The Effects of Created Mesopores in ZSM-5 Zeolites by an Alkali Treatment on Water Adsorption

抄録

Three kinds of ZSM-5 (MFI structure) zeolites [SiO₂/Al₂O₃=23.8 (Na form), 39.0 (NH₄ form) and 193(NH₄ form)] were alkali-treated, and the changes in structural and water adsorptive properties were investigated. With the alkali treatment, the MFI structure was preserved; a siliceous species was selectively dissolved from the framework of a zeolite, and mesopores were created in the zeolites. At the same time, NH₄-form ZSM-5 zeolites (SiO₂/Al₂O₃=39.0 and 193) were ion-exchanged to form Na in an aqueous solution of NaOH. In particular, for ZSM-5 (SiO₂/Al₂O₃=23.8), the water adsorption changed with the alkali treatment. The difference in the amount of adsorbed water on the zeolite between 30°C (adsorption temperature) and 100°C (desorption temperature) increased by the treatment. The desorption temperature of water adsorbed at the stronger site decreased from 106 to 72°C with the alkali treatment. These results indicate that the introduction of mesopores in ZSM-5 contributed to the enhanced water adsorption.