可控的核壳结构镍基催化剂水热制备原理及其应用

发布时间：2018-01-13 23:07

本文关键词：可控的核壳结构镍基催化剂水热制备原理及其应用　出处：《华东师范大学》2017年硕士论文　论文类型：学位论文

【摘要】：镍基催化剂因其低成本和高活性等优势被广泛应用于多种催化工业过程。我们设计将氢型的单晶HBEA分子筛投入到NH4Cl/NH3·H20缓冲溶液,通过一种可调控的水热合成方法得到壳层结构的Ni/HBEA。该种催化剂保持了 HBEA分子筛的晶体形貌,大量的高分散镍纳米颗粒主体分布于分子筛表面,少量纳米颗粒封装于分子筛介孔内部(担载量41 wt%,颗粒尺寸5.9 ±0.7 nm)。我们通过X射线衍射(XRD),扫描电子显微镜(SEM),高倍透射电子显微镜(TEM),氮气吸附,电感耦合等离子体原子发射光谱(ICP-AES),傅里叶红外光谱(IR),吡啶为探针分子的红外光谱(IR-Py),程序升温还原(TPR)及固体核磁(solid NMR)等表征手段不仅确定了 Ni/HBEA的壳层结构,并探究认为水热合成经历了溶硅-硅酸镍的两步反应过程。其中溶硅过程为决速步,当溶解的硅含量大于一定值时,层状结构的硅酸镍快速生成。当使用NH_4Cl为单一沉淀剂时,溶液环境无法达到溶硅要求。而当使用NH_3·H_2O为单一沉淀剂时,NH_3·H_2O不仅破坏了分子筛的结构形貌,并且加速了决速步的进行,使得中间物质由动力学控制的1:1型硅酸镍(Ni_3Si_2O_5(OH)_4)转化为热力学有利的2:1型硅酸镍(Ni_3Si_4O_(10)(OH)_2)。所得的催化剂在硬脂酸加氢脱氧反应中表现出极高的反应活性,速率达到54g·g-1·h-1。另外,我们提出了一种利用水作为溶剂的新型绿色的简易水热方法制备各分子筛(HBEA,HUSY,HZSM-5,HMOR)的过渡金属催化剂。该种方法中,我们将弱酸弱碱盐,分子筛直接加入水中,无需任何沉淀剂,稳定剂,表面活性剂等的添加。因此在制备结束后,所得催化剂不需要水洗,且滤液相对纯净可以循环使用,为解决废水排放的问题提出了新的思路。且催化剂的镍担载量可以通过反应时间控制,镍纳米颗粒的分布因硅酸镍中间产物的形成而被控制。根据这一溶硅-形成硅酸镍的两步过程,具有弱碱性的镍盐以及合适骨架密度的载体组合最优。和传统的制备方法如沉积沉淀法,浸渍法相比,所得到的高镍担载量的催化剂在加氢脱氧反应,氢化反应中具有更高的反应活性及选择性。
[Abstract]:Nickel based catalysts have been widely used in many industrial processes due to their advantages of low cost and high activity. Hydrogen type single crystal HBEA molecular sieve was designed to be used in NH4Cl/NH3 路H20 buffer solution. Ni- / HBEA with shell structure was obtained by a controllable hydrothermal synthesis method. The crystal morphology of HBEA molecular sieve was maintained by the catalyst. A large number of highly dispersed nickel nanoparticles are mainly distributed on the surface of molecular sieve, and a small number of nanoparticles are encapsulated in the mesoporous structure of molecular sieve (the loading capacity is 41 wt%). The particle size is 5.9 卤0.7 nm 路m ~ (-1). X ray diffraction (XRD), scanning electron microscopy (SEM), high power transmission electron microscopy (TEM) and nitrogen adsorption are used. Inductively coupled plasma atomic emission spectroscopy (ICP-AESN), Fourier transform infrared spectroscopy (FTIR), and pyridine as probe molecule (IR-Pyr). Temperature programmed reduction (Ni/HBEA) and solid NMR (solid NMR) not only confirmed the shell structure of Ni/HBEA. It is concluded that hydrothermal synthesis has undergone two steps of dissolution of silicon and nickel silicate, in which the dissolution of silicon is a rapid step, when the content of dissolved silicon is greater than a certain value. When NH_4Cl was used as a single precipitant, the solution environment could not meet the requirements of dissolved silicon, but when NH_3 路H _ 2O was used as a single precipitating agent. NH_3 路H _ 2O not only destroyed the structure and morphology of molecular sieve, but also accelerated the speed step. Conversion of intermediate matter from 1: 1 type nickel silicate to Nis _ 3Si _ 2O _ 5O _ H _ 4) to thermodynamically advantageous Ni3Si _ 4O _ s _ _ _. The obtained catalyst exhibited very high activity in the hydrodeoxidation of stearic acid. The rate reached 54g 路g -1 路h-1.In addition, a new green hydrothermal method using water as solvent was proposed for the preparation of HZSM-5 with different molecular sieves HBEAA HUSYY and HZSM-5. HMOR) transition metal catalyst. In this method, we add weak acid and weak base salt and molecular sieve directly into water without any addition of precipitators, stabilizers, surfactants, etc. The obtained catalyst does not need washing and the filtrate is relatively pure and can be recycled. A new idea is put forward to solve the problem of wastewater discharge, and the nickel load of the catalyst can be controlled by reaction time. The distribution of nickel nanoparticles is controlled by the formation of nickel silicate intermediate products. Compared with the traditional preparation methods such as deposition method and impregnation method, the catalyst with high nickel loading was obtained in the hydrogenation deoxidation reaction. The hydrogenation reaction has higher activity and selectivity.
【学位授予单位】：华东师范大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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