Synthesis, Characterization And Catalytic Applications Of Nanosheets Structure Of ZSM-5

Zeolites are widely used as a class of classic catalyst with advantages of large surface area, high hydrothermal stability and uniform rich pore. However, applications of the traditional zeolite are limited due to its small pore size. It means large molecules get into the pore very difficult, and the large molecules that formed in the tunnel can’t escape quickly, which often leads to side reactions. In recent years, preparation of hierarchical zeolites with nanosheets structure is becoming a hot topic. Double heads quaternary ammonium surfactant agents not only can guide micropore-forming, but also can limit growth of zeolite crystals. It is the key to form nanosheets-structure. However, double heads quaternary ammonium surfactant agents are quite expensive and synthesis process are complicated, which limitited the industrial applications of zeolites nanosheets.. Therefore, developing a new method to synthesize MFI-type zeolites with nanosheets structure by using cheap and easily obtained quaternary ammonium agents is the key issue to be solved.In this work, organic quaternary ammonium was used as a microporous templating agent, and long-chain cationic surfactants were used as a structure-directing agent (SDA). The optimal synthesis conditions for preparation of ZSM-5 nanosheets were evaluated by controlling the molar ratio of synthetic solution as 40SiO2:xA12O3:15TPA:25KOH:3000H2O:ySDA, ZSM-5 zeolite nanosheets with an average thickness of about 10nm was obtained after hydrothermal crystallization at 175℃ for a certain time. ZSM-5 nanosheets were analyzed and characterized by using SEM、XRD、NMR、FT-IR and TEM. The catalytic properties of prepared ZSM-5 nanosheets were tested by the methanol to olefins (MTO) and toluene alkylation with methanol (TAM) reactions.First, ZSM-5 nanosheets was synthesized by changing (1) Silicalite-1 seed; (2) the crystallization time; (3) silica to alumina ratio; (4) species of organic quaternary ammonium salt; (5) pH value of synthetic fluids; (6) species and amounts of long-chain cationic surfactant. ZSM-5 with different morphologies was obtained. ZSM-5 nanosheets with an average thickness of lOnm and specific surface area of 236m2/g, were synthesized successfully.Secondly, catalytic performance of the ZSM-5 prepraed with different morphologies was studied in MTO reaction. ZSM-5 nanosheets held higher light olefins selectivity (selectivity of ethylene, propylene and olefins is 25%,31% and 66%, respectively). Meanwhile, TAM catalytic performance of ZSM-5 nanosheets also showed good catalytic activity in TAM reaction.Finally, nano-carbon partiles were added into the synthesis system of ZSM-5 nanosheets as hard templatie to create mesoporous. Even more, magnetic Fe3O4 nanoparticles were even evolved into the ZSM-5 nanosheets structure and making it easy to be separated in some special reactions.