水热法制备过渡金属磷化镍及其加氢脱氯性能的研究

发布时间：2018-03-28 02:12

  本文选题：磷化镍　切入点：水热合成　出处：《东南大学》2017年硕士论文

【摘要】：过渡金属磷化物作为一种新型催化剂,在光学、电磁学等多个领域均表现出卓越性能,使其一度成为热门的研究课题。磷化镍,作为一种重要的过渡金属磷化物,在多类涉氢反应中均表现出较高的活性和稳定性。磷化镍具有多种可调节的组成比,如Ni2P、Ni12P5、Ni3P和Ni5P2等,这就使得制备单一晶相组成的磷化镍成为一个难题。而本文另一个重要的研究物质——三氯乙烯(TCE),作为脱脂剂、干洗剂和制冷剂等,广泛用于生产生活中。正因为如此,三氯乙烯是当前环境中分布最广的污染物之一。在各种降解方法中,加氢脱氯被证明是一种最安全有效的降解方法。本文采用水热法制备出一系列不同组成的磷化镍,并在制备过程中加入表面活性剂聚乙二醇(PEG)或聚乙烯吡咯烷酮(PVP),得到四方晶型和六方晶型两种晶型的磷化镍。同时,通过各种表征手段(X射线衍射、扫描电镜、透射电镜和比表面积测定等),探讨了磷化镍不同晶型结构的形成机理,并将磷化镍应用于三氯乙烯的加氢脱氯反应中,来测定其催化性能,得到以下结论:(1)磷化镍的制备条件(反应物初始配比(Ni/P)、反应温度、反应时间和溶剂)直接影响其最终组成。实验表明:在Ni/P≥1/2、T彡180℃或者t≥48h时,有利于Ni12P5生成,反之,更有利于Ni2P生成;而溶剂中乙二醇的加入会使部分Ni2P 转变成 Ni12P5。(2)PEG和PVP对磷化镍的晶型结构具有调控作用,但两者的作用机理完全不同。当溶液中PEG的浓度达到临界胶束浓度时,其亲水性一端会按一定优先次序吸附在Ni2P晶面上,被吸附的晶面就停止生长,这种择优吸附改变了晶体在各个方向上的生长率,最终导致六方晶型的Ni2P逐渐转变成四方晶型的Ni12P5;而PVP具有还原性,浓度增大,还原能力增强,最终形成了氧化性更弱的Ni12P5°(3)PVP对磷化镍的粒径具有调节作用。在其作用下,磷化镍由不规则大块状转变成由均一小颗粒联接而成的三维孔道结构。(4)磷化镍中加入表面活性剂进行改性后,加氢脱氯活性比原来可提高2-3倍,同时,最佳活性温度降低,活性温度区间变宽。
[Abstract]:As a new type of catalyst, transition metal phosphates have shown excellent performance in many fields, such as optics, electromagnetics and so on. Nickel phosphide has a variety of adjustable composition ratios, such as Ni _ 2P, Ni _ (12) P _ (5) Ni _ (3P) and Ni5P2, etc. This makes the preparation of single crystalline nickel phosphide a difficult problem. Another important research substance in this paper, trichloroethylene (TCE), is widely used in production and life as degreasing agent, dry cleaning agent and refrigerant. Trichloroethylene (trichloroethylene) is one of the most widely distributed pollutants in the environment. Hydrodechlorination has been proved to be the safest and most effective degradation method in various degradation methods. A series of nickel phosphide with different compositions were prepared by hydrothermal method in this paper. The tetragonal and hexagonal forms of nickel phosphide were obtained by adding the surfactant PEG (polyethylene glycol) or polyvinylpyrrolidone (PVP) in the preparation process. At the same time, X-ray diffraction and scanning electron microscopy were used to characterize the nickel phosphide. The formation mechanism of different crystalline structure of nickel phosphide was discussed by transmission electron microscope and specific surface area measurement. The catalytic activity of nickel phosphide was determined by applying it to hydrodechlorination of trichloroethylene. The following conclusion is drawn: the preparation conditions of nickel phosphide (the initial ratio of reactants, reaction temperature, reaction time and solvent) directly affect the final composition of nickel phosphide. The experimental results show that when Ni/P 鈮，

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