| 题名 | 磁性复合载体的制备及金属活性组分Pd的纳米化负载研究 |
| 作者 | 郎宇琪 |
| 学位类别 | 博士 |
| 答辩日期 | 2009-06-09 |
| 授予单位 | 中国科学院过程工程研究所 |
| 授予地点 | 过程工程研究所 |
| 导师 | 刘会洲 |
| 关键词 | 磁性载体 制备 钯 纳米催化剂 微乳液法 |
| 其他题名 | Preparation of Magnetic Composites Support and Study on Supported Palladium Nanoparticles Catalyst |
| 学位专业 | 化学工艺 |
| 中文摘要 | 纳米催化剂具有独特的结构和表面特性，催化活性和选择性远高于传统催化剂，但在实际应用中由于颗粒细小，热稳定性差，且反应结束后催化剂分离回收困难，限制了其在催化领域的应用。磁性载体具有良好的分离回收特性，可利用其超顺磁性的优点来解决上述问题，使制备的磁性催化剂既有纳米贵金属优良的催化活性，又能通过外加磁场很容易实现催化剂的回收。但目前仍存在磁性纳米载体的比表面积有限，不易达到适用于高分散性纳米粒子的要求，特别是经过表面功能化后，粒子的形貌、尺寸均匀度、分散度难以控制。针对上述概况，本文系统研究了以W/O微乳液为纳米反应器的磁性SiO2、磁性γ-Al2O3载体制备，Pd金属组分负载及其在硝基苯加氢制苯胺催化体系中应用。 构建了微乳液体系稳定性的热力学模型，利用拟三元相图，对影响W/O微乳液相区的因素进行考察。结果表明采用TX-100作为表面活性剂时，当TX-100与正己醇质量比等于3：2，所形成的界面膜具有较高的稳定性，存在较大的W/O微乳液区域；随着温度的升高，W/O微乳液稳定区域呈下降的趋势；水相pH值改变对W/O微乳液相区影响不大，体系具有较好的pH稳定性；当水相为电解质溶液时，W/O微乳液区域随其浓度的增大而减小。 针对现有磁性SiO2载体比表面小的缺陷，将溶胶-凝胶法制备纳米SiO2的原料配比应用于W/O微乳体系，通过调控W/O微乳液的反应条件，合成了比表面积高、粒径分布均匀、高度分散的磁性SiO2载体。TEM、N2吸附表征说明制备的磁性SiO2载体具有较大的比表面积和规则介孔结构，BET测定比表面386.8 m2/g，BJH脱附累积孔容为1.38 cm3/g，远高于溶胶-凝胶法和传统微乳液法制备的磁性SiO2复合颗粒。VSM表征磁性SiO2载体具有超顺磁性，比饱和磁化强度达到20~30 emu/g。 在超顺磁性Fe3O4纳米粒子表面进行SiO2包覆和Al2O3金属氧化物层的可控沉积，制备磁性γ- Al2O3载体，并通过多种表征手段对磁性γ- Al2O3载体的粒径、形貌、结构、组成和磁性能等进行了表征。结果表明产物尺寸分布均匀，具有超顺磁性。通过溶剂热处理、W/O微乳液的反应条件的改变对磁性γ- Al2O3复合颗粒的孔结构进行了调控，制备了比表面积397.3m2/g，孔径分布8~15nm，孔容0.851 ml/g有序介孔磁性氧化铝，其比表面积、孔容和孔径都远大于传统的活性氧化铝。 采用先合成Pd纳米粒子再组装的技术，通过改变水/表面活性剂比值、Pd负载量，成功制备了平均粒径7~20nm均匀分布的Pd/磁性γ- Al2O3负载催化剂。利用硝基苯加氢制苯胺的催化反应对催化剂进行活性评价，确定适宜制备和反应条件。结果表明硝基苯加氢制苯胺反应对NB宏观表现为零级反应，在Pd负载量1%，磁性Fe3O4的添加量8%、催化剂焙烧时间4~6h，反应时间50min，反应温度50℃，反应压力0.5MPa，硝基苯的转化率和苯胺选择性均可达到100%。套用实验表明该催化剂具有较好的稳定性和寿命，催化剂具有超顺磁性，反应结束后可在外加磁场作用下与产物快速分离，实现催化剂回收和重复使用。 针对微乳法制备催化剂需要大量有机溶剂及合成步骤多的缺陷，在制备磁性SiO2复合颗粒的基础上，采用一步溶剂萃取法对颗粒表面进行改性，在用乙二醇为分散溶剂和PdCl62-还原剂，采用微波辅助制备Pd/磁性SiO2催化剂，通过不同升温速率和乙二醇溶液的pH值对Pd纳米颗粒粒径和表面分散均匀性进行控制，并对硝基苯加氢制苯胺催化活性及其稳定性的进行了考察，发现随着升温速率从4.2K•s-1升至7.6K•s-1时，Pd粒子大小分布均匀，Pd粒子平均粒径从5.8nm降至3.8nm。随着pH值从5.6升高到9.0时，Pd纳米粒子平均粒径从4.3nm降至3.2nm，粒径的标准偏差和相对偏差逐渐减小，表明Pd纳米粒子的均匀性越来越好。催化剂在硝基苯加氢制苯胺催化反应中表现出较高活性及选择性，催化剂活性随Pd粒子平均粒径的减小而明显增加。 |
| 英文摘要 | The nanocatalysts have the higher activity and selectivity than traditional catalysts because of their special physical and chemical properties. However, the difficulties of separation of nanocatalysts limit their application in the field of catalysis. Magnetic carriers display superparamagnetism, which means that the nanocatalysts can be removed and recycled from solution by applying an external magnetic field. But some major problems that can not be satisfied the conditions of high dispersion of nanoparticles still remain. It is difficult to control size distribution and morphology of magnetic nanoparticles, particularly those surface functionalized ones. To meet these challenges, in this paper, systematical study have been carried out on the preparation of magnetic sillica and γ- Al2O3 carrier by using W/O microemulsions as nanoreactor, palladium nanoparticles loading on carrier and application in nitrobenzene directly hydrogenating to aniline system. A thermodynamic model is developed to study the stability of the microemulsion, and the influences on the homogeneous region in W/O microemulsion are studied by utilizing the pseudo-triangle phase diagram. When using TX-100 as surfactant and the weight ratio of n(S)/m(CS) equals to 1.5，the interface between water and oil is the most stable and can form the largest W/O microemulsion homogeneous region. As the increase of temperature, the area of W/O microemulsion region decreases evidentily. The pH value of the water phase and the length of the carbon chain of the co-surfactant have less effect on the stability of the W/O microemulsion. With the increase of concentration of electrolyte solution as water phase, the area of W/O microemulsion homogeneous region decreased greatly. According to the problems of low surfaces area of magnetic nanoparticles, the new method that W/O mieroemulsion coupling with sol-gel proeess for the preparation of ordered mesoporous superparamagnetic silica nanocomposites was developed. With changing reaction conditions, the size controllable mono-dispersed spherical silica partieles with diameter of 100 nm were prepared. Through the detailed characterization with TEM, BET and VSM, it concluded that the carrier has large specific surface area of 386.8 m2/g and mesoporous structure. The specific surface area and specific volume are higher than that prepared by either sol-gel method or single W/O microemulsion. Magnetic silica carriers exhibit superparamagnetic behavior with zero coercivity and their saturation magnetization was 20~30 emu/g. By controlled hydrolysis of alumina alkoxide and ratio of water in the W/O microemulsion, Fe3O4 superparamagnetic nanoparticles were coated with a silica protection shell, and subsequent metal oxide shell to form magnetic γ-Al2O3 carriers with diameter of 100~200nm were prepared. The size, morphology, structure, composition and magnetic properties of magnetic γ-Al2O3 carriers were characterized by XRD, TEM, BET, and VSM, respectively. The magnetic composites exhibit superparamagnetic behavior with zero coercivity and remanence. Surface area of magnetic γ-Al2O3 carriers can reach up to 397.3m2/g, the pore diameter covers from 8 nm to 15 nm. The properties of specific area and pore structure are greater than that of the traditional Hactivated aluminaH. Magnetic γ-Al2O3 nanocomposites supported Pd catalysts were synthesized by the assembly of Pd nanopartiele prepared beforehand in W/O microemulsion. The average size of the Pd nanoparticles is 8~30 nm with a narrow size distribution. The size and dispersion of palladium nanoparticle on the magnetic carrier can been adjusted by changing the constitutes of microemulsion and preparing conditions such as reaction time, the concentration of palladium loading in catalyst.The catalytic behaviors of the obtained magnetic nanocatalysts were measured by the nitrobenzene hydrogenat to aniline. The results showed the conversion of nitrobenzene and selectivity of aniline could reach 100% under optimized reaction conditions, such as the catalyst calcined time of 4~6h, reaction time of 50 min, reaction temperature of 50min, reaction pressure of 0.5MPa, etc. The result showed that the hydrogenation rate was independent of the concentration of NB，but dependent on the partial pressure of hydrogen. The catalysts can maintain the high activity after 10 recycles and be easily separated by the magnetic field． To meet the problem of using the amouts of organic solvents in W/O microemulsion, the Pd/magnetic silica catalysts were prepared by microwave heating of ethyleneglycol solution of Palladium salt in high temperature. The magnetic silica nanocomposties prepared were functionalized with the organic groups of –NH2 using one-step extraction functionalization method first. The effects of pH values of ethylene glycol solution and heating rates of reaction system on the sizes and uniformity of Pd nanoparticles dispersed on magnetic silica were investigated. TEM showed that the average diameter of Pd nanopaticles decreased slightly from 4.3nm to 3.2 nm with the increase of pH value from 5.5 to 9.0 for Pd/magnetic silica. In addition, increasing pH values of ethylene glycol solution can improve the size uniformity and dispersion of Pd nanopaticles on carriers. The activity measurement of nitrobenzene hydrogenating to aniline showed that Pd/magnetic silica catalysts have high catalytic activity under higher heating rates and pH values. |
| 语种 | 中文 |
| 公开日期 | 2013-09-13 |
| 页码 | 159 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.ipe.ac.cn/handle/122111/1111]  |
| 专题 | 过程工程研究所_研究所（批量导入） |
| 推荐引用方式 GB/T 7714 | 郎宇琪. 磁性复合载体的制备及金属活性组分Pd的纳米化负载研究[D]. 过程工程研究所. 中国科学院过程工程研究所. 2009. |
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