多孔碳氮材料负载的纳米金属催化剂在芳环选择性加氢反应中的应用研究

发布时间：2018-01-03 00:19

本文关键词：多孔碳氮材料负载的纳米金属催化剂在芳环选择性加氢反应中的应用研究　出处：《浙江大学》2017年博士论文　论文类型：学位论文

【摘要】：芳环化合物选择性加氢反应是化学工业和石油炼制工业中极其重要的反应之一。芳香族化合物种类繁多,具有取代基的芳烃及杂环芳烃的加氢产物是重要的精细化学品,已被广泛用作医药、农药的重要中间体；另一方面,在油品精制工业中,将部分芳烃或烯烃加氢至饱和,可改善油品的使用性能和质量要求。开发高效的多相催化剂是提升芳环加氢技术的关键。我们以廉价易得、可再生的生物质及其衍生物为原料合成氮掺杂炭材料(碳氮材料)。首先以氨基葡萄糖盐酸盐同时作为碳源和氮源,采用水热法制备了介孔碳氮材料(CN)；其次是以纤维素为碳源、草酸铵为氮源、NaHCO_3为活化剂,采用我们课题组首创的“发泡法”制备出具有多级孔道结构的碳氮材料(NHPC)。最后,我们以制备得到碳氮材料作为新颖的催化剂载体材料,负载不同的纳米金属,制备得到碳氮材料负载的纳米金属催化剂,并成功地将这些催化剂应用于催化芳环化合物的选择性加氢反应中,实验和理论计算相结合系统地研究了相关选择性加氢反应的机理。首先,我们采用操作简便、环境友好的超声辅助共还原法在CN上负载了分散均匀、小尺寸(3.6nm)的RuPd双金属纳米粒子(RuPd/CN),将其用于苯甲酸及其衍生物催化加氢反应中。研究发现,RuPd/CN的催化活性远高于相应的单金属催化剂(Pd/CN和Ru/CN),如在同样温和的反应条件(85℃,0.1 MPa H_2,水作溶剂)下,Ru/CN上苯甲酸的转化率为9%,Pd/CN上苯甲酸的转化率为38%,而RuPd/CN上苯甲酸的转化率高达67%。经一系列表征可知,双金属催化剂活性提升的关键是形成了的RuPd合金,Pd的加入提高了Ru~0的比例,从而提高了催化剂的催化活性。在此基础上,我们结合DFT理论计算研究了反应机理。发现苯甲酸在不同催化剂表面的吸附能差异是导致不同H_2压力平台出现的原因。通过构建苯甲酸羧基在不同催化剂上的解离和加氢模型可知,无论在哪种催化剂表面,COOH加氢均是热力学不支持的反应,从而解释了催化剂对苯甲酸的芳环具有超高加氢选择性的原因。其次,我们制备了一系列负载型Ir催化剂,发现其在催化苯甲酸芳环加氢反应中具备超高的催化活性,如Ir/CN 催化剂在相当温和的反应条件(85℃,0.1MPa H_2,水作溶剂)下,反应0.5 h时的TOF值高达34h~(-1)。通过实验排除了不同载体上Ir颗粒的大小、晶形,Ir物种的价态等因素对活性的影响,找出影响其活性的最关键因素是载体在溶液中的分散稳定性。进一步结合DFT理论计算系统地研究了负载型Pt族贵金属催化苯甲酸加氢性能的规律,探究了Ir催化剂具备超高活性的内在原因。研究发现,催化剂上底物与溶剂之间的竞争吸附会极大程度地影响催化剂催化苯甲酸的加氢性能。我们首次提出了不同催化剂上反应底物(H_2)和反应溶剂(H_2O)的解离能/吸附能之差与其催化苯甲酸加氢性能之间存在明显的“火山型”曲线。由此解释了Ir具备超高活性的原因是由于Ir催化剂表面的H_2和H_2O的解离能/吸附能之差处于一个最佳的范围内。最后,我们采用简易的超声辅助NaBH_4还原法在NHPC(氮掺杂的多级孔道炭材料)上负载了分散均匀的Ru纳米粒子(Ru/NHPC),并将其应用于甲苯和喹啉催化加氢反应中。与Ru/HPC (HPC,不掺氮的多级孔炭材料)和Ru/AC(AC,商业活性炭)相比,Ru/NHPC表现出不同寻常的高活性和稳定性。在催化甲苯加氢反应中,100℃、3 MPaH_2的反应条件下,Ru/NHPC的TOF值可高达39000 h~(-1)；在催化喹啉加氢时,在100℃、3MPa H2的反应条件下,Ru/NHPC的TOF值可高达2858h~(-1)。且Ru/NHPC不会被含氮化合物(喹啉及其加氢产物)毒化,具有很好的重复使用性和抗毒化性能,这进一步提高了其在实际生产中的应用潜能。深入研究证实了NHPC中相互贯通的多级孔道结构和掺杂的氮对催化剂的性能提升起到了关键的作用。综上所述,本论文首先基于生物质原料制备了氮掺杂的多孔炭材料,并以此为新颖载体负载了RuPd、Ir、Ru等纳米金属,得到高性能的芳环加氢(苯甲酸、甲苯及喹啉的选择性加氢)催化剂,并结合理论计算对加氢反应的机理进行了深入的研究,指出了氮掺杂对载体及纳米金属电子结构的改变、载体孔道结构、底物与溶剂分子在催化剂表面的竞争吸附是影响相关加氢反应性能的关键因素。这些工作的开展能够为未来进一步设计高效、高选择性加氢催化剂以及相关催化剂的工业应用提供参考。
[Abstract]:Aromatic compounds selective hydrogenation reaction is one of very important chemical industry and oil refining industries. Many kinds of aromatic compounds, hydrogenation products with aromatic and heterocyclic aromatic substituents are important fine chemicals, has been widely used in medicine, pesticide intermediates; on the other hand, in the oil refining industry in the part of the aromatic or olefin hydrogenation to saturation, improve service performance and quality of oil. The development of efficient heterogeneous catalyst is the key to enhance the aromatic ring hydrogenation technology. We use cheap and renewable biomass and its derivatives for the synthesis of nitrogen doped carbon materials (carbon nitrogen material) to first. Glucosamine hydrochloride as carbon source and nitrogen source, mesoporous carbon and nitrogen materials were prepared by hydrothermal method (CN); the second is taking the cellulose as the carbon source, ammonium oxalate as nitrogen source, NaHCO_3 as activator,. Our research group pioneered the "foaming method" preparation of carbon and nitrogen materials with hierarchical porous structure (NHPC). Finally, we prepared carbon nitride material as a catalyst carrier material for novel, load different nanometer metal, preparation of nano gold loaded carbon nitrogen material is a catalyst, and successfully the selective hydrogenation of these catalysts used in catalytic aromatic compounds, to study the related mechanism of selective hydrogenation reaction system combining experimental and theoretical calculation. First, we use simple, environmentally friendly ultrasonic assisted co reduction method on the CN load evenly dispersed, small size (3.6nm) RuPd bimetallic nanoparticles (RuPd/CN), which is used for benzoic acid and its derivatives catalyzed hydrogenation reaction. The study found that the catalytic activity of RuPd/CN is much higher than the corresponding monometallic catalysts (Pd/CN and Ru/CN), as in the same gentle The reaction conditions (85 C, 0.1 MPa H_2, water as solvent), conversion of benzoic acid Ru/CN was 9% and the conversion of benzoic acid on Pd/CN 38%, and RuPd/CN on the conversion of benzoic acid up to 67%. by a series of characterization shows that the key to enhance the activity of the bimetallic catalyst is RuPd alloy form, the addition of Pd increased the proportion of Ru~0, so as to improve the catalytic activity of the catalyst. On this basis, we combine the DFT theory to study the reaction mechanism. The calculation found that benzoic acid adsorption on different catalyst surface differences are caused by different pressure of H_2 platform. The construction of benzoic acid in different carboxyl group dissociation the catalyst and hydrogenation model shows that in either the surface of the catalyst, the hydrogenation of COOH are not supported by thermodynamic reaction, thus explaining the catalyst of benzoic acid with high aromatic hydrogenation selectivity. Second, we The preparation of a series of supported Ir catalysts, that it has high catalytic activity in the catalytic hydrogenation of benzoic acid and aromatic ring, such as the Ir/CN catalyst in the reaction conditions quite modest (85 C, 0.1MPa H_2, water as solvent), the reaction time is 0.5 h and the high TOF value of 34h~ (-1) through the experiments of exclusion of different carriers of Ir particle size, morphology, effect of Ir species valence and other factors on the activity, find out the key factors affecting its activity is the carrier dispersion stability in solution. Further according to the theory of DFT computing system of Pt group supported noble metal catalytic hydrogenation of benzoic acid the performance of the law, explores the intrinsic reason of Ir catalyst have high activities. The study found that the hydrogenation performance of catalyst on the competitive adsorption between substrate and solvent will greatly influence the catalytic catalyst for formic acid. We proposed for the first time with the catalyst The substrate (H_2) and solvent (H_2O) dissociation / adsorption energy difference and the catalytic hydrogenation of benzoic acid to performance between the obvious "Volcano" curve. This explains the reason Ir has high activity is due to the dissociation of Ir H_2 on the surface of the catalyst and H_2O / adsorption energy difference at one of the best range. Finally, we use ultrasonic assisted NaBH_4 simple reduction method in NHPC (hierarchical porous carbon materials doped with nitrogen) loaded Ru nanoparticles dispersed uniformly (Ru/NHPC), and its application in catalytic hydrogenation of quinoline and toluene. And Ru/HPC (HPC, no nitrogen doped hierarchical porous carbon material) and Ru/AC (AC, commercial activated carbon) compared to Ru/NHPC showed unusually high activity and stability. In the catalytic hydrogenation reaction, 100 C, 3 MPaH_2, Ru/NHPC and TOF value can be up to 39000 h~ (-1); in the catalytic hydrogenation of quinoline When, in 100 DEG C, the reaction conditions of 3MPa H2, Ru/NHPC TOF value can be as high as 2858h~ (-1). And Ru/NHPC will not be nitrogenous compounds (quinoline and its hydrogenation product) with repeated use of poison, and good anti poisoning performance, which further improves the application potential in practical production.. further study confirmed that the NHPC interconnected hierarchical structure and doping of nitrogen on the catalytic performance of the catalyst promotion plays a key role. In summary, this paper based on nitrogen doped porous carbon materials prepared from biomass raw materials, and as a novel carrier to load RuPd, Ir, Ru and other metal nanoparticles, get high performance aromatic ring hydrogenation (benzoic acid, toluene and selective hydrogenation of quinoline) catalyst, and the theoretical calculation mechanism of hydrogenation reaction were studied, pointed out that the change of nitrogen doping on the electronic structure and nano metal carrier, carrier The pore structure, substrate and solvent molecules is a key factor affecting the related hydrogenation in competitive adsorption on the catalyst surface. These work can provide reference for future design of high efficiency, industrial application of high selective hydrogenation catalyst and catalyst.

【学位授予单位】：浙江大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：O643.36

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