負(fù)載型鈣鈦礦催化氧化NO性能及其抗硫機(jī)理研究
發(fā)布時(shí)間：2018-12-16 12:49
【摘要】：由于具有經(jīng)濟(jì)性和環(huán)保性,稀燃發(fā)動(dòng)機(jī)正逐步成為發(fā)動(dòng)機(jī)的主流技術(shù)。但稀燃發(fā)動(dòng)機(jī)尾氣中存在過量O2,傳統(tǒng)三效催化劑無法在此條件下順利還原NOx,導(dǎo)致尾氣中NOx超標(biāo)排放。氮氧化物儲(chǔ)存還原技術(shù)(NSR)因操作方便,還原劑需求量小等優(yōu)點(diǎn)成為最具前景的稀燃NOx控制技術(shù)�，F(xiàn)今NSR催化劑以Pt、Pd、Rh等貴金屬為活性組分,價(jià)格高昂。鈣鈦礦作為一類廉價(jià)金屬化合物,具有良好NSR催化性能。但鈣鈦礦型氧化物比表面積小,在含SO2氣氛下易失活。探究鈣鈦礦型催化劑的硫失活機(jī)理,尋求適宜的改性途徑,提高鈣鈦礦型催化劑的抗硫毒化性能是研制此類非貴金屬高效NSR催化劑要解決的關(guān)鍵問題。本論文首先通過含硫氣氛下的活性測試,結(jié)合各表征手段和吸附脫附實(shí)驗(yàn),研究了NO催化氧化反應(yīng)中,La0.8Ce0.2CoO3鈣鈦礦的硫中毒原因與添加載體CeO2對其抗硫性能的影響及其機(jī)制。結(jié)果表明La0.8Ce0.2CoO3的中毒主要是由于含硫氣氛下催化劑物理化學(xué)性質(zhì)的破壞和穩(wěn)定硫酸鹽的形成。而CeO2載體的加入能作為SO2的優(yōu)先捕獲單元,減緩活性組分的中毒,同時(shí)在NSR反應(yīng)溫度下,CeO2與SO2會(huì)發(fā)生氧化還原反應(yīng),促進(jìn)更多氧空位的產(chǎn)生,從而提高催化劑在含硫氣氛下的活性。隨后論文研究了負(fù)載型La1-xCexCoO3/CeO2(x=0,0.1,0.2,0.3)催化劑中不同Ce摻雜量對催化劑抗硫性能的影響及其機(jī)制。結(jié)果表明高Ce摻雜(x=0.2,0.3)具良好的抗硫性能,而低Ce摻雜(x=0,0.1)抗硫性能差。經(jīng)各表征手段和吸附脫附實(shí)驗(yàn)表明該系列催化劑的中毒主要是含硫氣氛下理化性質(zhì)的改變和SO2對NO2生成的影響。含硫氣體中,Ce摻雜量的增加能提高催化劑理化性質(zhì)的穩(wěn)定性,同時(shí)增加NO2的生成量,提高NO轉(zhuǎn)化率,從而減緩硫中毒速度。論文還研究了不同介孔載體對LaCoO3鈣鈦礦其NO催化氧化活性的影響,其中CeO2、ZrO2和Ce1-xZrxO3能促進(jìn)該體系的催化活性,介孔TiO2、SiO2則相反。載體CeO2的不同制備方法對LaCoO3/CeO2催化劑NO氧化活性影響不大,其中沉淀法制得的催化劑活性最佳,300℃NO轉(zhuǎn)化率達(dá)73.6%,而溶膠凝膠法制備的催化劑低溫活性較好。負(fù)載型LaCoO3/Ce1-xZrxO2中,高鈰少鋯的Ce0.9Zr0.1O3負(fù)載LaCoO3并于600℃焙燒得到的負(fù)載型LaCoO3/Ce0.9Zr0.1O2催化劑具有最高活性。
[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，
本文編號：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，
本文編號：2382376
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