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题名: 新型Ce基氧化物NH3-SCR催化剂用于高效去除柴油车尾气中的NOx
作者: 单文坡
学位类别: 博士
答辩日期: 2012
授予单位: 中国科学院研究生院
授予地点: 北京
导师: 贺泓
关键词: 选择性催化还原 ; selective catalytic reduction ; 铈基氧化物催化剂 ; ceria-based catalysts ; NOx催化去除 ; catalytic abatement of NOx ; 柴油车尾气 ; diesel engine exhaust ; 发动机台架测试 ; engine bench test
其他题名: Novel Ceria-based NH3-SCR Catalysts for Efficient NOx Abatement from Diesel Exhaust
中文摘要:       以NH3或尿素为还原剂选择性催化还原NOx,即NH3-SCR,是目前最具应用前景的柴油车尾气NOx控制技术之一。催化剂是整个NH3-SCR系统的核心和关键,而目前现有的催化剂体系都还存在一定的问题。另外,减少催化剂体积是NH3-SCR技术在柴油车上应用需要解决的一个关键问题。因此,开发高效、稳定、环境友好的新型NH3-SCR催化剂体系用于柴油车尾气NOx的去除具有非常重要的意义。 本论文通过简单易行的均匀沉淀法制备出了铈钛氧化物催化剂,显著改善了现有铈钛催化剂体系的低温活性,从而拓宽了操作温度窗口。通过对均匀沉淀法的优化,又成功改善了铈钛催化剂的高温活性,进一步拓宽了其操作温度窗口,并明显改善了其耐高空速性能。通过对催化剂的N2物理吸附、X射线衍射(XRD)、透射电镜(TEM)和扫描电镜-X射线能量色散光谱仪(SEM-EDX)等表征发现,均匀沉淀法制备铈钛氧化物催化剂有利于在TiO2表面形成高度分散的CeO2结构,从而使该催化剂具有优异的NH3-SCR活性。 通过对铈钛氧化物催化剂掺杂过渡金属钨制备出了铈钨钛氧化物催化剂,该催化剂同时提高了铈钛催化剂的低温和高温活性以及N2生成选择性。通过对比钨掺杂对催化剂NO和NH3单独氧化能力的影响,并结合N2物理吸附、XRD、拉曼(Raman)光谱、X射线光电子能谱(XPS)、H2程序升温还原(H2-TPR)和原位漫反射傅立叶变换红外光谱(in situ DRIFTS)等手段,系统分析了钨物种在促进催化剂NH3-SCR活性中的作用。结果表明,钨物种的引入尽管使催化剂的比表面积有所降低,但可以增加表面氧空穴数量、提高催化剂的氧化还原能力,进而增强催化剂低温时氧化NO为NO2的能力,通过“快速SCR”作用促进催化剂的低温活性;另外,钨物种的引入可以同时增加催化剂表面的Brønsted酸性位和Lewis酸性位,进而抑制NH3的非选择性氧化,提高催化剂的高温活性和N2生成选择性。 对铈钨钛氧化物催化剂的研究表明,钨物种在催化剂中可以起到与钛物种相同的提供酸性位等作用,因此采用铈和钨完全替代催化剂中的钛,首次开发出了铈钨氧化物催化剂。该催化剂具有比铈钛氧化物和铈钨钛氧化物催化剂更为优异的NH3-SCR催化性能,即使在500,000 h-1的高空速条件下,铈钨氧化物催化剂仍然可以在250-425 oC的范围内实现100%的NOx转化率,同时具有优异的N2生成选择性、高温热稳定性和抗中毒能力。在相同的评价条件下,该催化剂的催化性能明显优于已经工业化应用的V2O5-WO3/TiO2和Fe-ZSM-5催化剂。 NH3-SCR催化剂在柴油车上的使用环境远比实验室模拟条件下复杂。基于所开发的铈基氧化物催化剂中活性和稳定性最佳的新型铈钨氧化物催化剂,进一步将该催化剂涂覆于堇青石载体上制备了整体催化剂,并在发动机台架上考察了铈钨氧化物催化剂去除实际柴油车尾气NOx的性能。稳态循环(ESC)测试结果表明,通过发动机机内调整使PM、CO和HC原始排放达到国五(欧V)标准后,在不使用DOC等其他辅助后处理系统的条件下,基于该催化剂的SCR后处理系统可使国产重型柴油车NOx排放达到国五(欧V)排放标准,说明该催化剂在柴油车尾气NOx催化净化领域具有非常好的应用前景。
英文摘要:       Selective catalytic reduction of NOx with NH3/urea (NH3-SCR) is one of the most promising after-treatment technologies for NOx abatement from diesel engines. The catalyst plays a key role in NH3-SCR technology. However, there are still some inevitable problems with practical applications of existing NH3-SCR catalysts. In addition, the reduction of SCR catalyst volume is one of the main challenges for diesel vehicles with limited space on-board. There are continuing efforts to develop environmentally-benign NH3-SCR catalysts with excellent activity and stability for controlling the NOx emission from diesel engines. In this study, a Ce-Ti oxide catalyst was prepared by a facile homogeneous precipitation method. Compared with previously reported Ce-Ti oxide catalysts, this catalyst showed remarkably improved low temperature SCR activity and thus broadened operation temperature window. Further optimization of the preparation method resulted in significantly enhanced high temperature activity and further broadened operation temperature window. In addition, the SCR activity under high space velocity conditions was also clearly improved. The N2 physisorption, XRD, TEM, and SEM-EDX results showed that the process of homogenous precipitation is crucial for the production of highly dispersed active CeO2 on TiO2, which is very important for the high SCR activity of the Ce-Ti oxide catalyst. A superior Ce-W-Ti oxide catalyst was prepared by doping W into the Ce-Ti oxide catalyst. The Ce-W-Ti oxide catalyst showed both enhanced low temperature activity and high temperature activity simultaneously, combined with enhanced N2 selectivity, compared with the undoped Ce-Ti oxide catalyst. N2 physisorption, XRD, Raman spectroscopy, XPS, H2-TPR and in situ DRIFTS, etc., together with separate NO oxidation and NH3 oxidation, were used to investigate the effects of W species in the Ce-W-Ti oxide catalyst. The results showed that, although the surface area of the catalyst was decreased to a certain extent, the introduction of W species could increase the amount of surface oxygen vacancies and enhance the redox property of the catalyst, which can benefit the low temperature activity by facilitating the “fast SCR” reaction; the introduction of W species could also simultaneously increase the amount of surface Brønsted and Lewis acid sites, which can enhance both the high temperature activity and N2 selectivity by inhibiting the unselective oxidation of NH3 at high temperatures. Previous studies on Ce-W-Ti oxide catalyst showed that the role of Ti species, such as acidity promotion, could be fulfilled by W species in the catalyst. Therefore, a novel Ce-W oxide catalyst, with a Ce/W molar ratio of 1:1, was developed for the NH3-SCR reaction. The Ce-W oxide catalyst showed much higher SCR activity than the previous Ce-Ti and Ce-W-Ti oxide catalysts. It even exhibited nearly 100% NOx conversion over a wide temperature range from 250 to 425 oC under an extremely high GHSV of 500,000 h-1. The Ce-W oxide catalyst also exhibited excellent N2 selectivity, good stability, and high resistance to poisoning. Under the same test conditions, the Ce-W oxide catalyst showed much better SCR performance than V2O5-WO3/TiO2 and Fe-ZSM-5 catalysts, which have been industrially and commercially applied for NOx abatement from diesel engine exhaust. The application conditions of the NH3-SCR catalyst in real diesel engines are more complex, compared with the test conditions in the laboratory. Therefore, the novel Ce-W oxide catalyst with excellent catalytic performance was washcoated on cylindrical cordierite honeycombs and further tested under practical application conditions on engine benches. European steady state cycle (ESC) test results showed that, after the original PM, CO, and HC emissions of the engine were adjusted by engine modification to meet the standard levels of the Chinese V limit (Euro V limit), the NH3-SCR system based on the Ce-W oxide catalyst could make the NOx emission of the engine fully meet the Chinese V limit (Euro V limit), without the help of any other aftertreatment device, indicating that the Ce-W oxide catalyst is a very promising catalyst for the removal of NOx from diesel engine exhaust.
内容类型: 学位论文
URI标识: http://ir.rcees.ac.cn/handle/311016/35165
Appears in Collections:大气污染控制中心_学位论文

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Recommended Citation:
单文坡. 新型Ce基氧化物NH3-SCR催化剂用于高效去除柴油车尾气中的NOx[D]. 北京. 中国科学院研究生院. 2012.
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