钴咪唑骨架衍生钴—氮掺杂多孔碳的合成及其在串联催化中的应用

发布时间：2019-03-10 18:10

【摘要】：金属-有机骨架(MOFs)材料是一类新型的无机-有机多孔晶态材料,其由金属原子/簇及有机配体通过配位键所组成。金属离子、配体及整体结构的多变性极大的提升了可调节性,配合其本身具有的高比表面积等特性,MOFs在许多方面都已经展现了潜在的应用,如气体吸附与分离、质子传导、药物输运、多相催化等。同时,MOFs的周期性结构使得其结构中不同原子的高度有序的排列,使得其可以作为良好的模板,通过高温热解方式来制备均匀掺杂的多孔碳材料。在惰性气氛下,热解的过程中虽然MOFs原本的结构遭到破坏,但其比表面积与孔洞仍可部分继承,从而得到具有高比表面积的多孔碳基复合材料,进一步的拓展了 MOFs的应用范围。芳香族和脂肪族的各种胺类在工业上有着十分广泛的应用。通常,其合成可通过相对应的硝基化合物加氢制备。为防止氢化过程中对其他可还原官能团产生影响,反应的选择性十分重要。然而,选择性氢化目前仍然主要依赖于高价的贵金属催化剂,使用廉价过渡金属的催化剂来替代贵金属是非常迫切的需求。同时,为了提高反应效率,以原位生成的氢代替传统使用的低溶解性的氢气是一个很好的思路。这些原位生成的氢能更好的与反应底物进行接触,从而提高反应效率。而氢含量高达19.6 wt%且具有良好溶解性的氨硼烷便是极好的选择,也即,将氨硼烷的脱氢与硝基化合物的氢化构成串联反应。我们以一种经典的MOF,沸石类型的钴咪唑骨架材料ZIF-67为模板和前体,通过热解制备了具有规则形貌的Co-CoO@N掺杂多孔碳复合催化剂。各项表征显示,表面被部分氧化为CoO的Co结晶纳米颗粒均匀地分布在N掺杂的多孔碳中。研究结果表明,所制备的MOF衍生催化剂在室温下即可高效催化氨硼烷脱氢及硝基化合物加氢这一串联反应进行,并且该催化剂可以多次重复循环使用。与使用1 bar的氢气时对比,该串联反应的效率要高出数个数量级。此外,该催化剂还可选择性地将含有不同取代基团的各种芳香族及脂肪族硝基化合物转化为对应的胺类化合物,反应在数小时即可完成,且转化率和产率最高可达100%。同时,对于含有其他还原性基团的底物(包括腈类、醛类及酮类),此催化剂均能保证其中的还原性官能团不受影响。
[Abstract]:Metal-organic skeleton (MOFs) materials are a new kind of inorganic-organic porous crystalline materials, which are composed of metal atoms / clusters and organic ligands through coordination bonds. The variability of metal ions, ligands and whole structures greatly improves the modulability. In combination with its high specific surface area, MOFs has shown potential applications in many fields, such as gas adsorption and separation, proton conduction, and so on. Drug transport, heterogeneous catalysis, etc. At the same time, the periodic structure of MOFs makes the highly ordered arrangement of different atoms in its structure, so it can be used as a good template for the preparation of uniformly doped porous carbon materials by pyrolysis at high temperature. In inert atmosphere, although the original structure of MOFs is destroyed during pyrolysis, its specific surface area and pores can be partially inherited, thus the porous carbon matrix composites with high specific surface area can be obtained, which further expands the application range of MOFs. Aromatic and aliphatic amines are widely used in industry. In general, its synthesis can be prepared by the corresponding nitro compound hydrogenation. In order to prevent the effect of hydrogenation on other reducible functional groups, the selectivity of the reaction is very important. However, selective hydrogenation is still mainly dependent on high-priced noble metal catalysts, and the use of cheap transition metal catalysts to replace precious metals is a very urgent need. At the same time, in order to improve the reaction efficiency, it is a good idea to replace the traditional low-solubility hydrogen with in-situ hydrogen. These in-situ hydrogen can better contact with the reaction substrate and thus improve the reaction efficiency. The ammonia borane with high hydrogen content as high as 19.6 wt% and good solubility is an excellent choice, that is, the dehydrogenation of ammonia borane and the hydrogenation of nitro compounds constitute a series reaction. Co-CoO@N doped porous carbon composite catalyst with regular morphology was prepared by pyrolysis using a classical MOF, zeolite type cobalt imidazole framework material ZIF-67 as template and precursor. The results show that the crystalline Co nanoparticles partially oxidized to CoO distribute uniformly in the N-doped porous carbon. The results show that the prepared MOF derivative catalyst can efficiently catalyze the series reaction of ammonia borane dehydrogenation and nitro compound hydrogenation at room temperature, and the catalyst can be reused for many times. Compared with 1 bar hydrogen, the efficiency of the series reaction is several orders of magnitude higher. In addition, the catalyst can selectively convert aromatic and aliphatic nitro compounds containing different substituted groups into corresponding amine compounds. The reaction can be completed in a few hours, and the conversion and yield can reach up to 100%. At the same time, for the substrates containing other reducing groups (including nitriles, aldehydes and ketones), the catalysts can ensure that the reducible functional groups are not affected.
【学位授予单位】：中国科学技术大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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