Journal
ANGEWANDTE CHEMIE-INTERNATIONAL EDITION
Volume 60, Issue 13, Pages 7197-7204Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/anie.202014926
Keywords
Cu-CHA; NH3-SCR; nitrogen oxides; reaction mechanisms; reduction half-cycle
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Funding
- National Natural Science Foundation of China [51836006, U1609212]
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This study investigates the redox mechanism of Low-Temperature SCR on Cu-CHA using various techniques, proposing a Cu-II pair mediated pathway for the reduction half-cycle, challenging previous mechanistic proposals based on isolated Cu-II ions. The results highlight the important role of dinuclear Cu complexes in both oxidation and reduction reactions of Low-Temperature SCR.
Cu-CHA is the state-of-the-art catalyst for the Selective Catalytic Reduction (SCR) of NOx in vehicle applications. Although extensively studied, diverse mechanistic proposals still stand in terms of the nature of active Cu-ions and reaction pathways in SCR working conditions. Herein we address the redox mechanism underlying Low-Temperature (LT) SCR on Cu-CHA by an integration of chemical-trapping techniques, transient-response methods, operando UV/Vis-NIR spectroscopy with modelling tools based on transient kinetic analysis and density functional theory calculations. We show that the rates of the Reduction Half-Cycle (RHC) of LT-SCR display a quadratic dependence on Cu-II, thus questioning mechanisms based on isolated Cu-II-ions. We propose, instead, a Cu-II-pair mediated LT-RHC pathway, in which NO oxidative activation to mobile nitrite-precursor intermediates accounts for Cu-II reduction. These results highlight the role of dinuclear Cu complexes not only in the oxidation part of LT-SCR, but also in the RHC reaction cascade.
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