负载型钙钛矿催化氧化NO性能及其抗硫机理研究
发布时间：2018-12-16 12:49
【摘要】：由于具有经济性和环保性,稀燃发动机正逐步成为发动机的主流技术。但稀燃发动机尾气中存在过量O2,传统三效催化剂无法在此条件下顺利还原NOx,导致尾气中NOx超标排放。氮氧化物储存还原技术(NSR)因操作方便,还原剂需求量小等优点成为最具前景的稀燃NOx控制技术。现今NSR催化剂以Pt、Pd、Rh等贵金属为活性组分,价格高昂。钙钛矿作为一类廉价金属化合物,具有良好NSR催化性能。但钙钛矿型氧化物比表面积小,在含SO2气氛下易失活。探究钙钛矿型催化剂的硫失活机理,寻求适宜的改性途径,提高钙钛矿型催化剂的抗硫毒化性能是研制此类非贵金属高效NSR催化剂要解决的关键问题。本论文首先通过含硫气氛下的活性测试,结合各表征手段和吸附脱附实验,研究了NO催化氧化反应中,La0.8Ce0.2CoO3钙钛矿的硫中毒原因与添加载体CeO2对其抗硫性能的影响及其机制。结果表明La0.8Ce0.2CoO3的中毒主要是由于含硫气氛下催化剂物理化学性质的破坏和稳定硫酸盐的形成。而CeO2载体的加入能作为SO2的优先捕获单元,减缓活性组分的中毒,同时在NSR反应温度下,CeO2与SO2会发生氧化还原反应,促进更多氧空位的产生,从而提高催化剂在含硫气氛下的活性。随后论文研究了负载型La1-xCexCoO3/CeO2(x=0,0.1,0.2,0.3)催化剂中不同Ce掺杂量对催化剂抗硫性能的影响及其机制。结果表明高Ce掺杂(x=0.2,0.3)具良好的抗硫性能,而低Ce掺杂(x=0,0.1)抗硫性能差。经各表征手段和吸附脱附实验表明该系列催化剂的中毒主要是含硫气氛下理化性质的改变和SO2对NO2生成的影响。含硫气体中,Ce掺杂量的增加能提高催化剂理化性质的稳定性,同时增加NO2的生成量,提高NO转化率,从而减缓硫中毒速度。论文还研究了不同介孔载体对LaCoO3钙钛矿其NO催化氧化活性的影响,其中CeO2、ZrO2和Ce1-xZrxO3能促进该体系的催化活性,介孔TiO2、SiO2则相反。载体CeO2的不同制备方法对LaCoO3/CeO2催化剂NO氧化活性影响不大,其中沉淀法制得的催化剂活性最佳,300℃NO转化率达73.6%,而溶胶凝胶法制备的催化剂低温活性较好。负载型LaCoO3/Ce1-xZrxO2中,高铈少锆的Ce0.9Zr0.1O3负载LaCoO3并于600℃焙烧得到的负载型LaCoO3/Ce0.9Zr0.1O2催化剂具有最高活性。
[Abstract]:Because of its economy and environmental protection, lean combustion engine is gradually becoming the mainstream technology of engine. However, there is excess O _ 2 in the tail gas of lean combustion engine, and the traditional three-way catalyst can not reduce NOx, smoothly under this condition, which leads to the NOx emission exceeding the standard in the tail gas. Nitrogen oxide storage and reduction technology (NSR) has become the most promising lean burning NOx control technology because of its advantages such as easy operation and low demand for reductant. At present, the NSR catalyst is expensive with Pt,Pd,Rh and other precious metals as active components. As a kind of cheap metal compound, perovskite has good NSR catalytic performance. However, perovskite oxides have small specific surface area and are easily deactivated in SO2-containing atmosphere. To explore the mechanism of sulfur deactivation of perovskite catalysts, to find suitable ways of modification and to improve the sulfur resistance of perovskite catalysts are the key problems to be solved in the development of this kind of non-noble metal efficient NSR catalysts. In this paper, the catalytic oxidation of NO was studied by means of various characterization methods and adsorption and desorption experiments. The reason of sulfur poisoning in La0.8Ce0.2CoO3 perovskite and the effect of adding carrier CeO2 on its sulfur resistance and its mechanism. The results showed that the poisoning of La0.8Ce0.2CoO3 was mainly due to the destruction of the physical and chemical properties of the catalyst and the formation of stable sulfate in the sulfur-containing atmosphere. The addition of CeO2 carrier can be used as the priority trapping unit of SO2, which can reduce the poisoning of active components. At the same time, at the reaction temperature of NSR, the redox reaction between CeO2 and SO2 will take place, which will promote the production of more oxygen vacancies. Thus, the activity of the catalyst in sulfur-containing atmosphere was improved. Then the influence of different Ce doping amount on the sulfur resistance of supported La1-xCexCoO3/CeO2 catalyst was studied. The results show that high Ce doping (XG 0.2C0. 3) has good sulfur resistance, while low Ce doping (XC0. 1) has poor sulfur resistance. The results of characterization and adsorption and desorption experiments showed that the poisoning of this series of catalysts was mainly due to the change of physical and chemical properties in sulfur-containing atmosphere and the effect of SO2 on the formation of NO2. In the sulfur-containing gas, the increase of Ce doping can improve the stability of the catalyst's physical and chemical properties, at the same time, increase the amount of NO2, increase the conversion of NO, so as to slow down the rate of sulfur poisoning. The effect of different mesoporous carriers on the catalytic oxidation activity of LaCoO3 perovskite was also studied. CeO2,ZrO2 and Ce1-xZrxO3 could promote the catalytic activity of the system, whereas the mesoporous TiO2,SiO2 could promote the catalytic activity of the system. Different preparation methods of CeO2 have little effect on the oxidation activity of LaCoO3/CeO2 catalyst. The catalyst prepared by precipitation method has the best activity, the conversion of NO at 300 鈩，
本文编号：2382376
[Abstract]:Because of its economy and environmental protection, lean combustion engine is gradually becoming the mainstream technology of engine. However, there is excess O _ 2 in the tail gas of lean combustion engine, and the traditional three-way catalyst can not reduce NOx, smoothly under this condition, which leads to the NOx emission exceeding the standard in the tail gas. Nitrogen oxide storage and reduction technology (NSR) has become the most promising lean burning NOx control technology because of its advantages such as easy operation and low demand for reductant. At present, the NSR catalyst is expensive with Pt,Pd,Rh and other precious metals as active components. As a kind of cheap metal compound, perovskite has good NSR catalytic performance. However, perovskite oxides have small specific surface area and are easily deactivated in SO2-containing atmosphere. To explore the mechanism of sulfur deactivation of perovskite catalysts, to find suitable ways of modification and to improve the sulfur resistance of perovskite catalysts are the key problems to be solved in the development of this kind of non-noble metal efficient NSR catalysts. In this paper, the catalytic oxidation of NO was studied by means of various characterization methods and adsorption and desorption experiments. The reason of sulfur poisoning in La0.8Ce0.2CoO3 perovskite and the effect of adding carrier CeO2 on its sulfur resistance and its mechanism. The results showed that the poisoning of La0.8Ce0.2CoO3 was mainly due to the destruction of the physical and chemical properties of the catalyst and the formation of stable sulfate in the sulfur-containing atmosphere. The addition of CeO2 carrier can be used as the priority trapping unit of SO2, which can reduce the poisoning of active components. At the same time, at the reaction temperature of NSR, the redox reaction between CeO2 and SO2 will take place, which will promote the production of more oxygen vacancies. Thus, the activity of the catalyst in sulfur-containing atmosphere was improved. Then the influence of different Ce doping amount on the sulfur resistance of supported La1-xCexCoO3/CeO2 catalyst was studied. The results show that high Ce doping (XG 0.2C0. 3) has good sulfur resistance, while low Ce doping (XC0. 1) has poor sulfur resistance. The results of characterization and adsorption and desorption experiments showed that the poisoning of this series of catalysts was mainly due to the change of physical and chemical properties in sulfur-containing atmosphere and the effect of SO2 on the formation of NO2. In the sulfur-containing gas, the increase of Ce doping can improve the stability of the catalyst's physical and chemical properties, at the same time, increase the amount of NO2, increase the conversion of NO, so as to slow down the rate of sulfur poisoning. The effect of different mesoporous carriers on the catalytic oxidation activity of LaCoO3 perovskite was also studied. CeO2,ZrO2 and Ce1-xZrxO3 could promote the catalytic activity of the system, whereas the mesoporous TiO2,SiO2 could promote the catalytic activity of the system. Different preparation methods of CeO2 have little effect on the oxidation activity of LaCoO3/CeO2 catalyst. The catalyst prepared by precipitation method has the best activity, the conversion of NO at 300 鈩，
本文编号：2382376
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