铈锆氧化物 用于NH3选择性催化还原去除柴油车尾气中的 NO x
文献类型：学位论文
| 作者 | 丁世鹏 |
| 学位类别 | 硕士 |
| 答辩日期 | 2015-05 |
| 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、柴油车尾气、氮氧化物去除、铈锆氧化物催化剂、热稳定性,selectivity catalytic reduction, diesel engine exhaust, the removal of NOx, CeZrOx oxide catalysts, thermal stability |
| 其他题名 | Ce-Zr Oxides for the Selective Catalytic Reduction of NOx from Diesel Exhaust with NH3 |
| 学位专业 | 环境工程 |
| 中文摘要 | 柴油车排放的污染物氮氧化物(NOx)是造成大气污染的主要污染物之一。NH3选择性催化还原NOx，即 NH3-SCR技术是当前净化富氧尾气中 NOx的主流技术之一。广泛用于固定源脱硝的 V2O5-WO3/TiO2体系，在用于柴油车尾气控制仍然存在许多问题，例如活性组分钒具有较强的毒性，活性温度窗口较窄，高温时 SO2氧化为 SO3等。因此，开发新型高效的SCR催化剂以取代传统的钒基催化剂具有非常重要的意义。铈锆氧化物同时具有 CeO2的氧化还原能力以及ZrO2的高热稳定性，有望应用于柴油车尾气 NOx净化过程。 本论文首先考察了各组分含量、Ce前驱体和沉淀剂类型对 CeMoZrOx催化剂 NH3-SCR活性的影响，并研究了CeMoZrOx的抗 H2O/SO2中毒能力以及热稳定性。以硝酸铈为前驱体，以尿素为沉淀剂，采用均匀沉淀法制备的 CeMo0.5Zr2Ox催化剂(各元素摩尔比为 Ce:Mo:Zr=1:0.5:2)具有最高的 SCR活性，同时在250oC以上具有较强的抗 H2O/SO2中毒以及热稳定性。N2物理吸附、X射线衍射(XRD)、可见拉曼(Visible Raman)、H2程序升温还原(H2-TPR)、X射线光电子能谱(XPS)以及原位漫反射傅里叶变换红外光谱(in situ DRIFTS)等多种表征结果表明，以硝酸铈为前驱体，以尿素为沉淀剂制备的 CeMo0.5Zr2Ox催化剂具有较大的表面积、强的氧化还原能力和较为丰富的表面 Ce物种，同时对反应物种NH3和NOx具有3+较强的吸附能力，因而具有较强的NH3-SCR性能。 CeMo0.5Zr2Ox催化剂虽然具有较高的NH3-SCR性能，但是其高温N2选择性较差，在450oC时N2生成选择性仅为60%。文献表明，Nb可以显著提高CeO2的 SCR活性和 N2选择性，因此又制备了CeNbZrOx催化剂。结果显示，Nb的添加显著提高了CeZrOx在NH3-SCR反应中的 NOx转化率和 N2生成选择性。性能最优的 CeNb3.0Zr2Ox催化剂的活性和选择性均高于CeMo0.5Zr2Ox催化剂，同时在中高温段具有优异的抗 H2O/SO2中毒能力。Nb的添加显著提高了催化剂的表面积，使催化剂由晶体结构转变为无定形结构，同时提高了氧化还原能力。另一方面，Nb的添加增加了催化剂表面酸性位点的数量，增强了表面酸性位的强度，提高了催化剂表面吸附的 NH3和NO3-等物种的反应活性。eNb3.0Zr2Ox相对于目前报道的氧化物催化剂，具有极佳的水热稳定性，在经 800oC高温水热老化后，仍拥有大量的酸性位点和较强的氧化还原能力。 |
| 英文摘要 | Nitrogen oxides (NOx) are considered to be one of the major sources of environmental pollution. Selective catalytic reduction of NOx with NH3 (NH3-SCR) is one of the main technologies to eliminate NOx from oxygen-rich exhaust. Although V2O5-WO3/TiO2 catalysts are widely used for the removal of NOx from stationary sources, some problems remain when they are applied in diesel emission control, including the toxicity of vanadium pentoxide, narrow operation temperature window and high conversion of SO2 to SO3 at high temperatures. Therefore, it is desirable to develop novel SCR catalysts able to substitute for the conventional V-based catalysts. Ce-Zr mixed oxide, which combines the high redox ability of CeO2 with the highly refractory nature of ZrO2, can be used as a catalyst or support for the NH3-SCR of NOx from diesel engine exhaust. The CeMo0.5Zr2Ox catalyst showed superior NH3-SCR performance, however, the N2 selectivity was about 60% at 450oC and should be improved. It was reported that the addition of Nb to CeO2 can improve the SCR activity and N2 selectivity greatly. The influence of Nb addition on the CeZr2Ox was also studied systematically. The NOx conversion and N2 selectivity over CeZr2Ox were significantly improved by addition of Nb. The NOx conversion and N2 selectivity over the optimal CeNb3.0Zr2Ox catalyst were higher than those over CeMo0.5Zr2Ox catalyst. Furthermore, the CeNb3.0Zr2Ox catalyst showed high resistance to SO2/H2O poisoning. The introduction of Nb to CeZr2Ox not only resulted in high surface area and strong redox ability, but also promoted the adsorption and activation of NH3 and enhanced the reactivity of adsorbed nitrate together with NH3 species. The CeNb3.0Zr2Ox catalyst showed superior hydrothermal stability compared to other reported oxide catalysts. In addition, the CeNb3.0Zr2Ox catalyst still possessed abundant acid sites and high redox ability after hydrothermal aging below 800 °C. |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/34357]  |
| 专题 | 生态环境研究中心_大气污染控制中心 |
| 推荐引用方式 GB/T 7714 | 丁世鹏. 铈锆氧化物 用于NH3选择性催化还原去除柴油车尾气中的 NO x[D]. 北京. 中国科学院研究生院. 2015. |
入库方式： OAI收割
来源：生态环境研究中心
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