the retention of the nano-boehmite structure after functionalizing and mextal supporting procedures. These supported catalysts were used in epoxidation of cis-cyclooctene and yields of products were investigated by GC. The catalytic procedures for all catalysts were optimized for different parameters such as amount of catalyst (5, 10, 15, 20, 30 and 40mg), type of solvent (chloroform, dichloromethane, carbon tetrachloride, toluene, methanol, acetone and acetonitrile), amount of solvent (0, 1, 2, and 3ml carbon tetrachloride), type of oxidant (t-butyl-hydro-peroxide, hydrogen peroxide, urea-hydrogen peroxide and sodium periodate in carbon tetrachloride and acetonitrile), amount of oxidant (0.1, 0.15, 0.2, 0.3, 0.4, 0.5 and 0.6ml t-butyl-hydro-peroxide), temperature (25, 40 and 85°C) and time (30, 45, 60, 90, 120, 150, 180 and 210min). It was found that the optimized conditions with over 95% yield for epoxidation of 0.7mmol cis-cyclooctene with these heterogeneous nano-catalysts were 20 or 15mg of catalyst, 1ml carbon tetrachloride as solvent, and 1.4mmol t-butyl-hydro-peroxide as oxidant at 85ºC. The differences between these nano-catalysts were arisen on total time of catalytic process. The maximum yields were obtained after 120 and 210min, with Mo-IFNB and V-IFNB respectively. Therefore, among these two catalysts, Mo-IFNB can be chosen as the best because it was yielded the maximum efficiency in shorter period of time which is a crucial factor in scaling up the process to pilot plant. It must be noted that both of these nano-catalysts have over 90% yield without use of any solvent at the same conditions. In addition, recycling experiments revealed that these nano-catalysts could be repeatedly applied for nearly complete epoxidation of alkenes for at least five successive cycles.
Keywords:
#Heterogeneous Catalyst #Nano-Boehmite #Sol-Gel #Epoxidation #Cyclooctene #Molybdenum Complex #Vanadium Complex Link
Keeping place: Central Library of Shahrood University
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