A Complete Multisite Reaction Mechanism for Low-Temperature NH3-SCR over Cu-CHA
A Complete Multisite Reaction Mechanism for Low-Temperature NH3-SCR over Cu-CHA
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DOI：
10.1021/acscatal.0c00440
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发表时间：
2020-05-15
期刊：
影响因子：
12.9
通讯作者：
Gronbeck, Henrik
中科院分区：
文献类型：
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作者：
Chen, Lin;Janssens, Ton V. W.;Gronbeck, Henrik
由于活性中心的动态特性，很难揭示氨助选择性催化还原氮氧化物(SCR)的反应路径。在这里，我们用密度泛函理论计算提出了低温NH3-SCR的完整反应机理。该反应在氨溶铜阳离子、Cu(NH3)(2+)和Bronsted酸位上以多位方式进行。氧的活化和关键中间体HONO和H2NNO的形成发生在铜位上，而Bronsted酸位则促进HONO和HNNO分解为N-2和H2O。NO的活化和反应是通过形成亚硝酸根(NO+)或亚硝酸盐(NO2-)中间体进行的。这些低温机理考虑了铜中心的动态特性，其中氧活化需要成对的铜(NH3)(2+)络合物，而HO-NO和H3N-NO偶联可能发生在单个络合物上。NH_3溶剂化有助于铜对的形成和分离。完整的反应机理与测量的动力学数据相一致，为今后低温NH3-SCR反应的改进提供了坚实的基础。
The dynamic character of the active centers has made it difficult to unravel the reaction path for NH3-assisted selective catalytic reduction (SCR) of nitrogen oxides over Cu-CHA. Herein, we use density functional theory calculations to suggest a complete reaction mechanism for low-temperature NH3-SCR The reaction is found to proceed in a multisite fashion over ammonia-solvated Cu cations Cu(NH3)(2+) and Bronsted acid sites. The activation of oxygen and the formation of the key intermediates HONO and H2NNO occur on the Cu sites, whereas the Bronsted acid sites facilitate the decomposition of HONO and H2NNO to N-2 and H2O. The activation and reaction of NO is found to proceed via the formation of nitrosonium (NO+) or nitrite (NO2-) intermediates. These low-temperature mechanisms take the dynamic character of Cu sites into account where oxygen activation requires pairs of Cu(NH3)(2+) complexes, whereas HO-NO and H3N-NO coupling may occur on single complexes. The formation and separation of Cu pairs is assisted by NH3 solvation. The complete reaction mechanism is consistent with measured kinetic data and provides a solid basis for future improvements of the low-temperature NH3-SCR reaction.