CuMnO_x、VMnO_x微纳米结构的制备及催化CO氧化性能研究

发布时间：2018-01-19 05:13

  本文关键词： CO氧化 铜锰氧化物 钒 掺杂 OMS-2　出处：《河南师范大学》2016年硕士论文　论文类型：学位论文

【摘要】：CO催化氧化是一个在室内空气净化、气体传感器、CO_2激光器、汽车尾气处理等方面有着广泛应用的重要反应。尽管人们一直致力于CO催化氧化的贵金属催化剂如:Au/TiO_2、Au/ZrO_2、Pt/SnO_2等的研究、但探索活性高、稳定性好、成本低的非贵过渡金属氧化物催化剂仍具有重要价值。本论文主要研究CuMnO_x和VMnO_x微纳米结构的制备、表征及其在CO催化氧化反应中的性能,论文可分为三大部分。第一部分,以混合草酸盐为前驱体采用一锅热解法合成了一系列铜锰氧化物催化剂,借助X射线衍射(XRD)、N_2物理吸附、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)和程序升温还原(TPR)等手段对催化剂进行了表征,并探究了其在CO氧化反应中的催化性能。为了进一步改善铜锰氧化物的催化性能,我们还探讨了老化时间、焙烧温度等对其结构、组成以及催化氧化CO性能的影响。实验结果表明,采用一锅热法制备的CuMnO_x催化剂能够获得较单一的尖晶石CuMn_2O_4相,且具有较大的比表面积和孔体积,能够为催化CO氧化反应提供更多的Cu-O-Mn界面,故催化剂活性较高。提高焙烧温度能提高CuMn_2O_4的结晶度,但是会相应地降低CuMn_2O_4的比表面积和孔体积,使得暴露的Cu-O-Mn界面减少,从而导致CO氧化反应活性降低。第二部分,采用三种不同方法合成了OMS-2,并通过浸渍法负载铜制备CuO/OMS-2催化剂,借助XRD、N_2物理吸附、XPS、TPR等表征方法探讨了催化剂结构与性能关系。实验结果表明,采用研磨法制备OMS-2比表面积大、能形成大量的吸附位,使得负载的氧化铜以高分散形式存在,能够为CO氧化反应的进行提高更多的Cu-O-Mn界面,故催化活性较高。而采用回流法和水热法制备的OMS-2为针状或纤维状形貌、比表面积小,导致OMS-2表面存在大量聚集态氧化铜,所能获得Cu-O-Mn界面大大减少,故催化活性显著降低。第三部分,采用回流法制备了一系列不同钒源和不同钒锰比的V-OMS-2催化剂,详细考察其在CO催化氧化反应中的催化性能,并借助XRD、N_2物理吸附、Raman、XPS、TPR等谱学方法对催化剂进行了表征。实验结果表明,以V_2O_5为钒源制备的V-OMS-2-O为纳米棒状结构、比表面积大,而其它两种钒源制备的样品比表面积较小。另外,以V_2O_5为钒源制备的V-OMS-2-O表面晶格氧的活泼性和反应性也明显强于其它两种钒源制备的催化剂,这使得V-OMS-2-V-O表现出更高的催化活性。掺杂少量的V(3%)能够大幅度提高OMS-2的比表面积,且掺杂的V均以+5价离子形式替代Mn~(4+)进入OMS-2的骨架结构中,显著改变了锰氧八面体位周围O的配位环境,增加了表面晶格氧的活泼性和反应性,因而能够明显改善OMS-2在CO氧化反应中的催化活性。当V掺杂量为3%时,V-OMS-2-O的催化活性最高,100%CO转化时反应温度降至50℃左右。过量的钒(6%)将导致OMS-2的孔道结构破坏,钒在锰氧化物表面富积,严重影响锰氧化物表面晶格氧的活泼性和反应性,导致催化剂活性降低。
[Abstract]:Co catalytic oxidation is a CO _ 2 laser with a gas sensor for indoor air purification. Automobile tail gas treatment has been widely used in many important reactions, although people have been dedicated to CO catalytic oxidation of noble metal catalysts such as: Au/ TiO2 / Au/ ZrO2. Pt/SnO_2 et al., but the exploration activity is high and the stability is good. Low-cost non-expensive transition metal oxide catalysts are still of great value. In this thesis, the preparation of CuMnO_x and VMnO_x microstructures is studied. In the first part, a series of copper-manganese oxide catalysts were synthesized by one-pot pyrolysis with mixed oxalate as precursor. Physical adsorption of N2 by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The catalysts were characterized by X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). In order to further improve the catalytic performance of Cu-Mn oxide, we also discussed the aging time, calcination temperature and so on. The experimental results show that the single spinel CuMn_2O_4 phase can be obtained from the CuMnO_x catalyst prepared by one-pot thermal method. And it has a large specific surface area and pore volume, which can provide more Cu-O-Mn interface for the catalytic CO oxidation reaction. Therefore, the activity of the catalyst is high. The crystallinity of CuMn_2O_4 can be increased by increasing the calcination temperature, but the specific surface area and pore volume of CuMn_2O_4 will be reduced accordingly. The exposed Cu-O-Mn interface was reduced, which resulted in the decrease of CO oxidation activity. In the second part, three different methods were used to synthesize OMS-2. The CuO/OMS-2 catalyst was prepared by impregnation method supported on copper. TPR and other characterization methods were used to investigate the relationship between the structure and performance of the catalyst. The experimental results showed that the preparation of OMS-2 by grinding method had large specific surface area and formed a large number of adsorption sites. The supported copper oxide exists in the form of high dispersion, which can improve the Cu-O-Mn interface for CO oxidation. Therefore, the catalytic activity is higher. However, the OMS-2 prepared by reflux method and hydrothermal method is acicular or fibrous, and the specific surface area is small, resulting in a large number of aggregate copper oxide on the surface of OMS-2. In the third part, a series of V-OMS-2 catalysts with different vanadium sources and different vanadium / manganese ratios were prepared by reflux method. Its catalytic performance in CO catalytic oxidation reaction was investigated in detail, and Raman XPS was obtained by means of XRDX / N2 physical adsorption. The catalyst was characterized by TPR and the experimental results showed that V-OMS-2-O with V _ S _ 2O _ 5 as vanadium source had a large specific surface area. However, the specific surface area of the samples prepared by the other two vanadium sources is smaller. The surface lattice oxygen activity and reactivity of V-OMS-2-O prepared by V _ 2O _ 5 as vanadium source were also stronger than those of the other two kinds of vanadium catalysts. This makes V-OMS-2-V-O exhibit higher catalytic activity. Doping a small amount of V _ (3) can greatly improve the specific surface area of OMS-2. Moreover, the doped V was substituted for Mn~(4 in the form of 5 valence ions, which changed the coordination environment of O around the octahedron of MNO. The activity and reactivity of surface lattice oxygen were increased, and the catalytic activity of OMS-2 in CO oxidation reaction was improved obviously when the amount of V doping was 3. The maximum catalytic activity of V-OMS-2-O is about 50 鈩，

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