掺氮碳纳米管的制备及其催化硝基化合物加氢性能研究

发布时间：2018-05-13 02:37

  本文选题：掺氮碳纳米管 + 非金属催化剂　； 参考：《湘潭大学》2017年硕士论文

【摘要】：加氢反应的活性组分一般为金属,使用最广泛的催化剂是负载型贵金属催化剂,但由于贵金属的价格高,许多学者开始研究低成本的铜、镍等非贵金属负载型催化剂用于加氢反应。碳纳米管拥有良好的导电性,导热性,稳定性和高机械强度,是一种良好的催化剂载体,而杂原子掺杂的碳纳米管可以作为一种非金属催化剂催化氧还原反应,为杂原子掺杂碳纳米管应用在催化加氢反应中提供了新的思路。本工作制备了一类非金属掺氮碳纳米管催化剂,考察了不同催化剂对硝基化合物加氢反应的催化性能,并对这些催化剂进行表征,分析催化剂的“构-效”关系,同时优化了反应条件。本工作分别通过CVD法和后处理掺杂法两种方法制备掺氮碳纳米管,并对两种不同方法制备的氮掺杂碳纳米管的微观结构进行对比,发现CVD法制备的掺氮碳纳米管呈竹节状,在进行了探针反应后,发现CVD法合成的掺氮碳纳米管对加氢反应没有活性,所以本工作选用后处理掺杂法制备的掺氮碳纳米管用于加氢反应的研究。探讨了掺氮碳纳米管对1,5二硝基萘,硝基萘以及硝基苯加氢的催化性能,1,5二硝基萘在掺氮碳纳米管的催化作用下可以加氢生成1,5二氨基萘,但是选择性很低;掺氮碳纳米管在硝基萘加氢反应中同样表现出了一定的加氢活性,产物萘胺的选择性偏低,掺氮碳纳米管催化硝基苯加氢,产物苯胺的选择性可达90%以上,通过比较分析确定最优的催化剂为800℃下后处理掺杂制备的m-ONCNTs-800掺氮碳纳米管。本工作对掺氮碳纳米管催化硝基苯加氢反应进行了深入的研究,使用m-ON CNTs-800催化剂,优化了硝基苯加氢的反应条件,在170℃下,硝基苯用量1g,催化剂用量为0.1g,乙醇20ml,氢压4 MPa,反应时间8h时,硝基苯转化率为59.74%,选择性可达到91.48%。通过设计实验与表征分析排除了掺氮碳纳米管中残留的金属对催化剂加氢活性的影响,确定了掺氮碳纳米管催化加氢是非金属催化,通过分析得到在硝基苯加氢反应四方氮与吡啶型氮可能是影响催化性能的活性中心。本工作采用MS软件对掺氮碳纳米管进行模拟计算,发现氮原子的掺杂会改变碳纳米管的LUMO和HOMO轨道,掺杂的氮原子上具有更高的电负性,周围的碳原子都带有明显的正电荷,说明氮原子掺杂的碳纳米管在杂质氮原子附近位置的化学活性较高。计算结果表明氮掺杂的碳纳米管和H2之间的吸附为化学吸附,未掺杂的碳纳米管与H2分子较难生成化学键。
[Abstract]:The active component of hydrogenation reaction is usually metal. The most widely used catalyst is supported noble metal catalyst. However, due to the high price of precious metal, many scholars have begun to study low cost copper. Nickel and other non-noble metal supported catalysts are used for hydrogenation. Carbon nanotubes (CNTs) have good electrical conductivity, thermal conductivity, stability and high mechanical strength, so they are a good catalyst carrier, while hetero-atom-doped CNTs can be used as a non-metallic catalyst to catalyze oxygen reduction. It provides a new idea for the application of hetero-atom doped carbon nanotubes in catalytic hydrogenation. In this work, a class of non-metallic nitrogen-doped carbon nanotube catalysts were prepared. The catalytic properties of different catalysts for hydrogenation of nitro compounds were investigated, and these catalysts were characterized to analyze the "structure-activity" relationship of the catalysts. At the same time, the reaction conditions were optimized. In this work, nitrogen-doped carbon nanotubes (NCNTs) were prepared by CVD method and post-treatment doping method, respectively. The microstructure of nitrogen-doped CNTs prepared by two different methods was compared. It was found that the nitrogen-doped CNTs prepared by CVD method were bamboo-shaped. After the probe reaction, it was found that the nitrogen-doped carbon nanotubes synthesized by CVD method had no activity for hydrogenation, so the nitrogen-doped carbon nanotubes prepared by the post-treatment method were used in the study of hydrogenation reaction. The catalytic properties of nitrogen-doped carbon nanotubes (CNTs) for the hydrogenation of 1n 5 dinitronaphthalene, nitrone naphthalene and nitrobenzene were discussed. The hydrogenation of 1 nitro 5 dinitronaphthalene with nitrogen-doped carbon nanotubes can produce 1 N 5 diaminaphthalene, but the selectivity is very low. The nitrogen-doped carbon nanotubes also showed a certain hydrogenation activity in the hydrogenation of nitronaphthalene. The selectivity of the product naphthylamine was low, and the selectivity of aniline could reach more than 90% in the hydrogenation of nitrobenzene catalyzed by nitrogen-doped carbon nanotubes. Through comparative analysis, the optimum catalyst is the m-ONCNTs-800 nitrogen-doped carbon nanotubes doped at 800 鈩，

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