Effect of the hydrothermal aging temperature and Cu/Al ratio on the hydrothermal stability of CuSSZ-13 catalysts for NH3-SCR

Abstract

The effects of the hydrothermal aging temperature on the catalytic performance and stability of CuSSZ-13 catalysts with various Cu/Al ratios were studied. The conversions of NO and NH₃ were tested in the standard NH₃-SCR reactions. The NH₃-SCR activity of the catalysts decreased with the increasing hydrothermal aging temperature. Remarkably, the reduction was more significant as the Cu/Al ratio increased. The physicochemical properties of the samples were characterized by means of a number of analytical techniques. The results show that the hydrothermal stability of the CuSSZ-13 catalyst decreased with the increase in the hydrothermal aging temperature and Cu/Al ratio in the catalyst. Such a decrease was attributed to a drop in the number of isolated Cu²⁺ (in D6R and CHA cage). The transformation of the Cu²⁺ ions into new species (Cu²⁺ on Al₂O₃) depended on the collapse of the SSZ-13 structure after the hydrothermal aging treatment and was more likely to appear in the high Cu/Al-ratio samples and at a higher aging temperatures. The phase transformation of Cu²⁺ to agglomerated Cu_xO also occurred during the hydrothermal aging process. The formation of a large number of Cu_xO species might destroy the SSZ-13 structure, leading to deactivation of the catalyst.