Preparation of hollow ZSM-5 crystals in the presence of polyacrylamide

Hollow ZSM-5 crystals were successfully synthesized through a simple one-step hydrothermal crystallization method in the presence of polyacrylamide (PAM) as template. The influences of crystallization temperature, PAM concentration, and the type of PAM on the morphology and pore structure of hollow ZSM-5 zeolite as well as the stability and formation mechanism of hollow structure were investigated. Hollow ZSM-5 crystals could be synthesized by adding three types of PAM with different surface groups. Crystallization temperature and PAM concentration played crucial roles in the formation of hollow ZSM-5 crystals. Low crystallization temperature or high PAM concentration was beneficial for the formation of hollow ZSM-5 crystals with embedded large voids in the framework structure. Egg-shell like hollow ZSM-5 crystals formed with less amount of PAM at high temperature due to the decomposition of the PAM network. Moreover, the surface walls of those hollow ZSM-5 crystals possessed microporous crystalline framework. Hollow ZSM-5 crystals exhibited good thermal and hydrothermal stability, and anti-pressure ability. ZSM-5 crystallization in the presence of PAM was in good agreement with the surface-to-core crystallization process. The fast growth of ZSM-5 nuclei on the surfaces of PAM hydrogel resulted in the formation of single crystals with hollow structure after they consumed the synthesis gel and ZSM-5 nuclei in the PAM hydrogel network.

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► Hollow ZSM-5 crystals could be synthesized by using polyacrylamide as template.
► Hollow ZSM-5 with voids formed under low temperature or high PAM concentration.
► Egg-shell like hollow ZSM-5 formed with less amount of PAM at high temperature.
► The walls of hollow ZSM-5 crystals possessed microporous crystalline framework.