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Synthesis,Characterization Of Molecular Sieve With High Heteroatom Content And Its Catalytic Performance

Posted on:2015-04-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:K WuFull Text:PDF
GTID:1221330467471168Subject:Chemical Engineering and Technology
Abstract/Summary:PDF Full Text Request
Porous materials play an important role as catalysts and catalyst supports in the field of petrochemical industry, adsorbent materials and purification of the waste water. According to the definition of the IUPAC, porous materials can be divided into three classes:microporous materials (<2nm), mesoporous materials (2-50nm), and macroporous materials (>50nm). In the family of microporous materials, the best known members are zeolites which have uniform micropore size distribution and good hydrothermal stability.Catalyst is the most important functional materials in chemical industry, which is the irreplaceable role in the production of various types of chemicals. In recent years, the preparation of high efficiency and green catalytic materials has become one of the hotspots in research of catalyst. In this respect, zeolite porous materials reveal a good prospect. However, zeolites present severe limitations due to micropore size when large reactant molecules are involved, especially in fine chemicals, preparation of mesoporous structure of the zeolite molecular sieves was found to be an effective method to solve this problem. However, weak acidity and lower hydrothermal stability restrict the pure silica mesoporous materials application in the field of petroleum chemical industry. The incorporation of heteroatom into the framework and the optimization of molecular sieve reaction conditionscan can significantly promote the acidity and hydrothermal stability, moreover the content and the position of heteroatoms in the framewok can directly determines the molecular sieve acidity, ion exchange capacity and redox properties. The studies realized the incorporation of two or more different metals might create different or new redox and acid properties. However, only a few studies concern the synthesis of bimetallic mesoporous molecular sieves.In this paper, we show that high content of transition metal was successfully incorporated into mesoporous molecular sieves using the associated matter of ionic complex and structure-directing agent as template. All of the samples were characterized by using X-ray fluorescence spectroscopy, X-ray diffraction, small-angle x-ray scattering scanning, electron microscopy, high-power transmission electron microscopy, N2adsorption-desorption, thermogravimetric-differential scanning calorimetry, infrared absorption spectroscopy, H2temperature-programmed desorption, UV-visible absorption spectroscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, X-ray absorption fine structure. Moreover, the catalytic performance of the samples were investigated through the hydro xylation of benzene, the selective oxidation cyclohexane and the hydro xylation of phenol. The main research results are as following:(1) The mesoporous MFI molecular sieve with high iron content was prepared by potassium ferricyanide and TBAB as template. The characterization results showed that the preparation of samples retained high crystallinity and the iron atoms in the form of TO4distributed in the skeleton structure of molecular sieve. When the iron content was7.2wt%, the specific surface area of the sample was453m2/g and the diameter was2.68nm. According to the characterization results, the formation mechanism of the samples was described. Phenol hydroxylation as a probe reaction investigated the catalytic properties of the samples under80℃reaction temperature and6h reaction time, the results showed that the catalytic performance increased with the increase of iron content. When the iron content was7.2wt%, phenol conversion could be up to56.7%, and the product selectivity of catechol and hydroquinone was73.4%.(2) High iron content of Fe-MCM-41was successfully prepared by hydro thermal method using tartaric acid as complexing agents. The characterization results showed that the iron atoms in the form of TO4presented in the MCM-41framework when the content of iron was11.8wt%and the samples possessed relatively ordered mesoporous hexagonal structure. The specific surface area of the sample was987m2/g and the diameter was3.84nm. When the iron content was13.2wt%, the excess iron in the form of oxide dispersed the MCM-41channels. The catalytic performance was investigated with oxidative desulfurization under50℃reaction temperature and1h reaction time. Desulfurization effect increased with increasing iron content, when the iron content was11.8wt%, the desulfurization effect could be up to99%.(3) The V-MCM-41was prepared using tartaric acid as complexing agents. The characterization results revealed that the vanadium atom in the framework was8.1wt%and the obtained samples retained the hexagonal mesoporous structure. When the vanadium content was8.1wt%, the specific surface area of the sample was692 m2/g and the diameter was4.6nm. V-MCM-41revealed excellently catalytic performance in the selective oxidation cyclohexane reaction using H2O2as oxidant under70℃reaction temperature and7h reaction time. The cyclohexane conversion was22.57%, and the selectivity of cyclohexanol and cyclohexanone (KA oil) was99.53%. According to the catalytic performance results, we proposed a mechanism of selective oxidation cyclohexane to explain the reason of cyclohexanone and cyclohexanol ratio about2:1.(4) Combining the hydrothermal crystallization and evaporation induced self-assembly methods to make up for their shortcomings, high vanadium content V-SBA-16molecular sieve was successfully prepared. The characterization results revealed that the obtained samples possessed3D cubic structure. When the vanadium content was9.3wt%. the specific surface area of the sample was452m2/g and the diameter was4.3nm. The samples revealed excellently catalytic activity in hydro xylation of benzene and the catalytic performance increased with the increase of iron content under30℃reaction temperature and4h reaction time. When the vanadium content was9.3wt%, the optimum of benzene conversion was25.6%and the selectivityof phenol was86.6%.(5) The bimetallic silicate molecular sieves have been prepared by direct hydrothermal synthesis. The different sequence of vanadium and titanium sources can directly affect the formation of high content bimetallic mesoporous molecular during synthesis. The characterization results revealed that the obtained samples possessed2D hexagonal mesoporous. However, the mesoporous structure decreased with the increase of the molar ratio of titanium and vanadium.
Keywords/Search Tags:Mesoporous molecular sieve, crystalline mesoporous molecularsieves, high content metal, heteroatom molecular sieve, benzene hydroxylation, phenol hydroxylation, selective oxidation cyclohexane
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