NOx存储还原过程N2O生成机理及抑制方法研究

Lean-burn engines are becoming the preferred scheme to solve the energy consumption and emissions of the conventional engine. The NOx storage and reduction (NSR) technology is the most promising way to reduce the NOx emission from lean-burn engines. However, undesired N2O is found in automotive exhaust. N2O is known to have a significantly high global warming potential and dominant ozone-depleting effect. It is an urgent but unresolved issue that control N2O emissions from automotive exhaust. The studies on the mechanism of N2O in NSR process are in the initial stage due to the complex reaction process and NSR material nonhomogeneity. Based on the dynamic characteristics of NSR process, the in-situ DRIFTS (Nicolet 6700)combined with FTIR (MKS MultiGas2030 ) or FTIR (MKS Multigas 2030) combined with MS (hidden HPR20) techniques are used to study the NSR reaction. The mechanism of N2O formation on Pt-BaO/Al2O3 in NSR process using H2, CO, C3H6 and H2/CO/C3H6 as reducing agent were studied. The influence of some factors ( such as Lean/Rich period, reductant, reaction gas, temperature,H2O, CO2 etc) on the N2O formation was systematic investigated. The formation, activation and transfer of reaction intermediate species were studied by in-situ reaction technology combined with kinetic analysis. The influence of water-gas shift and steam reforming reaction on the NSR process and N2O formation were studied. The mechanism of modification for NSR catalyst was intensively studied to control the N2O formation. A best design solution will be put forward, which would provide the theoretic support for the optimizational design of NSR catalyst.

稀燃技术已成为解决传统发动机能耗与排放问题的首选技术方案，氮氧化物存储还原（NSR）技术有效解决了稀燃条件下氮氧化物脱除的难题，但研究发现NSR过程中有大量温室气体N2O生成。由于NSR反应过程的复杂性，对于NSR过程中的N2O形成机理还处于初级阶段。本课题针对NSR反应的动态特征，建立原位漫反射红外光谱与傅里叶变换红外光谱联用技术及傅里叶变换红外光谱与质谱联用技术对NSR反应过程定性、定量研究的分析测试手段。以PtBaAl模型体系为研究对象，系统研究还原剂种类（H2、CO、C3H6及H2/CO/C3H6）、温度、稀富燃周期、反应气氛等因素对N2O生成机理的影响；采用动力学分析手段研究水煤气变换反应、重整反应等对NSR反应及N2O生成的影响规律，构建NSR催化反应网络。以PtBaAl体系N2O生成机理为指导，阐明NSR催化剂改性机理，抑制N2O生成。为高性能NSR材料的开发提供理论指导。

本课题以Pt-BaO/Al2O3模型体系为研究对象，系统研究了还原剂种类（H2、CO、C3H6及H2/CO/C3H6）、温度、稀富燃周期、反应气氛等因素对N2O生成机理的影响；构建了NSR催化反应网络；以Pt-BaO/Al2O3体系N2O生成机理为指导，对NSR催化材料进行了配方优化。.富燃阶段，N2O主要来自于NO(ad)和N(ad)重新结合产生的。烯燃阶段，N2O产生于气相的NO/O2与NCO/NHx/H等还原性物种之间的反应。反应气氛中的水蒸气不利于N2O在稀燃阶段生成，但是对利于N2O在富燃阶段产生。低温有利于N2O在NSR过程中的产生。N2O的生成与NSR过程的反应网络密切相关。Pd/Al2O3以机械混合的方式掺杂到Pt-BaO/Al2O3能够很大程度上降低N2O生成数量。