多孔锆基氧化物材料的制备及性能研究

发布时间：2018-01-19 15:03

本文关键词： 锆基氧化物高比表面积热稳定性氧化乙苯脱氢　出处：《太原理工大学》2017年博士论文　论文类型：学位论文

【摘要】：根据国际纯粹和应用化学联合会对孔材料的定义,多孔材料可按其孔径的大小划分成微孔材料(孔径2nm)、中孔或介孔材料(2nm孔径50nm)以及大孔材料(孔径50nm)三类。美国学者Dubinin又提出了一种孔径介于1-2nm之间的超微孔材料。这种材料的孔径尺寸弥补了在该区间对分子择形有特殊需求的反应,在微孔和介孔材料之间架起了承上启下的桥梁,具有广阔的应用前景。金属氧化物氧化锆作为一种多功能兼具酸性和碱性的催化剂载体,常通过硫酸化、磷酸化或钨酸化成为一种强的固体酸。硫化氧化锆虽然酸性较强,但比表面较小。通常借助具有高比表面的硅基有序中孔材料负载氧化锆应用于催化裂解、烷烃异构化等反应,但是中孔材料的表面性能不利于四方相氧化锆的生成,而四方相氧化锆(t-Zr O_2)是SO42-/Zr O_2的基础。因此,通过新的技术路线或已有制备工艺的改进,合成具有高热稳定性和高比表面的中孔-微孔多晶体结构的四方相氧化锆基材料,具有极大的挑战性和十分重要的意义。国内外学者对于孔材料的合成已提出了诸多成功的制备方案,并且有些技术可以达到根据实际应用需求而定向、精准合成所需类型的多孔材料。其中应用最多的是软模板法制备孔材料,该方法又称模板剂或结构导向剂方法,其特点是充分利用模板剂在合成过程中所特有的模板剂效应,去制备、调控材料的孔结构。通常认为,模板剂在所合成的液相体系中所形成的胶束的尺寸大小决定所合成材料孔径的尺寸范围,模板剂的种类和制备条件影响着分子筛的水热稳定性和多级孔材料孔径的大小及其分布。因此,筛选性能优越、环境友好、价廉易得的模板剂,并进一步优化合成工艺和创新合成路线已成为广大科研人员积极探索的热点和难点。本课题采用溶剂挥发诱导自组装的方法,以双链季铵盐阳离子表面活性剂作为软模板(结构导向剂),通过改变表面活性剂中碳链的长度(双八烷基二甲基氯化铵、双十二烷基二甲基氯化铵、双十八烷基二甲基氯化铵)制备得到了孔结构可控的氧化锆材料,且合成过程中无需额外添加酸碱等助剂,而是通过前驱体的自身水解产生的酸碱性达到自我调节从而获得相应结构的多孔材料。以溴化十六烷基吡啶为模板剂,氧氯化锆或丙醇锆为锆源前驱体,通过溶剂挥发诱导自组装法和固液技术相结合的新策略制备出具有高比表面积的中微孔级纳米晶体氧化锆材料。孔结构表征结果显示,400℃焙烧脱模板后,其具有高的比表面积414m2/g;即使在700℃热处理后,仍然具有较高的比表面积223m2/g。而通过单一溶剂挥发法合成的氧化锆材料经相应温度热处理后,孔结构基本坍塌,比表面积小于50m2/g。在成功制备出微孔氧化锆的基础上,且不额外添加任何酸、碱等助剂的情况下将金属铝盐引入,得到了具有超微孔结构、高热稳定性以及高水热稳定性的氧化铝-氧化锆复合材料。合成得到的Al_2O_3-Zr O_2复合材料具有蠕虫状孔道结构,Al的含量能够在较大范围内进行调节,且该材料具有较高的比表面积和均一的孔径分布。Al元素的引入使得该微孔材料具有稳定的四方相结构,致使含有微孔结构的此复合材料的热稳定性远大于相应氧化锆材料。当Al/Zr摩尔比为1.0时,该复合材料在800℃热处理后仍具有微孔结构,且比表面积高达216 m2/g,显示出高的热稳定性。以制备的Al_2O_3-ZrO_2复合材料为载体,采用浸渍法制备含钴催化剂并将其应用于二氧化碳气氛下氧化乙苯脱氢反应。研究发现催化剂用量为300mg,CO_2气体流量为20m L/min,乙苯流量为0.3m L/h,550℃下连续反应10h时,随着Al/Zr摩尔比的不断增加,其乙苯转化率不断增加;当Al/Zr摩尔比为0.7时,转化率达到最高值58.71%,其催化活性达到最大,且苯乙烯选择性不低于96%;继续增加Al/Zr摩尔比到1.0,乙苯转化率为57.73%,苯乙烯选择性不低于96%,催化活性基本维持不变。作为对比,在相同的反应条件下,对采用相同制备方案得到的Co/Al_2O_3和Co/Zr O_2催化剂进行同样的催化性能测试,结果显示活性钴原子负载于Al_2O_3-Zr O_2复合材料所表现出的催化活性远高于单一氧化锆或氧化铝孔材料为载体的相应催化剂。并且在N2气氛下,其Al_2O_3-Zr O_2复合材料仍然显示了较好的催化活性,是目前锆基催化剂相关研究中鲜有报道的。鉴于此,运用此制备方案又成功制备了氧化镁-氧化锆复合材料。孔结构表征显示该产物具有较大的比表面积以及集中的孔分布,600℃热处理后仍然为纯四方相。在豆油和甲醇的酯交换催化反应中,以所制备的镁锆复合材料为催化剂进行系统考察,结果表明当Mg/Zr摩尔比为0.5时,经过150℃反应6h后,催化剂对豆油的转化率可达到99%以上,显示出极高的酯交换反应活性。表明此复合材料将会在该催化领域具有较高的应用价值。该制备方案的成功运用将为今后规模化制备孔结构可调控的高比表面积、环保易得、高热稳定性的多级孔锆基复合材料提供理论依据和技术指导。
[Abstract]:According to the IUPAC definition of mesoporous materials, porous materials into microporous materials according to their pore size (2nm in diameter), divided mesoporous or mesoporous materials (2nm 50nm in diameter) and macroporous materials (50nm in diameter) three. The American scholar Dubinin proposed supermicropore between pore size between 1-2nm. The pore size of this material made in the interval has special requirements on the molecular shape selective reactions between microporous and mesoporous materials built connecting bridge, and has broad application prospects. The metal oxide zirconium oxide as a multifunctional catalyst carrier in both acidic and alkaline, often through sulfation, phosphorylation or acidification of tungsten become a strong solid acid. Although the sulfated zirconia strong acid, but smaller specific surface. Usually by silicon substrate with high surface area mesoporous materials supported zirconium oxide used in Catalytic cracking, isomerization reaction, but the surface properties of mesoporous materials is not conducive to the formation of tetragonal zirconia, and tetragonal zirconia (t-Zr O_2) is the foundation of SO42-/Zr O_2. Therefore, the improved preparation of new or existing technical route system, synthesis of mesoporous - high thermal stability and high the surface of the microporous crystal structure of tetragonal zirconium based material phase oxidation, is of great challenge and great significance. Domestic and foreign scholars for the synthesis of mesoporous materials has made many successful preparation scheme, and some technology can be achieved according to the actual application requirements and orientation precision required for the synthesis of porous material type. Which is the most widely used in preparing porous material by soft template method, this method is also called template or structure directing agent method, which is characterized by the template effect and make full use of the unique template in the synthesis process, to By controlling the pore structure of the material. Generally, the size range of size determines the size of the template in the synthesis of liquid phase system of micelles formed by the synthetic aperture material, preparation conditions of template agent and system affects the hydrothermal stability of zeolite and hierarchical porous materials hole size and distribution of diameter. Therefore, screening of superior performance, environment friendly, template agent is cheap, and further optimize the synthetic route and innovation has become a hot and difficult scientific research personnel to actively explore the method in this paper. By evaporation induced self-assembly, as soft template with double chain quaternary ammonium cationic surfactants (structure oriented agent), by changing the surface active agent in the carbon chain length (double eight alkyl two methyl ammonium chloride, didodecyl dimethyl ammonium chloride two, double eighteen alkyl two methyl ammonium chloride) were prepared by controlled pore structure The zirconia material, and the synthesis process without addition of acid and other additives, but pH produced by precursor hydrolysis to regulate themselves so as to obtain porous material corresponding to the structure. In sixteen alkyl pyridine bromide as template, zirconium or zirconium propoxide as zirconium precursor, were induced by the new the strategy of self-assembly and solid technology combined with the preparation of high specific surface area of the porous nano crystal zirconia material by solvent evaporation. The pore structure characterization results show that 400 degrees off the template after roasting, which has a high specific surface area of 414m2 /g; even after heat treatment at 700 DEG C, still has a high the specific surface area of 223m2/g. and the single zirconia materials synthesized by solvent evaporation method with corresponding temperature after heat treatment, the basic structure of hole collapse, a surface area of less than 50m2/g. in the prepared porous zirconia based on, and not Any additional acid, alkali and other additives under the condition of the metal aluminum salt has been introduced, with super microporous structure, high thermal stability and high hydrothermal stability of alumina zirconia composite materials. Al_2O_3-Zr O_2 composites were synthesized with wormlike pore structure, the content of Al can be adjusted in a large range, and the the material has high specific surface areas and uniform pore size distribution of.Al element into the microporous material with stable tetragonal structure, the thermal stability of the composite material containing porous structure is far greater than the corresponding zirconia material. When the Al/Zr molar ratio is 1, the composite material has porous structure in 800 degree heat after the treatment, and the specific surface area of up to 216 m2/g, showed high thermal stability. Al_2O_3-ZrO_2 composites were prepared by the carrier, was prepared by impregnation and the cobalt catalyst For the oxidative dehydrogenation of ethylbenzene under carbon dioxide atmosphere. The study found that the amount of catalyst is 300mg, CO_2 gas flow rate of 20m L/min, 0.3m L/h 10h, ethylbenzene flow, continuous reaction at the temperature of 550 DEG C, with the increase of the molar ratio of Al/Zr, the conversion of ethylbenzene increases; when the Al/ Zr molar ratio was 0.7, the conversion rate reached the highest value 58.71%, the catalytic activity and selectivity of styrene reached a maximum of not less than 96%; with the increase of Al/Zr molar ratio to 1, the ethylbenzene conversion rate was 57.73%, the selectivity of styrene is not less than 96%, the catalytic activity remained unchanged. In contrast, under the same reaction conditions, catalytic performance test of the same with the same preparation plan Co/Al_2O_3 and Co/Zr O_2 results showed that the activity of catalyst, catalytic activity of cobalt atom load in Al_2O_3-Zr O_2 composites showed much higher than that of single zirconia or alumina material The material for the corresponding catalyst carrier. And in the atmosphere of N2, the Al_2O_3-Zr O_2 composites still showed good catalytic activity, is currently little research in zirconium base catalyst are reported. In view of this, Magnesium Oxide - zirconia composite materials were prepared by using the preparation and characterization of pore structure were successfully. The result shows have a larger surface area and pore size distribution of 600 DEG C after heat treatment is still a pure tetragonal phase. In soybean oil and methanol transesterification reaction, the magnesium zirconium composite material prepared by the catalysts were investigated, the results show when the Mg/Zr molar ratio is 0.5, after 150 DEG C 6H after the transformation of catalyst oil ratio can reach more than 99%, showing a very high transesterification activity. This indicates that the application of composite material will have a higher value in the field of catalysis. The preparation of the successful application will be In the future, large-scale production of porous structure with adjustable surface area, environmental protection and high thermal stability will provide theoretical basis and technical guidance for multistage Kong Gaoji composite materials.

【学位授予单位】：太原理工大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ134.12;TB383.4

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