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Synthesis, Characterization And Catalytic Activity Of Tungsten/Titanium-Containing Selective Oxidation Catalysts For Olefins

Posted on:2005-06-29Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y Y ChenFull Text:PDF
GTID:1101360155452365Subject:Organic Chemistry
Abstract/Summary:PDF Full Text Request
Selective oxidation of olefins with environmentally friendly method has longbeen a hot issue in organic synthesis field. Expectially, developing a catalyticsystem with high efficiency and easy work-up has attracted much attention ofchemists. So far there are two ideal systems with great potential, they arereaction-controlled phase transfer catalysis for epoxidation with heteropoly acidand epoxidation using titanium-containing materials as catalysts. In thedissertation, the reaction-controlled phase transfer catalysis system wassystematically studied by (31)P NMR, Raman and FT-IR methods. Subsequently, wesynthesized tungsten/titanium containing mesoporous materials and their catalyticperformances were investigated. The main results in this thesis are summarized asfollows:1. The 31P NMR, FT-IR and Raman results of reaction-controlled phasetransfer catalysts show that [π-C5H5N(CH2)15CH3]3[PW4O16] is a mixture ofheteropoly acid with different P/W ratio. After reaction with H2O2, active speciesfor epoxidation [(PO4){WO(O2)2}4]3- ,[(PO4){WO(O2)2}2{WO(O2)2(H2O)}]3-and [(PO3(OH)){WO(O2)2}2](2- were formed. When H2O2 was used up, the activeoxygen in the unit [W(O2)] was removed and these active species self-assembliedto the species with W-Ob-W and W-Oc-W similar to the species with Kegginstructure, which performed a process of reaction-controlled phase transfercatalysis. The P/W ratio and cation type have a great influence on the component,activity and recovery yield of these catalysts. The catalytic system also playsimportant role in the structure of recovered catalysts.2. A new catalytic system for oxygenation of cyclohexene/cyclohexanol/cyclohexanone to adipic acid was developed. In the system, 30%H2O2 and H3PW12O40 were used as oxygen source and catalyst, respectively, noorganic solvent was need. After the reaction, the product and catalysts can beseparated by simple cooling process. The optimal yield of adipic acid were79.2%,85.2%,89.3% for cyclohexanol, cyclohexanone, cyclohexene, respectively,and the puriety of product exceeded 98%. 3. Tungsten-containing mesoporous molecular sieves (W-SBA-15) have beensynthesized under conventional hydrothermal conditions in strong acidic solution,when the mixture of P123(EO20PO70EO20) and dodecyltrimethyl bromide (CTAB)was used as template. In the process, the tungsten in gel solution can beeffectively incorporated into the final W-SBA-15 materials and the tungstenspecies were highly dispersed. For the catalytic epoxidation of cyclohexene overthe W-SBA-15 materials, the conversion of cyclohexene could reach 59.0% andselectivity of epoxide was 99%. 4. High titanium-containing SBA-15 mesoporous molecular sieves have beensuccessfully synthesized by a prehydrolysis method. After prehydrolysis of TEOS,then TiCl3 was introduced, the titanium can be effectively incorporated into theframework of SBA-15 and exist in tetrahedral state. Mesoporous molecular sieveswith Ia3d structure (MS) with large pore and higher hydrothermal stability wassynthesized under conventional strong acidic hydrothermal conditions in thepresence of P123, using TEOS and PTES as silicon source. Titanium wasintroduced into the MS through liquid deposition method with tetra-n-butyltitanate as titanium source. The result of catalytic oxidation of styrene over theTi-SBA-15 and Ti-MS materials showed that they had higher catalytic activity.
Keywords/Search Tags:reaction-controlled phase transfer, epoxidation, adipic acid, W-SBA-15, Ti-SBA-15
PDF Full Text Request
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