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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 CuII, thus questioning mechanisms based on isolated CuII‐ions. We propose, instead, a CuII‐pair mediated LT‐RHC pathway, in which NO oxidative activation to mobile nitrite‐precursor intermediates accounts for CuII 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. [ABSTRACT FROM AUTHOR]

• A kinetic model describing the reaction rate and Cu oxidation state was developed. • The dynamic transitions of CuCl 2 and CuCl were taken into account. • The steady-state kinetic model was obtained by the combined reduction and oxidation steps. • The method can be exploited to Mars–van Krevelen type redox reactions. A kinetic model was developed by taking into account the dynamic nature of the active sites in Mars–van Krevelen type catalytic reactions to predict the evolution of the reactant and product composition in the gas phase and the CuCl 2 concentration in the solid catalyst. The kinetic model at the steady-state of ethylene oxychlorination was obtained by combining transient experiments of the two half-reactions in the redox cycle, namely CuCl 2 reduced to CuCl by ethylene and CuCl oxidation by oxygen on the K-promoted CuCl 2 /γ-Al 2 O 3 catalyst. The dynamic transitions between CuCl 2 and CuCl of the active sites during the reactions are also modeled, and the contributions of two active sites, namely Cu coordination numbers of 4 and 3 in CuCl 2 were distinguished and included in the kinetic model. The kinetic models describe well the transient response of the reduction and oxidation steps as well as the reaction at the steady-state at different reaction conditions. Moreover, by combining the reactor modeling through a steady-state approach, the spatial-time resolved CuCl 2 profile and the C 2 H 4 reaction rate can be well predicted in comparison with the experimental results. The approach of both transient and steady-state kinetic modeling and simulation is supposed to have general relevance for a better understanding of Mars–van Krevelen type reactions. [ABSTRACT FROM AUTHOR]