锡锌氧化物负载的金催化剂在一氧化碳氧化反应中的“构效”关系研究

发布时间：2018-08-15 15:29

【摘要】：文章由两个独立部份构成:基于一氧化碳(CO)氧化的金基系列催化剂“构效关系”研究和应用于丙烯环氧化的钼基系列催化剂初步研究。CO一直是重要的空气污染源,长久以来研究者们在为寻求高效的CO催化氧化催化剂而不懈的努力,作为一类新型催化剂金负载金属或非金属氧化物一直受到人们的关注,在长期的研究中人们发现金的结构和载体的特性对催化剂的性能起着至关重要的作用,在所有的研究体系中人们得到了一个共识性的结论:载体中氧空位的含量对催化剂的性能有着非常重要的作用。目前已经研究的载体有:Fe_2O_3,CeO2,ZnO2,Al2O3,CuO,TiO_2,Co_3O_4,SnO_2等。锡锌复合氧化物(Zn_2SnO_4)是一类类钙钛矿化合物,它具有高质子导率、丰富的氧空位,目前主要应用于太阳能电池,气体传感器,光催化剂等方面,目前还没有相关工作报道Zn_2SnO_4作为载体负载金催化CO氧化的报道,他是否是一类良好的载体,其结构对Au的尺寸和结构有何影响,Au/Zn_2SnO_4的结构与活性存在着怎么样的关系等等都不得而知,据此本文对Au/Zn_2SnO_4催化剂的“构效”关系进行了研究。本工作之一,利用沉积沉淀法将0.7 wt.%金负载在一类新型氧化物载体——锌锡复合氧化物(Zn_2SnO_4)上,而载体的织构性质可由碱水合肼(N_2H_4·xH_2O)与金属离子(Zn~(2+))比例在4/1、8/1和16/1之间进行调节。我们发现当N_2H_4·xH_2O/Zn~(2+)=8/1时金催化剂表现出最高活性,而当N_2H_4·x H_2O/Zn~(2+)=16/1时活性则降低至接近纯Zn_2SnO_4载体。我们利用氮气吸脱附、X射线衍射谱(XRD)、透射电子显微镜(TEM)、高角环形暗场-扫描透射电子显微镜(HAADF-STEM)、X射线光电子能谱(XPS)、X射线吸收精细结构谱(XAFS)以及氢气程序升温还原(H2-TPR)等表征技术对于反应前后的金催化剂进行了深入的结构探测,结果发现载体氧化物的织构(孔体积和孔径分布)对于金的颗粒尺寸至关重要,从而决定了Au-Zn_2SnO_4催化剂的活性。环氧丙烷是重要的基本有机化工原料。本文工作之二着重研究开发一种新的催化剂使反应过程由多步变为从丙烯经过分子氧,直接一步生产环氧丙烷。MoO_3/SiO_2具有较高的丙烯环氧化催化能力,已经取得的研究也表明Bi-P-Mo基体系的丙烯环氧化遵循自由基反应机理,SiO_2负载的TiO_2催化剂表现出良好的PO产率和选择性,本实验我们对材料的制备方法及助剂的加入对催化剂的形貌影响进行了初步的研究。结果显示,助剂K+的修饰对MoO_3-SiO_2样品形貌有非常大的影响,加入顺序不同MoO_3完全呈现出不同的形貌,先加K+修饰最后得到的MoO_3呈现球状,后加K+修饰最后得到的MoO_3呈现出针状。Na+的修饰对MoO_3-TiO_2形貌几乎无影响,结果没有明显的差异。另外文章还采用了其他的合成方法如水热合成法、溶胶凝胶合成法来制备Mo基和Ti基催化剂,发现溶胶凝胶法制备的MoO_3-SiO_2催化剂结晶度较浸渍法好,水热法合成的所有样品中X射线衍射仪(XRD)显示均呈现载体的物相,X射线吸收精细结构谱(XAFS)分析显示Mo在催化剂中以氧化态形式存在。
[Abstract]:This paper consists of two independent parts: the "structure-activity relationship" of gold-based catalysts for CO oxidation and the preliminary study of molybdenum-based catalysts for propylene epoxidation. As a new type of catalysts, GOLD-SUPPORTED metal or non-metallic oxides have attracted much attention. In the long-term studies, it has been found that the structure and support properties of gold play an important role in the performance of catalysts. Tin-zinc complex oxides (Zn_2SnO_4) are a kind of perovskite compounds with high proton conductivity and abundant oxygen vacancies. At present, they are mainly used in solar cells, gas sensors and photocatalysis. There are no reports on the catalytic oxidation of CO with gold supported on Zn_2SnO_4 as a carrier. It is not known whether Zn_2SnO_4 is a good carrier, how its structure affects the size and structure of Au, and how the structure of Au/Zn_2SnO_4 is related to its activity. In this work, 0.7 wt.% gold was loaded on a new type of oxide carrier, zinc-tin complex oxide (Zn_2SnO_4). The texture properties of the carrier can be adjusted by the ratio of alkaline hydrazine hydrate (N_2H_4.xH_2O) to metal ions (Zn~ (2+) between 4/1, 8/1 and 16/1. Nowadays, the gold catalyst exhibits the highest activity when N_2H_4.xH_2O/Zn~ (2+) = 8/1, but when N_2H_4.xH_2O/Zn~ (2+) = 16/1, the activity decreases to nearly pure Zn_2SnO_4. Nitrogen adsorption and desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), high angle ring dark-field scanning transmission electron microscopy (HAADF-STEM), X-ray photoelectron microscopy (XPM), etc. Energy dispersive spectroscopy (XPS), X-ray absorption fine structure spectroscopy (XAFS) and hydrogen temperature programmed reduction (H2-TPR) were used to investigate the structure of gold catalysts before and after the reaction. It was found that the texture (pore volume and pore size distribution) of supported oxides was very important to the size of gold particles, which determined the size of Au-Zn_2SnO_4 catalyst. Propylene oxide is an important basic organic chemical material. The second part of this paper focuses on the research and development of a new catalyst for the direct one-step production of propylene oxide from propylene through molecular oxygen instead of multi-step reaction. MoO_3/SiO_2 has a high catalytic capacity for propylene epoxidation. The results also show that Bi-P-Mo matrix has been obtained. The epoxidation of propylene follows the mechanism of free radical reaction. SiO_2 supported TiO_2 catalyst exhibits good PO yield and selectivity. In this experiment, we studied the preparation method of the material and the effect of the addition of promoters on the morphology of the catalyst. The results show that the modification of promoter K+ has a very large effect on the morphology of MoO_3-SiO_2 sample. MoO_3 is spherical after K + modification, and acicular MoO_3 after K + modification. Na + modification has little effect on the morphology of MoO_3-TiO_2, and there is no obvious difference in the results. In addition, other synthetic methods such as hydrothermal synthesis, dissolution are also used. Mo-based and Ti-based catalysts were prepared by sol-gel method. It was found that the crystallinity of Mo_3-SiO_2 catalysts prepared by sol-gel method was better than that by impregnation method. All samples synthesized by hydrothermal method showed that the supported phase was observed by X-ray diffraction (XRD). X-ray absorption fine structure spectroscopy (XAFS) analysis showed that Mo existed as oxidized state in the catalyst.
【学位授予单位】：中国科学院研究生院(上海应用物理研究所)
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：O643.36

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