二氧化钛纳米带负载Au-Ag纳米催化剂的制备及其性能研究

发布时间：2018-08-06 14:19

【摘要】：CO是大气中的主要污染物之一,空气中CO的存在对环境和人类的身体健康都存在很大的危害。在其它的工业生产中,如燃料电池的使用,CO会造成Pt电极中毒,影响其使用效率。CO的氧化反应是去除CO的一种有效途径,CO的氧化尤其是低温条件下的氧化反应,具有很高的实用价值,可以应用于室内气体净化,防毒面具、CO气体传感器等方面。而且由于CO反应较为简单可以作为探针反应来探究催化反应的机理,因此CO低温催化氧化反应具有非常重要的实用价值和理论研究意义。Au基纳米催化剂是CO催化氧化中研究和应用最为广泛的一类催化剂。双金属催化剂由于第二种金属加入而存在的协同作用促使其具有高于单金属催化剂的活性和稳定性,因此其合成和应用研究已成为催化研究领域的热点之一。一维TiO2纳米带采用简单的水热法合成,合成过程中没有使用其他大分子表面活性剂,具有表面干净平滑,缺陷位分布均匀的特点,是一种理想的催化剂载体。并且由于TiO2纳米带的一维类纤维结构,可以将其组装为整体多孔结构纳米纸催化剂。此外,光沉积的方法由于操作简单、成本较低、绿色无污染的特点也是制备负载型催化剂的一种常用方法。本论文采用光沉积法以及两步连续光沉积法,分别在将Au以及Au-Ag纳米颗粒负载于一维纳米材料TiO2纳米带表面,制备Au/TiO2-NB和Au-Ag/TiO2-NB纳米结构,并将其组装为整体多孔结构纳米纸催化剂应用于CO低温催化氧化反应,具体研究内容如下：1.采用连续两步光沉积法制备了负载于TiO2纳米带的双金属Au-Ag/TiO2-NB纳米催化剂,并将其组装为整体多孔纳米纸结构。采用SEM、TEM、XRD、ICP. UV-Vis光吸收和XPS等测试手段,分别表征了纳米催化剂颗粒的形貌、组成和结构。由SEM图像可以看出纳米纸呈现三维交叉贯穿的结构,具有较大的孔隙率和比表面积。由TEM图可以看出,金属纳米颗粒均匀地分布于TiO2纳米带表面,其粒径呈双峰分布,其中小颗粒粒径约为2 nm。根据UV-Vis光吸收和XPS分析可知,所制备的双金属Au-Ag/TiO2-NB纳米结构中的金属颗粒为表面富集氧化银的合金结构。2.将制备的双金属Au-Ag/TiO2-NB纳米催化剂应用于CO的低温催化氧化反应,分别研究了制备过程中先驱体溶液的pH值、预处理条件和制备方法对催化剂活性的影响。结果表明：当先驱体溶液pH值为10时,单金属Au/TiO2-NB纳米催化剂活性最高,这是因为此条件下制备的Au颗粒较小,而且由于AuCl4-离子水解程度较高,Cl-残留量较低,因此其催化活性较高。其次,采用先沉积Au后沉积Ag的连续两步光沉积方法制备的催化剂,避免了先沉积Ag后沉积Au和原位置换方法制备过程中AgCl的生成个而具有较高的催化活性。由于双金属催化剂的活性受到结构及组成的影响,所以系统的探讨了Au/Ag比例及预处理条件对催化活性的影响,当Au/Ag比例为1：0.8,经过400℃还原预处理后活性最高。由于低温下CO的催化氧化反应中Au基纳米催化剂出现失活现象,因此采用失活-重生循环反应的方法探讨了双金属Au-Ag/TiO2-NB纳米催化剂失活的原因。3.Au纳米催化剂活性受到粒径及空间分布的影响,当纳米颗粒粒径较小空间分布密度较小时,容易发生团聚现象而导致催化剂失活现象的产生,因此制备具有较小粒径和空间分布均匀的纳米催化剂具有很高的实用价值。本文通过系统的调控光沉积过程中的光沉积时间和前驱体浓度的方法制备了粒径和空间分布可控且具有高抗烧结性能的Au基纳米催化剂。当前驱体为1 mL 0.025 mol·L-1的HAuCl4溶液于400 w氙灯下光照10 s,催化剂纳米颗粒粒径为2.5 nm,可将反应条件下的CO完全转化,当前驱体溶液用量下降至0.1 mL时,Au纳米颗粒的粒径尺寸仅为1.4 nm,尽管负载量较低(0.056 wt.%)但对CO的催化氧化反应依然具有良好的催化活性。
[Abstract]:CO is one of the main pollutants in the atmosphere. The presence of CO in the air is very harmful to the environment and human health. In other industrial production, such as the use of fuel cells, CO will cause Pt electrode poisoning. The oxidation reaction of.CO, which affects the use efficiency, is an effective way to remove CO, and the oxidation of CO, especially the low temperature strip, is an effective way. The oxidation reaction under the component is of high practical value. It can be applied to indoor gas purification, gas mask, CO gas sensor and so on. And because the reaction of CO can be used as a probe reaction to explore the mechanism of catalytic reaction, the catalytic oxidation reaction of CO at low temperature has very important practical value and theoretical significance.A. U based nano catalysts are one of the most widely used catalysts in the catalytic oxidation of CO. The synergistic effect of bimetallic catalysts because of the addition of second metals makes it higher than the activity and stability of the single metal catalysts. Therefore, the synthesis and application of bimetallic catalysts have become one of the hotspots in the field of catalytic research. One dimension TiO2 The nanometers are synthesized by a simple hydrothermal method. There is no use of other macromolecular surfactants in the synthesis process. It has the characteristics of clean surface and smooth surface and uniform distribution of defects. It is an ideal catalyst carrier. And because of the one-dimensional fiber structure of TiO2 nanometers, it can be assembled into a whole porous structure nanoscale catalyst. In addition, the method of light deposition is a common method for the preparation of supported catalyst because of its simple operation, low cost and green non pollution. In this paper, Au and Au-Ag nanoparticles were loaded on the surface of TiO2 nanomaterials of one dimension nanomaterial, respectively, and the Au/TiO2-NB and Au-Ag/Ti were prepared by the method of light deposition and two step continuous photo deposition. O2-NB nanostructures were assembled into a holistic porous structure nanoscale catalyst for CO catalytic oxidation at low temperature. The specific contents of the study are as follows: 1. a double metal Au-Ag/TiO2-NB nano catalyst loaded with TiO2 nanoribbons was prepared by continuous two step photodeposition and assembled into a holistic porous nanoscale structure. SEM, TEM, The morphology, composition and structure of the nanoparticles are characterized by XRD, ICP. UV-Vis optical absorption and XPS, respectively. From the SEM image, it can be seen that the nanoscale paper presents a three dimensional cross penetration structure with a larger porosity and specific surface area. As can be seen from the TEM diagram, the metal nanoparticles are evenly distributed on the surface of the TiO2 nanoscale and its particles. The diameter is Shuangfeng distribution. The small particle size is about 2 nm., according to UV-Vis light absorption and XPS analysis, the metal particles in the bimetal Au-Ag/TiO2-NB nanostructures are the alloy structure of the surface enriched with silver oxide. The prepared bimetallic Au-Ag/TiO2-NB nanoscale catalyst should be used for the low temperature catalytic oxidation reaction of CO, respectively. The effect of pH value of precursor solution, pretreatment conditions and preparation methods on the activity of the catalyst during the preparation process showed that when the pH value of the precursor solution was 10, the activity of the single metal Au/TiO2-NB nano catalyst was the highest, which was due to the smaller Au particles prepared under this condition, and the Cl- residue was higher because of the high degree of hydrolysis of the AuCl4- ions. The catalyst has a higher catalytic activity. Secondly, the catalyst prepared by the two step photodeposition method, which deposited the Au before deposition of Ag, avoids the formation of AgCl in the preparation of Au and in situ replacement after the deposition of Ag first and has higher catalytic activity. Therefore, the effect of Au/Ag ratio and preconditioning conditions on catalytic activity was systematically investigated. When the proportion of Au/Ag was 1:0.8, the activity was highest after reduction of 400 degrees C. Due to the deactivation of Au based nano catalyst in the catalytic oxidation of CO at low temperature, the bimetallic Au-Ag/TiO was discussed by the method of inactivation rebirth reaction. The cause of 2-NB nano catalyst deactivation is that the activity of.3.Au nano catalyst is affected by the particle size and spatial distribution. When the small particle size distribution is small, the agglomeration phenomenon is easy to occur, which leads to the deactivation of the catalyst. Therefore, the preparation of nano catalyst with small particle size and uniform spatial distribution is very high. In this paper, the Au based nanoscale catalyst with controllable particle size and space distribution and high sintering resistance is prepared by systematic regulation of the light deposition time and precursor concentration in the process of photomivating. The current drive body is 1 mL 0.025 mol. L-1 HAuCl4 solution under 400 W xenon lamp, 10 s, and the particle size of catalyst nanoparticles For 2.5 nm, the CO can be completely converted under the reaction condition. The size of Au nanoparticles is only 1.4 nm when the current volume of the flooding solution is reduced to 0.1 mL. Although the load is low (0.056 wt.%), the catalytic oxidation reaction of CO still has good catalytic activity.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O643.36;TB383.1

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