正十二烷模拟车载燃油催化重整耦合选择性还原NOx研究
文献类型：学位论文
| 作者 | 赵娇娇 |
| 学位类别 | 硕士 |
| 答辩日期 | 2013-05 |
| 授予单位 | 中国科学院研究生院 |
| 授予地点 | 北京 |
| 导师 | 余运波 |
| 关键词 | 燃油重整 镍基催化剂 氮氧化物 选择性催化还原 银/氧化铝 fuel reforming Ni-based catalysts nitrogen oxides selective catalytic reduction silver/alumina |
| 其他题名 | Study of n-C12H26 catalytic reforming coupled with selective catalytic reduction of NOx over Ag/Al2O3 |
| 学位专业 | 环境工程 |
| 中文摘要 | 大气中的氮氧化物（NOx，主要为NO和NO2）是酸雨、光化学烟雾和灰霾等环境污染现象发生的重要前体污染物，而柴油车尾气排放已成为NOx污染的重要来源。柴油车尾气中氧气绝对过量的特征加大了将NOx还原为N2的难度，使得通过还原剂添加选择性催化还原NOx（SCR）技术成为一种的可行技术路线。以车载燃油为还原剂来源的碳氢选择性催化还原NOx技术（HC-SCR）是柴油车尾气后处理的理想目标。本论文以正十二烷（n-C12H26）模拟车载燃油，利用催化重整技术同时制备小分子碳氢化合物（HC）和H2，为后置的银/氧化铝（Ag/Al2O3）这一具有实际应用前景的HC-SCR催化剂同时提供NOx还原所需的还原剂和反应助剂，以期弥补柴油直接为还原剂时NOx净化效率低和稳定性差的缺陷。 分别以La2O2CO3、CeO2、ZrO2和Al2O3为载体，浸渍法负载5 wt% Ni作为正十二烷重整反应的催化剂。研究表明，随着重整催化剂氧化还原性能的增强，重整反应产物中H2浓度增加，可参与SCR反应的HCs含量随之减少。H2的形成及其浓度的增加导致后置SCR催化剂上NOx净化活性温度窗口向低温移动，而HCs含量的减少致使NOx最高转化率降低。Ni/ZrO2 + Ag/Al2O3耦合催化体系中因H2及HCs浓度符合SCR反应所需的最佳比例，在柴油车的典型排气温度范围内表现出良好的NOx净化能力。 采用尿素均匀沉淀法制备了LaxCe(1-x)O2-δ （x为La/(La + Ce)的摩尔比例，x = 0.1、0.3、0.5、0.7）复合型氧化物。XRD、Raman表征结果表明，La3+离子进入了CeO2晶格并与其形成了La-Ce固溶体。H2-TPR结果显示，La/Ce比例的调变显著影响了Ni/LaxCe(1-x)O2-δ重整催化剂的氧化还原能力，使其呈现出不同的抗积碳能力。与Ni/La2O2CO3 (或Ni/CeO2) + Ag/Al2O3相比，Ni/La0.3Ce0.7O2-δ催化剂参与耦合反应时，NOx净化活性温度窗口及其最高转化率显著变宽、增大；La/Ce比例、Ni负载量优化结果显示，5% Ni/La0.3Ce0.7O2-δ + Ag/Al2O3组合体系的NOx净化效率与抗积碳能力最优。 以La0.3Ce0.7O2-δ为载体连续浸渍负载Ni和Rh制备双活性组分重整催化剂，贵金属Rh的存在明显增强了重整催化剂的低温氧化还原性能，从而对重整-SCR体系净化NOx的低温活性与温度窗口产生明显影响，并增强了催化剂在重整反应中的稳定性；0.25% Rh-5% Ni/La0.3Ce0.7O2-δ + Ag/Al2O3耦合体系净化NOx的低温活性最高，活性温度窗口最宽。 |
| 英文摘要 | Oxides of nitrogen (NOx, mainly NO and NO2) in atmosphere are key precursory pollutants induced the formation of acid rain, photochemical smog, and haze, while the diesel exhaust emissions has become an important source of NOx pollution. The presence of excess oxygen in diesel exhaust provides severe condition for the reduction of NOx to N2. In this case, selective catalytic reduction (SCR) of NOx is a desired pathway. Using on-board fuel as the only source of reducing agent for NOx purification is an ideal HC-SCR system for diesel engine exhaust aftertreatment. Considering the defects of low NOx removal efficiency and catalyst deactivation when on-board fuel is used directly as reductant, herein, a coupled reaction system combined catalytic reforming with SCR was set up. Fuel reforming catalysts were synthesized and applied to simultaneous generation of small molecular HCs and H2 from n-C12H26 (as a representative of on-board fuel). The above reforming products further served as reductants and promoters for the SCR of NOx over silver/alumina catalyst (Ag/Al2O3), which has been identified as a candidate for commercial application in diesel engine exhaust purification. Using La2O2CO3, CeO2, ZrO2 and Al2O3 as supports, 5 wt% Ni-based catalysts were synthesized by an impregnation method for catalytic reforming of n-C12H26. It was shown that, an increase in the redox performance of Ni-based catalysts enhanced the H2 production from fuel reforming, while it decreased the amount of HCs available for further SCR reaction. Therefore, the temperature window of NOx conversion shifted to lower temperatures as H2 concentration increased, at the expense of the maximum NOx conversion due to decreased HCs concentration. An optimal concentration of both H2 and HCs was achieved on the Ni/ZrO2 + Ag/Al2O3 dual catalyst system, which exhibited high activity for NOx purification at typical diesel exhaust temperatures. A series of LaxCe(1-x)O2-δ (x = 0.1, 0.3, 0.5, 0.7) composite oxides were synthesized by a urea homogeneous precipitation method. Results of XRD and Raman characterization indicated that La3+ incorporated into the CeO2 crystal lattice to form La-Ce solid solution. H2-TPR results displayed that tuning the La/Ce ratio resulted in obvious changes in redox property, thus affected the resistance to carbon deposition of Ni/LaxCe(1-x)O2-δ catalysts. Compared with Ni/La2O2CO3 (or Ni/CeO2) + Ag/Al2O3 coupled system, the Ni/La0.3Ce0.7O2-δ + Ag/Al2O3 exhibits a wider temperature window for NOx removal and the maximum NOx conversion was dramaticaly improved. Among the tested catalyst with varied La/Ce ratio and Ni loading, 5% Ni/La0.3Ce0.7O2-δ + 4% Ag/Al2O3 coupled system exhibited an outstanding NOx purification efficiency and the best carbon deposition resistance. A Rh-Ni bimetallic reforming catalyst supported on La0.3Ce0.7O2-δ was prepared by a continuous impregnation method. The presence of Rh promoted the reductibility of Ni/La0.3Ce0.7O2-δ at low temperatures, significantly changing NOx conversion and activity temperature window and enhanced the activity stability during catalytic reforming reaction. Over the tested fuel reforming-SCR coupled systems, 0.25% Rh-5% Ni/La0.3Ce0.7O2-δ + 4% Ag/Al2O3 exhibited the highest NOx conversion at low temperature and the widest activity temperature window. |
| 公开日期 | 2014-10-28 |
| 源URL | [http://ir.rcees.ac.cn/handle/311016/7705]  |
| 专题 | 生态环境研究中心_大气环境科学实验室 |
| 推荐引用方式 GB/T 7714 | 赵娇娇. 正十二烷模拟车载燃油催化重整耦合选择性还原NOx研究[D]. 北京. 中国科学院研究生院. 2013. |
入库方式： OAI收割
来源：生态环境研究中心
浏览0
下载0
收藏0
其他版本
除非特别说明，本系统中所有内容都受版权保护，并保留所有权利。