Synthesis of Zeolite Monolith with Hierarchical Micro/Macropores by Ice-Templating and Steam-Assisted Crystallization

Zeolite monolith was synthesized by ice-templating and steam-assisted crystallization (SAC) by using a structure-directing agent (SDA). The precursor silica gel was prepared by applying ice-templating to the hydrogels synthesized from colloidal silica. Sodium aluminate (NaAlO2) was supported in the precursor by impregnation to prepare zeolite monolith. Silicalite monolith or zeolite monolith with three-dimensionally interconnected macropores was synthesized by SAC of the precursor by using tetrapropylammonium hydroxide as SDA. The monolith had the continuous macropores, and the surface of these macropores was densely covered with zeolite crystals. The crystals were identified as MFI-type by XRD and had a well ordered microporous structure. Since the macropores, which were formed by ice-templating, were directly connected to the micropores of the synthesized zeolite crystals, the synthesized zeolite monolith had the hierarchical structure of macropores and micropores. The macroporous structure of monolith could be controlled by the freezing conditions because the macropore size became large with the decrease in freezing rate of hydrogels. The BET surface area and the degree of crystallinity of zeolite monolith were increased up to 347 m(2)/g and 89 % by SAC. When the zeolite monolith was synthesized by changing the Si/Al ratio, the crystallization rate increased with the increase in Si/Al ratio, and the hydrophilic or hydrophobic property was also controlled by choosing the Si/Al ratio.