【作者】 刘振兴；

【导师】 李保山；

【作者基本信息】 北京化工大学 ， 化学工程与技术， 2011， 博士

【摘要】 杂多酸是由两种或两种以上不同含氧酸经缩合脱水而形成的多聚含氧酸。由于其优异的酸性及氧化还原性而被广泛地应用于各种酸催化及催化氧化反应体系中。但杂多酸存在比表面积小、热稳定性差、重复使用性低等缺点，使得它在工业上的应用受到了一定的限制。因此，将杂多酸组装到合适的载体上，对提高其比表面积、催化活性及重复使用性具有重要的意义。蒙脱土作为一种层间具有可交换阳离子的层状硅酸盐粘土矿物，通过离子交换、插层柱撑等方法，可在其层间引入大量的有机、无机离子，形成多孔复合功能材料。已发表的很多文献都是将杂多酸负载于蒙脱土原土或改性蒙脱土载体上，而杂多酸插层蒙脱土复合催化材料的研究鲜见文献报道。因此，将杂多酸组装到柱撑蒙脱土材料中，使其牢固地附着于蒙脱土的层间骨架结构中，有效避免杂多酸在催化反应过程的流失，可以有效提升催化剂的性能，具有重要的学术价值及实际应用前景。本文采用离子交换、溶胶凝胶、原位合成、分子自组装等方法，将磷钨杂多酸有效引入蒙脱土层间，用X射线粉末衍射（XRD）、X射线荧光分析（XRF）、傅利叶变换红外光谱（FT-IR）、热重-差热分析（TG-DTA）、氮气等温吸附-脱附（BET）、扫描电镜（SEM）和透射电镜（TEM）等分析测试手段，对杂多酸插层蒙脱土复合材料的结构、稳定性等进行了表征。研究了不同表面活性剂、不同杂多酸含量以及不同杂原子取代的缺位杂多酸对柱撑蒙脱土复合材料结构的影响，探讨了杂多酸插层蒙脱土复合材料的形成机理，考察了复合材料对模拟油、FCC柴油氧化脱硫的催化性能。取得了以下研究成果。1．用十六烷基三甲基溴化铵作为合成柱撑蒙脱土的层间模板剂，制备了不同含量的磷钨酸插层蒙脱土复合材料，并用浸渍法制备了相同磷钨酸含量的负载型磷钨酸/蒙脱土复合材料。结果表明，在磷钨酸插层蒙脱土复合材料中，磷钨酸被引入了柱撑蒙脱土层间骨架结构，并且保留了其原有的Keggin型结构，其氧化脱硫催化活性远远高于负载型磷钨酸/蒙脱土复合材料。当反应温度为60oC，反应时间为120min，H2O2/S摩尔比为3时，0.15g催化剂能将25mL模拟油中的硫含量由500ppm的降低到7.1ppm，硫的脱除率为98.6%。2．以不同分子链长和带有不同官能团的表面活性剂作为合成柱撑蒙脱土的层间模板剂，通过离子交换法和溶胶-凝胶法，将磷钨酸成功地引入柱撑蒙脱土的层间骨架结构，制备了一系列磷钨酸插层蒙脱土复合材料。研究发现复合材料的层间距和比表面积都随着模板剂分子链长的增加而增加，模板剂的有机官能团种类对磷钨酸插层蒙脱土杂化材料的比表面积、孔容、孔分布也都有很大的影响。当模板剂中带有苄基时，形成的磷钨酸插层蒙脱土复合材料的孔容高达1.29cm3g-1，孔径为9.0nm，但较大的孔径不利于杂多酸插层蒙脱土复合材料的稳定。催化研究结果表明，虽然用十六烷基三甲基溴化铵作为合成柱撑蒙脱土的层间模板剂时，形成的材料的脱硫催化活性没有用含有苄基的模板剂形成的材料高，但前者具有更好的稳定性，重复使用性好。3．在酸性条件下制备了单缺位磷钨酸和过渡金属杂原子修饰的缺位磷钨酸，并通过溶胶-凝胶法将这些缺位磷钨酸插层入了柱撑蒙脱土的层间骨架结构中，形成了介孔缺位磷钨酸插层蒙脱土复合材料。缺位磷钨酸的引入并没有破坏蒙脱土的片层结构，并且这种复合催化材料具有均一的孔径，但杂原子缺位磷钨酸对柱撑蒙脱土材料的形貌影响较大。模拟油的催化氧化脱硫实验结果表明，单缺位磷钨酸插层蒙脱土材料的催化效果比磷钨酸插层蒙脱土材料的好，几乎能够将模拟油中的DBT完全氧化脱除。但杂原子缺位磷钨酸插层蒙脱土材料的催化活性却有所降低，这是由于缺位磷钨酸中杂原子的引入破坏了杂多酸的质子酸结构，从而导致催化效果不理想。4．采用原位合成法，在强酸性介质中制备了不同磷钨酸含量的磷钨酸插层蒙脱土复合材料，并用多种分析手段对复合材料进行了表征。结果表明：原位磷钨酸插层蒙脱土复合材料中，磷源和钨源引入了柱撑蒙脱土层间骨架结构中，并原位生成了磷钨酸。在引入高含量磷钨酸的情况下(25wt.%)，蒙脱土的片层结构仍能得到了很好的保留。该催化剂对模拟油具有较好的氧化脱硫催化活性，并且其催化活性随着催化剂中原位引入的磷源和钨源含量的增加而提高。但过量磷钨酸在蒙脱土层间的原位生成，对材料的结构和催化活性都有一定的不利影响。当反应温度为60oC，反应时间为120min，H2O2/S摩尔比为3时，0.15g催化剂能将25mL模拟油中的硫含量由500ppm的降低到18.5ppm，脱硫率为96.3％。5．探讨了磷钨酸插层蒙脱土复合材料的合成机理。认为此类磷钨酸插层蒙脱土复合材料是通过层间离子交换和分子自组装技术将杂多酸引入柱撑蒙脱土层间骨架结构中的。首先，阳离子模板剂通过离子交换技术与蒙脱土层间的阳离子进行交换，形成有机蒙脱土。然后，通过分子自组装技术将磷钨酸引入蒙脱土层间。最后，在蒙脱土层间分子与引入的硅柱撑剂的相互作用过程中，杂多酸和硅羟基相互键合形成硅柱撑蒙脱土骨架的一部分。6．探讨了复合材料的催化氧化脱硫机理。在油品的催化氧化脱硫过程中，磷钨酸插层蒙脱土复合材料骨架结构中的磷钨酸能够接受双氧水中的活性氧，并形成一个中间态的杂多过氧化物，而硅柱撑蒙脱土材料则能将这种杂多过氧化物转移到油品中的含硫底物上，使氧化反应顺利进行。模拟油催化氧化前后的GC-MS测定结果表明，油品中的含硫化合物被氧化成极性较强的砜类物质，最终通过极性溶剂乙腈萃取，从而达到脱硫的目的。而磷钨酸插层蒙脱土复合材料中的磷钨酸由于已经插层入柱撑蒙脱土的层间骨架结构中，因而具有较高的稳定性。更多还原

【Abstract】 Heteropoly acid (HPA) is formed by two or more different oxy-acidthrough condensation. Due to its excellent acidity and redox property, it hasbeen widely applied in all sorts of catalytic oxidation and acid catalyzedreaction system. However, HPA suffers from some shortcomings, such as thesmall surface area, low thermal stability and the undesirable reusability.Thesedrawbacks greatly limit their applications in catalytic processes. Thus, it hasgreat significant to load HPA onto appropriate carrier to improve its specificsurface area, catalytic activity and reusability. As a kind of layered silicateclay mineral with interlayer cation exchange property, montmorillonite (MMT)can be introduced large quantities of organic and inorganic ions in theinterlayer, forming porous composite functional materials by ion exchange,intercalation, and pillaring method etc. Former researchers did a lot of workon loading heteropoly acid on MMT or modified MMT, but there are fewreports on heteropoly acid intercalated MMT catalytic composite in the literature. Therefore, assembling the HPA into the silica pillared MMTmaterial can make the HPA firmly stick to the interlayer framework of MMT.It will reduce the loss of HPA in the catalytic reaction and improve thecatalytic performance of the catalyst, which has important academic value andpractical applicationThis paper applied ion exchange, sol-gel, in situ synthesis, and molecularself-assembly methods etc, effectively introduced phosphotungstic acid (HPW)into the interlayer of MMT. Using X-ray powder diffraction (XRD), X-rayfluorescence analysis (XRF), fourier transform infrared spectroscopy (FT-IR),thermogravimetry-differential thermal analysis (TG-DTA), nitrogenisothermal adsorption-desorption (BET), scanning electron microscopy (SEM),transmission electron microscope (TEM), and many other kinds of testmethods characterized the structure, stability of the HPW intercalated MMTcomposite. This paper studied the effect of the different surfactant, differentcontent of HPW and different heteroatoms vacancy phosphotungstic acid tothe interlayer structure, discussed the formation mechanism of the compositematerials, examined the catalytic desulfurization performance of the catalyticmaterials to the model oil and the catalytic cracking FCC diesel oil. The mainresearch work and achievements are as follows.1. Using hexadecyl three methyl ammonium bromide (CTAB) as theinterlayer templates of the silica pillared MMT, different content ofphosphotungstic heteropoly acid intercalated MMT composites (HPW-SPC) were prepared. HPW/MMT samples with the same phosphotungstic acidcontent were also prepared using the imprepnation method. Results showedthat HPW was intercalated into the interlayer framework of the silica pillaredMMT composites, and its original Keggin structure retained. Oxidationdesulphurization experiment results showed that the HPW-SPC samplesexhibited far higher catalytic oxidative activity than the impregnation samples.When the reaction temperature is60oC, H2O2/S=3:1,0.15g catalyst canreduce the sulfur content in25mL of model oil from500ppm to7.1ppm in120min, with sulfur removal of98.6%.2. A series of phosphotungstic acid intercalated MMT desulfurizationcomposites were prepared using surfactants with different molecular lengthand different functional groups as silica pillared MMT interlayer template.HPW was successfully introduced into the interlayer framework of silicapillared MMT composites by ion exchange and sol-gel method. The interlayerspacing and specific surface area of the composite catalytic materials enlargedwith the increase of the carbon length of the templates. The organic functionalgroup has a great influence on the specific surface area, pore distribution andpore volume of the phosphotungstic acid intercalated MMT composite. Whena template with benzyl was introduced into the interlayer of the MMT clay, theformed MMT hybrid material has a large pore volume of1.29cm3.g-1andlager pore size (9.0nm). However, the large pore size affected the stability ofHPW-SPC composite. Catalytic experimental results showed that, although the resulting material prepared using CTAB as the silica pillared MMTtemplate did not exhibit excellent catalytic desulphurization performance asthe materials formed by the template with benzene ring, it possesses a highstability and good reusability.3. The mono-lacunary phosphotungstic acid and transiton metal modifiedlacunary phosphotungstic acid were synthesized under acidic condition. Theselacunary phosphotungstic heteropoly acids were intercalated into the interlayerframework of the silica pillared MMT by sol-gel method and formedmesoporous lacunary phosphotungstic acid intercalated MMT composites(MPW11-SPC). The introduction of the lacunary phosphotungstic acid did notdestroy the lamellar structure of MMT and these composite materials possessuniform pore size. However, the transiton metal modified lacunaryphosphotungstic acid has a strong influence to the morphology of silicapillared MMT composite. The results of the catalytic oxidation desulfurizationshowed that, the mono-lacunary intercalated MMT composites showed bettercatalytic performance than the phosphotungstic acid intercalated MMTcomposites, which can nearly completely catalytic oxidize DBT into thecorresponding sulfone. But, the catalytic performance of the transiton metalmodified lacunary phosphotungstic acid intercalated MMT compositesreduced. This is because the Br nsted acid structure of the heteropoly acidstructure was damaged with the introduction of the impurity atoms, thus thecatalytic performance is not so ideal. 4. In strong acidic medium, different content of phosphotungstic acidintercalated mesoporous MMT composites were prepared using in situsynthesis method. The composites were characterized by various analysismethods. The results showed that tungsten source and phosphorus source weresuccessfully intercalated into the interlayer framework of the silica pillaredMMT, and in-situ synthesized phosphotungstic acid. When high content(25wt.%) of HPW was introduced into the framework of the MMT compositeby in situ synthesis method, the MMT lamellar structure was also wellpreserved. The catalyst showed a good catalytic performance in oxidizationdesulfurization of DBT in the model oil, and its catalytic performanceimproved with the increase of the content of tungsten source and phosphorussource. But the formation of excessive amounts of HPW has an adverse effectto the structure and catalytic activity of the material. When the reactiontemperature is60oC, H2O2/S=3,0.15g catalyst can reduce the sulfur contentin25ml model oil from500ppm to18.5ppm in120min, with thedesulphurization removal of96.3%.5. Discussed the synthesis mechanism of the HPW-SPC materials. TheHPW-SPC materials were synthesized through the interlayer ion exchange andmolecular self-assembly technology with HPW anion introduced into theframework of the pillared MMT clay. Firstly, the cationic template wasintroduced into the interlayer of the MMT through the ion exchangetechnology, forming the organic MMT. Then, through molecular self-assembly technology the HPW anion was attracted into the interlayer of the MMT.Finally, during the interaction process of the introduced silicon source and themolecules in the interlayers of MMT, phosphotungstic acid will bond with thesilicon hydroxyl forming a part of the framework of the silica pillared MMTcomposite.6. Explored the catalytic oxidation desulfurization mechanism. During theoxidation desulfurizaion process, HPW in the interlayer framework of thepillared MMT composite can accept the activce oxygen free radicals from thehydrogen peroxide and form a middle state oxoperoxo species, while the silicapillared MMT materials will transfer the oxoperoxo species to thesulfur-containing substrates, make the oxoperoxo species contact with thesulfur-containing compound, leading the oxidation reactions proceed smoothly.The GC-MS results of the model oil before and after catalytic oxidationreaction showed that the sulfur-containing compounds were oxidized intosulfone with relatively strong polarity, which can be extracted by theacetonitrile solvent, so as to achieve the purpose of desulfurization. And,because the HPW in the HPW-SPC materials was intercalated into theinterlayer framework of the silica pillared MMT, it can be constantly reuse andshow good reusability.更多还原