通过原位紫外-可见光谱和瞬态 DFT 计算揭示 Cu-SSZ-13 沸石催化 NOx 还原中笼限制铜对的形成和反应性,Environmental Science & Technology

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通过原位紫外-可见光谱和瞬态 DFT 计算揭示 Cu-SSZ-13 沸石催化 NOx 还原中笼限制铜对的形成和反应性
Environmental Science & Technology ( IF 10.8 ) Pub Date : 2023-08-09 , DOI: 10.1021/acs.est.3c00458
Huarong Lei _{1,

2} , Dongdong Chen ₁ , Jia-Yue Yang ₃ , Abhishek Khetan ₄ , Jiuxing Jiang ₅ , Baoxiang Peng ₆ , Ulrich Simon _{2,

4} , Daiqi Ye ₁ , Peirong Chen ₁

Affiliation

菱沸石型小孔 Cu-SSZ-13 沸石的低温机理，这是一种用于重型车辆有毒 NO x 污染物的氨辅助选择性还原 (NH 3 -SCR)的_最_先进催化剂，仍然是一个争论，需要澄清以进一步提高 NH ₃ -SCR 性能。在这项研究中，我们建立了实验方案，通过原位紫外-可见光谱和低温NH ₃ -SCR催化过程中Cu -SSZ-13中Cu位点的动态氧化还原循环（即Cu ^II ↔ Cu ^{I ）}原位红外光谱。进一步将原位光谱观察与时间相关的密度泛函理论计算相结合，使我们能够识别两种笼内限制的瞬态，即 O ₂桥联铜二聚体（即μ-η 2 :η ^{2 -过氧化}^二氨基二铜）和接近配对的、化学非键合的 Cu ^I (NH ₃ ) ₂位点，并确认 Cu ^I (NH ₃ ) ₂对作为 O ₂桥联 Cu 二聚体的前体。比较瞬态实验揭示了Cu ^I (NH ₃ ) ₂对在低温下将NO还原为N _{2的特别高的反应性。}^{我们的研究证明了沸石限制下近似配对的 Cu I}位点的瞬时形成和高反应性的直接实验证据，并为在低温 NH 3 _-SCR催化中完成 Cu 氧化还原循环的单体到二聚 Cu 转化提供了新的见解超过 Cu-SSZ-13。

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Revealing the Formation and Reactivity of Cage-Confined Cu Pairs in Catalytic NOx Reduction over Cu-SSZ-13 Zeolites by In Situ UV–Vis Spectroscopy and Time-Dependent DFT Calculation

The low-temperature mechanism of chabazite-type small-pore Cu-SSZ-13 zeolite, a state-of-the-art catalyst for ammonia-assisted selective reduction (NH₃-SCR) of toxic NO_x pollutants from heavy-duty vehicles, remains a debate and needs to be clarified for further improvement of NH₃-SCR performance. In this study, we established experimental protocols to follow the dynamic redox cycling (i.e., Cu^II ↔ Cu^I) of Cu sites in Cu-SSZ-13 during low-temperature NH₃-SCR catalysis by in situ ultraviolet–visible spectroscopy and in situ infrared spectroscopy. Further integrating the in situ spectroscopic observations with time-dependent density functional theory calculations allows us to identify two cage-confined transient states, namely, the O₂-bridged Cu dimers (i.e., μ-η²:η²-peroxodiamino dicopper) and the proximately paired, chemically nonbonded Cu^I(NH₃)₂ sites, and to confirm the Cu^I(NH₃)₂ pair as a precursor to the O₂-bridged Cu dimer. Comparative transient experiments reveal a particularly high reactivity of the Cu^I(NH₃)₂ pairs for NO-to-N₂ reduction at low temperatures. Our study demonstrates direct experimental evidence for the transient formation and high reactivity of proximately paired Cu^I sites under zeolite confinement and provides new insights into the monomeric-to-dimeric Cu transformation for completing the Cu redox cycle in low-temperature NH₃-SCR catalysis over Cu-SSZ-13.

更新日期：2023-08-09

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