Standard NH3-SCR and N2O formation kinetics over Cu-CHA monolith catalysts: transient and steady-state redox models

Transient Response Methods (TRMs) coupled with kinetic analysis are powerful tools to investigate the mechanism of catalytic reactions. In this work we apply them to study the redox chemistry of low temperature Standard-SCR and N2O formation over a model Cu-CHA catalyst. Two monolith samples with different washcoat loadings were tested using transient protocols varying temperature, space velocity, pressure and feed composition. Kinetic analysis of NO conversions and oxidized Cu fractions confirmed the dual-site mechanisms of the reduction (RHC) and oxidation (OHC) half-cycles, with quadratic dependences on the CuII and CuI species, respectively. N2O formation was also successfully predicted by incorporating an unselective CuII reduction (RHC_N2O) pathway in the redox model. Eventually, a global regression on the whole dataset provided calibrated rate parameters of the three reactions: RHC, OHC and RHC_N2O. The resulting redox model accurately describes the steady-state DeNOx activity and selectivity across the whole range of investigated conditions.