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Abstract
Adsorption potentials in pores of ion-exchanged ZSM-5 zeolites MeZSM-5(Me = Li1+, Na1+, K1+, Rb1+, and Cs1+) are investigated theoretically using methane as a probe adsorbate. The potential U is considered to consist of a potential U pore for the cylindrical pore and a potential U cation for the cation site, located at an appropriate position in the pore. Calculated results for CH4-LiZSM-5 and for CH4-CsZSM-5 are presented as potential maps at different positions along the pore axis. These maps show complexities of the adsorption potentials around the cation site, particularly when the cation is large. The potential energy map for the CH4-NaZSM-5 system is similar to that of the CH4-LiZSM-5 system while the potential map of the CH4-RbZSM-5 system is similar to that of the CsZSM-5 system. The potential map of the CH4-KZSM-5 system also exhibits a character similar to that around a large cation, although not so marked. Good agreement between the experimental heat of adsorption and the heat of adsorption calculated with the potential energy is obtained for every CH4-MeZSM-5 system.