Selective elimination of cation in straight channel of ZSM-5 zeolite and relaxation movements of cation

Abstract

By ion-exchanging Na-ZSM-5 with benzyltrimethylammonium (BTMA⁺) ion, only Na⁺ ion in the straight channel, Na(S), was partially eliminated and movements of Na⁺ ions in both exchanged and unexchanged ZSM-5 were studied by a dielectric method. It was found that there were two types of Na⁺ ion in ZSM-5 and each Na⁺ ion caused one relaxation loss. The loss in the higher frequency side for exchanged ZSM-5 became smaller in comparison with that for unexchanged ZSM-5. From this result, it was concluded that the loss in the higher frequency side was attributable to the movement of Na(S) and the loss in the lower frequency side was due to the movement of Na(Z) (Na⁺ ion in the zigzag channel). From theoretical considerations on the relaxation movements, each activation energy measured was assigned to the energy required for each Na⁺ ion to jump from the quasi stable site to the stable site. The water molecule preferentially adsorbed to Na(S) and avoided Na(Z). The difference in affinity to water molecules between Na(S) and Na(Z) was explained as the heat of adsorption to Na(S) being larger than that to Na(Z).