Low-Temperature Standard-SCR over Cu-SSZ-13: Selective Inhibition of the Oxidation Half-Cycle by Mild Hydrothermal Aging

Abstract

The impact of mild hydrothermal aging (HTA) on low-temperature (150-200 °C) Standard-SCR is investigated using transient response methods and transient kinetic analysis. We decouple the Reduction and the Oxidation Half-Cycles (RHC and OHC) of the Standard-SCR redox mechanism to study them independently. While the RHC rates are essentially unaffected, OHC is inhibited by mild HTA. By equating the estimated rate expressions (both 2nd order in Cu sites, OHC with O2 as the sole oxidant), we predict exactly the steady-state low-temperature Standard-SCR performance in terms of both NO conversion and bed-average Cu redox state, as well as the detrimental effect of mild HTA on the DeNOx efficiency. We also demonstrate that the DeNOx activity of the aged catalyst can be precisely restored by incrementing the oxygen partial pressure in proportion to the drop of the OHC rate constant, as predicted by our simple two-reaction model. These findings offer valuable insights into the design of next-generation urea-SCR exhaust gas aftertreatment (EGA) systems featuring enhanced cold-start performance and durability under aging conditions.