Impact of mild hydrothermal aging on kinetics of NH 3, NO, SO 2 and CO oxidation reactions on Cu/SSZ-13 catalyst

Cu/SSZ-13 is a catalyst commonly used for selective catalytic reduction (SCR) of nitrogen oxides (NO x ) in diesel engine exhaust. Standard configurations are based on SCR preceded by an oxidation catalyst, however, a close -coupled SCR configuration appears relevant for upcoming regulations addressing cold -start emissions. Two often discussed ion -exchanged Cu sites in Cu/SSZ-13 are denoted ZCuOH and Z 2 Cu, where Z represents an Al atom in the zeolite framework. Mild hydrothermal aging (HTA) causes Cu redistribution within the catalyst; ZCuOH sites transform into more stable Z 2 Cu species. In this work, the effect of mild HTA on NH 3 , NO, SO 2 , and CO oxidation is studied on a commercial Cu/SSZ-13 sample. Temperature -programmed reaction experiments, performed in a lab reactor, and previously published catalyst characterization data using H 2 -TPR, NH 3 -TPD, and DRIFTS were used to build and validate a mathematical model. It couples the kinetics of the oxidation reactions with ZCuOH and Z 2 Cu concentration evolution during mild HTA. The model uses two distinct rate coefficients for ZCuOH and Z 2 Cu sites, allowing prediction of the catalyst activity during aging. The results suggest that the rate coefficients for the studied reactions on Z 2 Cu are effectively nil, so the observed activity in NH 3 , NO, SO 2 , and CO oxidation can be attributed solely to ZCuOH sites.