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Preparation of Heterogeneous Catalysts by Immobilization of Molybdenum and Manganese-shiff Base Complexes into the Nanopores of Zeolite and SBA-15

Zare, Maryam | 2013

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 44557 (03)
  4. University: Sharif University of Technology
  5. Department: Chemistry
  6. Advisor(s): Bagherzadeh, Mojtaba
  7. Abstract:
  8. This thesisconsiders new fundamental approaches to yield heterogeneous catalysts in to three sections. The first section described the immobilization of the molybdenum-Schiff base complexes in pores of SBA-15 in two different methodologies depending on the actual structure of the complexes., (i) stepwise formation of the complex by initial covalent anchoring of one of the components and consecutive solid phase synthesis consisting of the condensation of the other components of the salen complex (iii) one-step complex immobilization by covalent binding through the ligand.Based on the first methodology, we report the preparation of ordered mesoporous silica SBA-15 containing a molybdenum Schiff base complex anchored to the internal surface of pores by using two co-condensation routes A and B.The SBA-15 supports modified by an amine or salicylaldehyde were obtained by cocondensation of tetraethylorthosilicate and the corresponding organosilane in the presence of Pluronic P123 surfactant. The molybdenum-containing catalysts obtained in one of two ways show high activity and selectivity for the liquid-phase epoxidation of olefins with TBHP. Leaching tests and metal analysis of reaction solutions showed that the kinetically competent catalyst is the molybdenum complex immobilized on the internal surface of SBA-15 pores and there is no molybdenum species in the solution.In order direct immobilization of the salen-metal complex, dioxo and oxo-peroxo molybdenum complexes bearing a salicylidene 2-picoloyl hydrazone ligand have been synthesized and characterized. The complexes were evaluated for epoxidation catalysis with tert-buthylhydroperoxide (TBHP) and oxidation of sulfide. The MoO2(sal-phz) complex exhibited high catalytic activity for the epoxidation of olefins, whereas the peroxo analogue is inert to reaction with olefins, thus ruling out the peroxide compound as the intermediate responsible in the [MoO2(sal-phz)]-catalyzed epoxidation with TBHP. Oxidations of sulfides to sulfoxides by urea hydrogen peroxide (UHP) were efficiently enhanced with excellent selectivity under the catalytic influence of these complexes. A heterogenised version of the MoO2(sal-phz) complex was successfully obtained from the reaction of the molybdenum(VI) complex of salicylidene 2-picoloyl hydrazone with mesoporous silica containing 3-chloropropyl groups. Immobilization of the complex was carried out through covalent bonding between the chloropropyl group on the internal surface of pores and the pyridine ring nitrogen atom of salicylidene 2-picoloyl hydrazone ligand. Furthermore, the resulting hybrid material was found to be highly active catalyst in the liquid-phase epoxidation of olefins with TBHP as the oxygen source. Leaching tests and metal analysis of reaction solutions show that the catalytic activity stemmed from the immobilized species, not from the leaching of active species into solution.In the second part of this thesis, we have reported detailed synthesis and characterization of polymeric [MoO2(Salen)] complexes which form by combining MoO2(acac)2 and polymeric ligands bearing N2O2 cordination sites. The epoxidation of alkenes using tert-butylhydroperoxide (TBHP) and oxidation of sulfides to sulfoxides by urea hydrogen peroxide (UHP) were efficiently enhanced with excellent selectivity under the catalytic influence of these coordination polymers. The stability of polymeric catalysts was assessed by recycling a sample 5 times in both epoxidation and sulfoxidation. In the case of cyclooctene epoxidation, catalytic activity of [piperazinCH2{MoO2(Salen)}]n increased without losing the selectivity whereas the catalytic activity and selectivity of the spent catalyst decreased in sulfoxidation of methyl phenyl sulfide in consecutive runs. The last part, there is a report on transformation of a homogeneous catalyst into a heterogeneous one by encapsulation of a complex within the cages of a zeolite. The Mn-hydrazone Schiff base and encapsulated counterpart has been prepared and characterized by various methods. The catalysts showed excellent catalytic efficiency in epoxidation reactions with various olefinic compounds using TBHP as oxidant. Moreover, the encapsulatedcomplex showed good recoverability without significant loss of activity and selectivity at least 5 times
  9. Keywords:
  10. Molybdenum ; Immobilization ; Zeolite ; SBA Silica ; Catalytic Epoxidation ; Mesoporous Materials ; Tertiary Butylhydroperoxide (TBHP) ; Polymeric Complexes

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