Understanding the Hydrothermal Stability of Potential NH<sub>3</sub>-SCR Catalyst Cu-KFI Zeolite
Zhongqi Liu, Yu Fu, Yulong Shan, Tongliang Zhang, Yingjie Wang, Jinpeng Du, Yu Sun, Guangzhi He, Xiaoyan Shi, Yunbo Yu, Hong He
Abstract
Al-rich Cu-KFI was found to withstand hydrothermal aging (HTA) at 800 °C, while Cu-CHA with a similar Si/Al ratio was deactivated since a much higher energy barrier was required to transform Cu 2+ ions to CuOx during HTA in KFI. Specifically, the rate-determining step is the hydrolysis of Cu 2+ in KFI but the cross-cage migration of Cu(OH) 2 in CHA. Therefore, the inclusion of two Cu 2+ ions in one repeat unit of KFI does not significantly promote CuOx production. However, the accumulated CuOx cannot be completely avoided under such severe hydrothermal aging. It may originate from Cu 2+ in the same cage or adjacent cages. This shorter diffusion effectively mitigated the structural integrity deterioration of KFI in comparison to CHA. Nevertheless, HTA reduced the number as well as the reactivity of residual Cu 2+ ions in Cu-KFI zeolite catalysts. Quantitative results determined that the activity and stability of the catalyst were maximized when the average lta cage contained about 1.4 Cu 2+ ions.