电纺PAN基碳纤维载镍复合催化剂在Heck反应中的应用研究

发布时间：2018-06-07 14:38

本文选题：电纺丝技术 + 镍纳米粒子　；参考：《内蒙古工业大学》2017年硕士论文

【摘要】：分布广泛的镍基纳米材料由于价格低廉受到广大研究者的关注。而以镍基复合材料作为催化剂,得到了更广泛的研究。其中对于Heck反应的研究已经具有了一定的深度,对于钯基催化剂,负载型镍基催化剂具有独特的优点。本文结合静电纺丝、氢气还原以及高温碳化技术,制备了具有良好形貌、高效催化活性以及可循环使用的镍基碳纳米纤维复合催化剂,具体研究如下:(1)利用静电纺丝技术为基础制备以无机氯化镍为镍源的纳米纤维膜,结合两种还原方法(氢气高压还原和氢氩混合气常压高温还原)制备镍碳纤维复合材料(Ni/CNFs)。通过系列表征方法对两种镍基纤维复合材料的纤维形貌、镍纳米粒子尺寸及分布和镍的价态进行了详细的检测分析:表明制备的复合催化剂具有好的纤维形貌且粒径较小的镍纳米粒子在碳纤维中均匀分布,纳米镍以面心立方结构晶型存在并为零价镍。通过Heck反应考察了两种复合材料的催化性能,当碳化温度为500°C时两种催化剂催化Heck反应均具有较好的转化率。比较两种不同镍基催化剂的催化结果,确定:高压氢气还原法制备的Ni(0)/CNFs具有较好的催化性能,故最适合的还原条件为高压氢气还原。(2)结合上述研究,以乙酰丙酮镍盐为镍源,结合静电纺丝技术,利用高压氢气还原以及高温碳化制备了Ni/CNFs。通过SEM、TEM、XPS等表征结果表明Ni/CNF排列整齐、光滑无节点,镍纳米粒子分布均匀、尺寸均一,并且形成了零价镍。根据Heck反应结果表明,与无机镍盐比较,有机镍盐为镍源制备的催化剂更稳定,催化及循环性能更好,且具有一定的底物拓展能力。(3)为了提升机镍盐制备镍基催化剂的催化性能,引入造孔剂聚甲基丙烯酸甲酯(PMMA)。通过对材料的表征,确定制备的镍基多孔复合催化剂(Ni/PCNFs)具有良好的形貌和镍纳米粒子的分布,并形成了多孔结构,直径分布在3 nm左右的零价镍纳米粒子均匀分布在碳纤维载体中。造孔剂有效的改善了催化性能偏低的缺点。碳化过程中PMMA分解,并在碳纤维上形成了孔结构,从而增加了底物与镍活性位点的接触,提高了反应速率和转化率。所以,制备的多孔碳纤维载镍复合催化剂对Heck反应具有更高效的催化性能。综上所述,本文主要以静电纺丝技术为基础,利用氢气还原以及高温碳化过程制备了可循环且高效的碳纤维负载镍复合催化剂。碳纤维承载镍基复合催化剂具有优异的性能,有望取代钯等贵金属催化剂,并广泛应用于Heck反应中。碳纤维不仅作为金属载体,碳具有一定的还原性还可以进一步保护制备的零价镍纳米粒子。负载型镍基催化剂不仅仅在研究中展现出潜在的价值,而且在工业产业中也将具有应用价值。
[Abstract]:Widely distributed nickel-based nanomaterials have attracted much attention due to their low price. The nickel matrix composite was used as catalyst, and more extensive research was carried out. The study of Heck reaction has a certain depth, and the supported nickel catalyst has a unique advantage for palladium based catalyst. In this paper, nickel based carbon nanofiber composite catalysts with good morphology, high catalytic activity and recyclability were prepared by electrospinning, hydrogen reduction and high temperature carbonization. The main results are as follows: (1) using electrospinning technology to prepare nanofiber membrane with inorganic nickel chloride as the source, and combining two reduction methods (hydrogen reduction under high pressure and hydrogen argon mixture at atmospheric pressure and high temperature reduction) to prepare Ni / CNFsO / Ni / CNFsN composite. The fiber morphology of two kinds of nickel matrix fiber composites was characterized by a series of characterization methods. The size and distribution of nickel nanoparticles and the valence states of nickel were analyzed in detail. The results showed that the prepared composite catalysts had good fiber morphology and the smaller nickel nanoparticles were uniformly distributed in carbon fiber. Nanocrystalline nickel exists in the crystal form of face centered cubic structure and is zero valence nickel. The catalytic properties of the two composite materials were investigated by Heck reaction. When the carbonization temperature was 500 掳C, the catalytic activity of the two catalysts for Heck reaction was better. Comparing the catalytic results of two kinds of nickel based catalysts, it is determined that the Ni(0)/CNFs prepared by high pressure hydrogen reduction method has better catalytic performance, so the most suitable reduction condition is high pressure hydrogen reduction. (2) combined with the above research, the nickel acetylacetone salt is used as nickel source. Ni / CNFs were prepared by high pressure hydrogen reduction and high temperature carbonization combined with electrostatic spinning technology. The results showed that the Ni/CNF was neatly arranged, smooth without nodes, uniform distribution of nickel nanoparticles, uniform size, and the formation of zero-valence nickel. According to the results of Heck reaction, compared with inorganic nickel salt, the catalyst prepared by organic nickel salt is more stable, and its catalytic and cycling performance is better than that of inorganic nickel salt. In order to improve the catalytic performance of nickel salt to prepare nickel based catalyst, a pore-making agent polymethyl methacrylate (PMMA) was introduced. Through the characterization of the material, it was confirmed that the prepared Ni-base porous composite catalyst (Ni / PCNFs) had good morphology and distribution of nickel nanoparticles, and formed a porous structure. Nickel nanoparticles with a diameter of about 3 nm were uniformly distributed in carbon fiber carriers. The pore-making agent can effectively improve the low catalytic performance. During carbonation, PMMA was decomposed, and the pore structure was formed on carbon fiber, which increased the contact between substrate and nickel active site, and increased the reaction rate and conversion rate. Therefore, the prepared porous carbon fiber supported nickel composite catalyst has a more efficient catalytic performance for Heck reaction. In conclusion, based on electrostatic spinning technology, carbon fiber supported nickel composite catalysts were prepared by hydrogen reduction and high temperature carbonization. Carbon fiber supported nickel based composite catalysts have excellent performance and are expected to replace palladium and other noble metal catalysts and are widely used in Heck reactions. Carbon fiber is not only used as metal carrier, but also can protect the prepared nickel nanoparticles. Supported nickel based catalysts not only show potential value in research, but also have application value in industrial industry.
【学位授予单位】：内蒙古工业大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O621.251

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