Synthesis And Characterization Of ZSM-5 Zeolite

ZSM-5 zeolite has excellent hydrothermal stability,shape selectivity,solid aciditybecause of its unique ten-membered ring pore structure.However,the formation of carbon deposits in the catalytic reaction of macromolecules leads to the deactivation of the catalyst due to its smaller pores?<1 nm?.Therefore,it is extremely important to avoid inactivation and carbon deposits of ZSM-5 by reducing the size of ZSM-5 to shorten the diffusion path of the material and increasing the pore size of ZSM-5 by synthesizing the hierarchical structure.In this paper,we mainly study the synthesis of small-size ZSM-5 and ZSM-5 aggregates with hierarchical structure.?1?TPAOH as template,industrial silica sol as silicon source,and aluminum sulfate as aluminum source to synthesize small size ZSM-5.ZSM-5 with small size,high crystallinity and good uniformity is synthesized by adjusting the ratio of silica to alumina,alkali amount,crystallization method,seed addition amount,and water amount of the synthesis system.The results show that increasing the silica-alumina ratio and alkali amount,two-step temperature change crystallization of the synthetic liquid are favorable to the formation of ZSM-5 with good uniformity and small size;The seeds with a size of 80 nm are added,the ZSM-5particles are significantly reduced from 0.7¹.6?m to 0.5⁰.7?m with the amount of seeds from 0.1% to 1.0%.In the system of H₂O/SiO₂=20,the uniformity of zeolite particles is poor,H₂O/SiO₂ is increased to 30 and 40,small size ZSM-5 with uniform crystallite sizes of 0.6 ?m and 0.45 ?m are obtained,respectively.?2?Hydrothermal Synthesis of ZSM-5 aggregates using organic template and studying its crystal transformation behavior.The results show that the zeolite transforms from monodisperse circular particles with MFI structure into rod-like stacked,nanorod-like stacked elliptic zeolite aggregates with MOR-doped when the SiO₂/Al₂O₃ is reduced from 400 to 30,20.The zeolite with SiO₂/Al₂O₃=20 changes from partially colloidal to nanorod-like stack,flake-like stack with the increase of alkalinity.With the increase of the amount of TPAOH,the particle size of SiO₂/Al₂O₃=400 is gradually reduced and with MFI structure,the zeolite of SiO₂/Al₂O₃=20 have gradually changs from the previous nanorod-like stack into flake-like stack,and the flakes are peeled off and converted into a mixture of MOR and ANA zeolites.?3?Hydrothermal synthesis of hierarchical nano-ZSM-5 aggregates are studied in the template-free system.The influence of seed size,seed addition amount,alkali amount,crystallization time,and additives on the aggregates are investigated.It is concluded that80 nm seeds are more likely to induce aggregates than 200 nm seeds.The 0.45-2.5?m nano-ZSM-5 aggregates are obtained which consists of 20-110 nm nano-primary particles when the seed addition between 0.1% and 10%.The size of aggregates decreases while the primary particle size decreases first and then increases with increasing alkalinity.ZSM-5aggregates are formed completely after crystallization for 12 h.Adding electrolyte salts such as Na Cl,Na₂CO₃,and NH₄F,the nano-primary particles on the aggregates are more dispersed and are not conducive to agglomeration.Adding the mesoporous template CTAB to the system is not conducive to the crystallization of ZSM-5.