Mechanistic Understanding of Cu-CHA Catalyst as Sensor for Direct NH3-SCR Monitoring: The Role of Cu Mobility
Mechanistic Understanding of Cu-CHA Catalyst as Sensor for Direct NH3-SCR Monitoring: The Role of Cu Mobility
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Cu-CHA 催化剂作为直接 NH3-SCR 监测传感器的机理理解：铜迁移率的作用
DOI：
10.1021/acsami.8b22104
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发表时间：
2019-02-27
影响因子：
9.5
通讯作者：
Simon, Ulrich
中科院分区：
文献类型：
--
作者：
Chen, Peirong;Rizzotto, Valentina;Simon, Ulrich
直接利用催化剂作为传感器的概念对于许多催化应用，特别是对于汽车排放的催化减排，在根本上和技术上是有吸引力的。在这里，我们探讨了微孔铜交换菱沸石（Cu-CHA，包括Cu-SSZ-13和Cu-SAPO-34）沸石催化剂，这是商业上使用的选择性催化还原汽车氮氧化物排放的氨（NH3-SCR），作为阻抗传感器元件直接监测NH3-SCR过程的潜力。商业Cu-SSZ-13和Cu-SAPO-34催化剂在典型反应温度（即，200和350摄氏度）根据离子电导率的变化进行评估，并通过基于复阻抗的原位模量谱进行机械研究。发现沸石结构内的Cu离子的短程（局部）移动在很大程度上决定了这两种催化剂的NH3-SCR传感行为。NH3-溶剂化的、高度移动的Cu-I物质的形成显示出对两种催化剂的离子电导率的主要影响，因此，阻碍了在200 ℃下的NH3-SCR感测。通过模型Cu-SAPO-34系统的密度泛函理论计算表明，通过共吸附的NH3和NO将Cu-II还原为Cu-I显著削弱了Cu位点与CHA框架的配位，使得Cu-I物质具有高迁移率，这显著影响NH3-SCR传感。原位光谱和理论研究不仅揭示了Cu-CHA催化剂作为直接监测NH3-SCR的传感元件的机理，而且还使我们能够深入了解在不同反应条件下，不同温度和气体组成下NH3-SCR中活性Cu位点的形态。
The concept to utilize a catalyst directly as a sensor is fundamentally and technically attractive for a number of catalytic applications, in particular, for the catalytic abatement of automotive emission. Here, we explore the potential of microporous copper-exchanged chabazite (Cu-CHA, including Cu-SSZ-13 and Cu-SAPO-34) zeolite catalysts, which are used commercially in the selective catalytic reduction of automotive nitrogen oxide emission by NH3 (NH3-SCR), as impedance sensor elements to monitor directly the NH3-SCR process. The NH3-SCR sensing behavior of commercial Cu-SSZ-13 and Cu-SAPO-34 catalysts at typical reaction temperatures (i.e., 200 and 350 degrees C) was evaluated according to the change of ionic conductivity and was mechanistically investigated by complex impedance-based in situ modulus spectroscopy. Short-range (local) movement of Cu ions within the zeolite structure was found to determine largely the NH3-SCR sensing behavior of both catalysts. Formation of NH3-solvated, highly mobile Cu-I species showed a predominant influence on the ionic conductivity of both catalysts and, consequently, hindered NH3-SCR sensing at 200 degrees C. Density functional theory calculations over a model Cu-SAPO-34 system revealed that Cu-II reduction to Cu-I by coadsorbed NH3 and NO weakened significantly the coordination of the Cu site to the CHA framework, enabling high mobility of Cu-I species that influences substantially the NH3-SCR sensing. The in situ spectroscopic and theoretical investigations not only unveil the mechanisms of Cu-CHA catalyst as sensor elements for direct NH3-SCR monitoring but also allow us to get insights into the speciation of active Cu sites in NH3-SCR under different reaction conditions with varied temperatures and gas compositions.