Mauro Bracconi

Operando UV-Vis spectroscopy combined with transient kinetic analysis is used to directly quantify the kinetics of the oxidation half-cycle (OHC) in low-temperature NH₃-SCR over Cu-CHA. Operando UV-Vis measurements further provide direct evidence that H₂O promotes the OHC via a NO-independent mechanism and induces the formation of an additional stable Cu(II) species under O₂/H₂O conditions, indicating that H₂O participates in the kinetically relevant step of Cu(I) reoxidation. Dispersion-corrected DFT calculations reveal the molecular origin of this promotion: free-energy analysis predicts a H₂O-assisted dissociation of the [Cu2(NH3)4O2]2+ peroxo intermediate, enabling redistribution of oxidative equivalents required to complete Cu(I) oxidation via a H₂O₂-mediated pathway. This mechanism provides a molecular-level explanation for the experimentally observed promoting effect of H₂O on the OHC. The calculated activation parameters are in excellent agreement with experiment, establishing quantitative consistency between the proposed molecular mechanism and macroscopic kinetics. Together, these results resolve the Cu redox chemistry of low-temperature NH₃-SCR by elucidating the transformation from the peroxo Cu(II) intermediate to the linear diamine Cu(I) species while satisfying the experimentally observed stoichiometry, which involves one NO converted per Cu equivalent in each redox cycle. Overall, this work provides a kinetically-consistent closure of the NH₃-SCR catalytic cycle by integrating the oxidation and reduction half-cycles into a unified redox mechanism that identifies H₂O as a key mediator of Cu redox dynamics.

We employ UV/Vis Diffuse Reflectance spectroscopy directly coupled with a packed bed flow reactor to extract quantitative kinetic information. We use as a show‐case the Cu^II/Cu^I redox dynamics during the reduction half cycle of the NH₃‐Selective Catalytic Reduction (SCR) on Cu‐CHA catalysts. Our measurements enable quantification of the fraction of oxidized Cu, reconstructed by Multivariate Curve Resolution (MCR) together with monitoring of the gas‐phase evolution during the reaction. These data both on the dynamics of the gas‐phase and of the active site oxidation state have been used to assess the reduction half cycle rate equation and estimate the rate constant. Our results in terms of reaction orders and kinetic constant are in line with previous findings in the literature. Overall, our results demonstrate that the combined analysis of the UV spectra and of the gas‐phase dynamics provides converging and unparalleled kinetic insight: this approach effectively resolves ambiguities concerning RHC kinetics and mechanism. More in general, this work provides evidence that operando spectroscopy can be used to extract quantitative kinetic information on catalytic cycles.

We employ UV/Vis Diffuse Reflectance spectroscopy directly coupled with a packed bed flow reactor to extract quantitative kinetic information. We use as a show‐case the Cu^II/Cu^I redox dynamics during the reduction half cycle of the NH₃‐Selective Catalytic Reduction (SCR) on Cu‐CHA catalysts. Our measurements enable quantification of the fraction of oxidized Cu, reconstructed by Multivariate Curve Resolution (MCR) together with monitoring of the gas‐phase evolution during the reaction. These data both on the dynamics of the gas‐phase and of the active site oxidation state have been used to assess the reduction half cycle rate equation and estimate the rate constant. Our results in terms of reaction orders and kinetic constant are in line with previous findings in the literature. Overall, our results demonstrate that the combined analysis of the UV spectra and of the gas‐phase dynamics provides converging and unparalleled kinetic insight: this approach effectively resolves ambiguities concerning RHC kinetics and mechanism. More in general, this work provides evidence that operando spectroscopy can be used to extract quantitative kinetic information on catalytic cycles.

DFT and CI-NEB are used to investigate potential energy surfaces and determine rate constants of C ₂ H ₂ deposition on graphene edges. Chemical lumping enables implementation of the proposed rate constants in pyrocarbon deposition kinetic models.