基于沸石内络合反应的阻抗型氨气传感器研究

In order to control and significantly reduce NOx emission for commercial vehicles, an SCR (Selective Catalytic Reduction) exhaust gas after-treatment system, which uses ammonia as a reductant, is introduced to decompose NOx. A gas sensor is required to monitor and detect the concentration of ammonia in the SCR system. Several attempts for ammonia sensor in the SCR system have been reported in the literatures, but one general disadvantage with respect to the cross-sensitivity hinder the sensors for practical application. This project propose an impedimetric ammonia sensor based on intrazeolitic complex reaction, whose impedance response is depend on the interaction between ammonia and intrazeolitic metal cations. This novel gas-sensing mechanism could effectively avoid the interference from the others in the SCR system. Firstly, to define the temperature range that the intrazeolitic complex reaction become reversibility, we would study the relationship between intrazeolitic complex reaction and temperature based on different metal cations and zeolite. Secondly, focused research addresses the question: how does the complex reaction influence the ionic conductivity of zeolite? The influence mechanism could be confirmed by understanding the correlation between the different zeolite, metal cations and their gas-sensing response to ammonia. The gas-sensing model based on the intrazeolitic complex reaction will also be presented by analyzing the experimental results. Finally, the sensor is going to be tested in a simulated SCR environment. Moreover, expected problem relate to the interference of water is going to be solved by two methods: zeolite with high Si/Al ratio is prepared to enhance its hydrophobicity; measuring parameters is optimized to decrease the influence of water based on the analysis the components of impedance spectroscopy of sensors. In summary, the project will make a unique contribution to develop and research ammonia sensor with high sensitivity and selectivity in the SCR system.

对汽车尾气中氮氧化合物（NOx）排放的控制，采用的是加装选择性催化还原（SCR）系统来分解NOx。SCR系统中，还原剂氨气的浓度需要准确的检测和监控。但在对SCR氨气传感器的研究中，传感器的选择性始终未能满足应用要求。本项目提出了一种基于沸石内络合反应的阻抗型氨气传感器。通过氨气与沸石内金属阳离子之间的络合反应，引起沸石阻抗的变化。这种新的气敏机理可以使传感器在SCR系统中有效地避免其它气体的干扰。首先，通过研究沸石内络合反应与温度之间的关系，界定该反应随氨气浓度可逆变化的温度范围。其次，重点研究络合反应对沸石离子电导的作用机理，揭示沸石类型，阳离子种类等与气敏响应之间的关联，完善相关理论并建立气敏机理模型。最后，SCR模拟环境下，测试传感器的气敏性能。此外，为减小水对传感器的干扰，通过制备高硅铝比沸石以提高疏水性，或解析阻抗谱而优化测量参数来降低水的影响。本项目的实施将研制出具有高灵敏度和选择性的SCR氨气传感器。

汽车尾气中的NOx污染物是通过SCR催化系统进行分解，氨气作为还原剂被注入到SCR系统中，因此在SCR系统中需要传感器对氨气含量进行检测。由于汽车尾气中气体成分复杂，项目组采用沸石作为敏感材料，利用氨气吸附改变沸石离子电导的特性，研制具有高选择性的氨气阻抗型传感器。项目主要研究了：1、不同沸石对氨气的气敏响应，工作温度区间，灵敏度，响应恢复时间等；2、沸石中氨络合物对阳离子跃迁的作用机理，阳离子跃迁能量，氨气吸附对跃迁活化能的影响，及其对温度的依赖性。实验结果表明沸石中采用不同的离子，传感器的工作温度可以在200~350 °C之间调节，由于氨气与沸石中电导离子以共价键结合，它们之间的吸引力会减弱离子和沸石骨架之间的吸引力，从而减小了离子电导活化能。除了以上研究内容，项目组拓展关于电化学传感器，电子鼻及其相关的应用研究。1、关于氧化钯电极的气敏反应机理研究，我们提出了电偶层理论解释氧化钯电极和电解质界面的气敏响应。区别于经典混合电位理论，气体在氧化钯表面的催化反应，引起界面处电荷密度的变化，从而使电偶层电位随气体浓度的变化。2、混合VOCs气体的浓度预测算法研究，为了可以定量识别混合VOCs气体，我们提出了采用先按气体浓度分类，在按不同分类进行回归运算。通过这两个步骤的运算，对四种VOCs混合气体的分类误差率小于5%。3、电子鼻在人体气味分类识别中的应用研究，我们采用电子鼻对人体气味的特异性进行识别分析，电子鼻由6个传感器组成阵列，并且设计了信号采集和传输电路，对8个志愿者的人体气味进行测试，根据传感器信号动态变化过程，我们提出了对比响应作为特征向量，经过PCA降维和K-means分类处理，最高正确率可达91%。在本项目的资助下，发表学术文章12篇，申请发明专利5项，培养博士后1名，博士研究生1名，硕士研究生4名。多次参加国内外学术会议进行交流，并与多个课题组进行合作。基于本项目研究成果承接横向项目1项。