Hierarchical mesoporous zeolites with controllable mesoporosity templated from cationic polymers

Hierarchical mesoporous Beta (Beta-H) and ZSM-5 (ZSM-5-H) zeolites with various mesoporosities were synthesized in the presence of small organic cations of tetraethylammonium and tetrapropylammonium, and mesoscale cationic polymers of polydiallyldimethylammonium chloride and dimethyldiallyl ammonium chloride acrylamide copolymer, respectively. Nitrogen isotherms of Beta-H and ZSM-5-H both exhibited broad hysteresis loops at relative pressure of 0.7–0.95, indicating the presence of hierarchical mesopores in these samples. Barrett–Joyner–Halenda analysis showed that the mesopores in Beta-H and ZSM-5-H are in the range of 5–40 nm. Transmission electron microscopy images confirmed the co-presence of ordered micropores and hierarchical mesopores. Interestingly, nitrogen adsorption and thermogravimetric analysis showed that the mesoporosity in Beta-H and ZSM-5-H could be adjusted by the mesoscale cationic polymers added in the starting gels. The stability tests showed both Beta-H and ZSM-5-H samples have higher hydrothermal stability than the conventional mesoporous materials. These features of Beta-H and ZSM-5-H, including hierarchical porosity, adjustable mesopore volume, large surface area and hydrothermal stability, would be very important for zeolites as catalysts with fast mass transport, accessible porosity, high activities and stabilities for the catalytic conversion of bulky molecules.