posted on 2024-01-17, 18:37authored byZhongqi Liu, Yu Fu, Yulong Shan, Tongliang Zhang, Yingjie Wang, Jinpeng Du, Yu Sun, Guangzhi He, Xiaoyan Shi, Yunbo Yu, Hong He
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 Cu2+ ions to CuOx during HTA in KFI. Specifically, the rate-determining
step is the hydrolysis of Cu2+ in KFI but the cross-cage
migration of Cu(OH)2 in CHA. Therefore, the inclusion of
two Cu2+ 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
Cu2+ 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 Cu2+ 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 Cu2+ ions.