Hydrothermal stability of CuSSZ13 for reducing NOx by NH₃

The hydrothermal stability of CuSSZ13 catalysts with respect to their Cu/Al ratio has been investigated to understand the deactivation mechanism of their catalytic activity for NO reduction by NH₃/SCR. The decline of the deNOx activity due to the hydrothermal aging became more severe as the Cu/Al ratio increased. Results of ESR, H₂-TPR and DRIFT studies indicated that the D6R sites are occupied first by Cu²⁺ ions (α species) up to their accommodation capacity, followed by the occupation of the CHA sites (β species) with the increase in the Cu/Al ratio. The β species agglomerate more readily than α species due to their less stable nature, leading to the formation of CuOx. The CuOx may grow to destroy the zeolite cage and channel, resulting in the collapse of the SSZ13 structure, which is believed to be the primary cause for the hydrothermal deactivation of the CuSSZ13 catalyst.