贵金属基催化剂设计、制备及其催化氧化苯的性能研究

发布时间：2018-05-15 06:25

本文选题：贵金属 + 多孔结构　；参考：《中国科学院大学(中国科学院过程工程研究所)》2017年博士论文

【摘要】：挥发性有机化合物(VOCs)严重威胁到人类的健康及环境的安全,因而越来越多的学者致力于其净化技术的研究。其中,催化氧化的方法因其低能耗、快速、操作安全且环境友好等特点,受到人们的广泛关注。目前,贵金属和金属氧化物催化剂是降解VOCs的两种主要典型催化剂。在近几十年来,随着制备、表征技术和测试手段的不断发展,纳米结构材料的合成与应用研究已经得到了蓬勃发展,这便给纳米材料如何在催化净化VOCs领域内得到高效利用,带来了巨大的机遇与挑战。对此,本文针对贵金属基纳米催化剂,以提高单位贵金属催化剂的效率为目标,通过结构控制及界面改性的手段,探索催化剂结构、形貌与催化性能之间的关系。主要研究内容和结果如下:(1)将Co基金属有机骨架结构(Co-MOF,Co-based ZIF-67)在不同温度下焙烧,其有机骨架去除程度不同,因而得到的孔结构、颗粒大小及金属的化学价态均有所不同,这将影响反应物的分布情况及催化剂表面活性氧的性质,从而影响催化剂的活性。高比表面积和丰富的孔结构有利于催化剂活性位点的暴露,即有利于反应物和表面氧的吸附及反应。在Pd/Co_3O_4-PP-350上,由Pd到O的电子转移可以使Oads更为活跃。这也得到H2-TPR测试结果的验证,即Pd/Co_3O_4-PP-350上的PdOx还原性最优,其上的氧活性最高。因此,Pd/Co_3O_4-PP-350对苯的完全氧化反应表现出最优的催化活性。(2)在Pt/Al_2O_3催化剂中加入还原氧化石墨烯(rGO)助剂,可以有效提高催化剂的比表面积;同时通过XPS测试还发现催化剂的Oads轨道电子结合能低时,其T90也更低一些,当催化剂具有更高的Oads轨道电子结合能时,其T90也会高一些。这说明Oads在苯的完全氧化反应中起着至关重要的作用。而在Pt-rGO/Al_2O_3催化剂中,电子由rGO转移至Pt和O,可降低Oads轨道电子结合能,使表面吸附氧更为活跃,从而提高催化剂的性能。(3)采用液相法对活性组分Pt的形貌进行精细调控。通过对反应温度和Ag(或Au)添加量的控制,可以有效调控Pt的形貌,最终获得枝状和球形的Pt纳米颗粒。将这些颗粒应用于催化剂的制备,并对得到的催化剂进行苯的催化及其他表征测试。结果表明,枝状Pt/Al_2O_3催化剂上,表面活性氧更多,且更为活跃。因此,与球状Pt/Al_2O_3催化剂相比,其在苯完全氧化反应中表现出更为优异的催化活性。(4)采用液相法在油胺中还原获得Cu含量不同的Pt-Cu颗粒,并将其负载在γ-Al_2O_3上进行活性和表征测试。由于制得的催化剂中,除Cu含量不同外,其负载量,分散度,形貌均存在较大差异,因此,很难在催化剂的性质与活性之间找到直接相关的简单规律。但可以发现催化剂的TOF与其上Pt颗粒的模型计算粒径正相关,进而发现催化剂的活性与其表面的Pt原子数和Pt颗粒模型计算粒径之间存在正相关关系。因此,需找出催化剂表面Pt原子数和Pt颗粒模型计算粒径的平衡值,以便使催化剂的活性达到最大。另外,催化剂中,lPt-lCu/Al_2O_3的活性最优。
[Abstract]:Volatile organic compounds (VOCs) seriously threaten the safety of human health and environment, and more and more scholars have been devoted to the study of its purification technology. Among them, catalytic oxidation has attracted wide attention because of its low energy consumption, rapid operation, safe operation and environmental friendliness. It is the two major typical catalysts for the degradation of VOCs. In the past few decades, with the continuous development of preparation, characterization and testing methods, the synthesis and application of nanostructured materials have been flourishing. This has brought great opportunities and challenges on how nanomaterials can be utilized efficiently in the field of catalytic purification of VOCs. In this regard, the relationship between the structure of the catalyst and the catalytic properties of the catalyst is explored by means of structural control and interfacial modification. The main contents and results are as follows: (1) the Co based metal organic framework structure (Co-MOF, Co-based ZIF-67) is used as a result of structural control and interfacial modification. The removal of organic skeleton is different at different temperatures, thus the structure of the pores, the size of the particles and the chemical valence state of the metal are different. This will affect the distribution of the reactants and the properties of the surface active oxygen of the catalyst, thus affecting the activity of the catalyst. The high specific surface area and the rich pore structure are beneficial to the activity of the catalyst. The exposure of the loci is beneficial to the adsorption and reaction of the reactant and surface oxygen. On Pd/Co_3O_4-PP-350, the electron transfer from Pd to O can make Oads more active. It is also verified by the results of the H2-TPR test that the PdOx reducibility on Pd/Co_3O_4-PP-350 is optimal and the highest oxygen activity on it. Therefore, the complete oxidation of Pd/Co_3O_4-PP-350 to benzene has been obtained. The reaction shows the best catalytic activity. (2) adding the reductive graphene oxide (rGO) additive in the Pt/Al_2O_3 catalyst can effectively improve the specific surface area of the catalyst. At the same time, the XPS test also found that when the Oads orbital electron binding energy of the catalyst is low, the T90 is lower, when the catalyst has a higher Oads orbital electron binding energy. The T90 will also be higher. This indicates that Oads plays a vital role in the complete oxidation of benzene. In the Pt-rGO/Al_2O_3 catalyst, the electron transfer from rGO to Pt and O can reduce the electron binding energy of the Oads orbit, make the surface adsorbed more active, and thus improve the sexual energy of the catalyst. (3) the liquid phase method is applied to the morphology of the active component Pt. Fine control. Through the control of the reaction temperature and the amount of Ag (or Au) addition, the morphology of the Pt can be effectively controlled and the Pt nanoparticles with branches and spheres are finally obtained. These particles are applied to the preparation of the catalyst, and the catalytic and other characterization tests of the obtained catalysts are carried out. The results show that the surface of the branched Pt/Al_2O_3 catalyst is on the surface. The active oxygen is more active and more active. Therefore, compared with the spherical Pt/Al_2O_3 catalyst, it has more excellent catalytic activity in the complete oxidation of benzene. (4) the Pt-Cu particles with different Cu content are obtained by the liquid phase method in the oil amine, and the activity and characterization of the particles are loaded on the gamma -Al_2O_3. In addition to the different Cu content, the load, the dispersion and the morphology of the catalyst are very different. Therefore, it is difficult to find a direct correlation between the properties and the activity of the catalyst. But it is found that the TOF of the catalyst is positively correlated with the size of the upper Pt particles, and the activity of the catalyst and the number of Pt atoms and Pt on the surface of the catalyst are also found. There is a positive correlation between particle size and particle size. Therefore, the balance between the number of Pt atoms on the surface of the catalyst and the calculation of the equilibrium value of the particle size of the Pt particle model should be found so that the activity of the catalyst can be maximum. In addition, the activity of lPt-lCu/Al_2O_3 is best in the catalyst.

【学位授予单位】：中国科学院大学(中国科学院过程工程研究所)
【学位级别】：博士
【学位授予年份】：2017
【分类号】：X505;O643.36

【参考文献】