Ion-exchange studies in the synthetic zeolite ZK-5

Biogas upgrading through kinetic separation of carbon dioxide and methane over Rb- and Cs-ZK-5 zeolites

“…1) and thus making it unavailable for exchange anymore. 32 Similar phenomena have been reported for zeolites A, X, Y upon exchanges with Rb + or Cs + ions starting from the sodium form of the zeolite. 32 On the contrary, this would probably not be the case for K + cations (in case of K-ZK-5 as a starting material) given their larger size making it energetically highly unfavorable to reside in a M2 site.…”

“…32 Similar phenomena have been reported for zeolites A, X, Y upon exchanges with Rb + or Cs + ions starting from the sodium form of the zeolite. 32 On the contrary, this would probably not be the case for K + cations (in case of K-ZK-5 as a starting material) given their larger size making it energetically highly unfavorable to reside in a M2 site. We realize that the above statements are all tentative explanations and a further study would be required to completely clarify the underlying principles governing the exchange with large cations such as K + , Rb + and Cs + within KFI.…”

“…These results seem at rst sight contradictory with the observed cut-offs during exchange with Rb or Cs salts in previous studies (vide infra). 29,32 However, Dyer and Enamy used the original synthesis method from Kerr 30 in which a large structure directing agent (1,4-dimethyl-1,4-diazonobicyclo[2.2.2]octanedihydroxide) is employed. As a result, quaternary ammonium ions are present in the ZK-5 pores aer synthesis.…”

“…29 The apparent cut-offs at 50-60% exchange upon ion-exchange of ZK-5 with a Rb or Cs salt solution have been related to the restricted access for Rb + /Cs + cations to the puckered 8 MRs once the preferred at 8 MRs are lled with Rb + /Cs + cations. 29,32 Therefore, rst instance, it does not seem possible to prepare a ZK-5 structure that is fully exchanged with Rb or Cs. 29,[32][33][34] The main goal and novelty of this study is to investigate whether ZK-5 structures in which most of the interconnecting central window sites are lled with large cations hold (large) potential for industrial CO 2 /CH 4 separations such as biogas separations or not.…”

“…29,32 Therefore, rst instance, it does not seem possible to prepare a ZK-5 structure that is fully exchanged with Rb or Cs. 29,[32][33][34] The main goal and novelty of this study is to investigate whether ZK-5 structures in which most of the interconnecting central window sites are lled with large cations hold (large) potential for industrial CO 2 /CH 4 separations such as biogas separations or not. As such, we want to contribute to the further showing the two types of cages, which are linked via double six ring units.…”