Institute of Inorganic Chemistry, RWTH Aachen University, Landoltweg 1a, 52074, Aachen, Germany.
Guangdong Provincial Key Laboratory of Atmospheric Environment and Pollution Control, School of Environment and Energy, South China University of Technology, 510006, Guangzhou, China; National Engineering Laboratory for VOCs Pollution Control Technology and Equipment, 510006, Guangzhou, China.
Chemosphere. 2020 Jul;250:126272. doi: 10.1016/j.chemosphere.2020.126272. Epub 2020 Feb 20.
Reduction of harmful nitrogen oxides (NO) from diesel engine exhausts is one of the key challenges in environmental protection, and can be achieved by NH-assisted selective catalytic reduction (NH-SCR) using copper-exchanged chabazite zeolites (i.e. Cu-CHA, including Cu-SSZ-13 and Cu-SAPO-34) as catalysts. Understanding the redox chemistry of Cu-CHA in NH-SCR catalysis is crucial for further improving the NO reduction efficiency. Here, a series of Cu-SSZ-13 catalysts with different Cu ion exchange levels were prepared, thoroughly characterized by different techniques such as X-ray diffraction, diffuse reflectance ultraviolet-visible spectroscopy and temperature-programmed desorption using NH as a probe molecule, etc., and tested in NH-SCR reactions under steady-state conditions. In situ studies by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), supplemented with density-functional theory calculations, provided solid evidence for the formation of ammonium ion (NH) intermediates resulting from the reduction of Cu to Cu by co-adsorbed NH and NO molecules on Cu-SSZ-13. Catalytic relevance of the NH intermediates, as demonstrated by an increase of NO conversion over Cu-SSZ-13 pre-treated in NH/NO atmosphere, can be attributed to the formation of closely coupled Cu/NH pairs promoting the Cu re-oxidation and, consequently, the overall NH-SCR process. This study thus paves a new route for improving the NH-SCR efficiency over Cu-CHA zeolite catalyst.
从柴油机废气中减少有害的氮氧化物（NO）是环境保护的关键挑战之一，可以通过使用铜交换的丝光沸石（即 Cu-CHA，包括 Cu-SSZ-13 和 Cu-SAPO-34）作为催化剂的 NH 辅助选择性催化还原（NH-SCR）来实现。了解 NH-SCR 催化中 Cu-CHA 的氧化还原化学对于进一步提高 NO 还原效率至关重要。在此，制备了一系列具有不同 Cu 离子交换水平的 Cu-SSZ-13 催化剂，通过 X 射线衍射、漫反射紫外可见光谱和程序升温脱附等不同技术进行了彻底的表征，并用 NH 作为探针分子在稳态条件下进行了 NH-SCR 反应测试。漫反射红外傅里叶变换光谱（DRIFTS）的原位研究，辅以密度泛函理论计算，为 Cu-SSZ-13 上 co-adsorbed NH 和 NO 分子还原 Cu 至 Cu 形成铵离子（NH）中间体提供了确凿的证据。NH 中间体的催化相关性，如在 NH/NO 气氛中预处理的 Cu-SSZ-13 上 NO 转化率的增加所示，可以归因于形成紧密耦合的 Cu/NH 对，促进了 Cu 的再氧化，从而促进了整个 NH-SCR 过程。因此，这项研究为提高 Cu-CHA 沸石催化剂的 NH-SCR 效率开辟了一条新途径。
