Hydrothermal Synthesis Of Hierarchical ZSM-5/Beta Composite Zeolites Assisted By Aerosol Method

Zeolite ZSM-5 and Beta are important solid acid catalysts in the industrial catalysis field.ZSM-5 zeolite,which possesses a two-dimensional 10-membered ring channel system,has several advantages such as strong acidity,good thermal and hydrothermal stability,high mechanical strength and so on.However,it still exits problems of diffusion limitation and acid sites accessibility in the macromolecular catalytic reactions such as heavy oil cracking.Zeolite Beta with a three-dimensional 12-membered ring channels facilitates the diffusion of larger molecules owing to its larger pore size.This study aims to synthesize the composite zeolite with suitable pore structure and acidity by combining the advantages of their structures and properties.By adjusting the pore structure and the acidity,the catalytic performance of the composite zeolite will be enhanced by the synergistic effect.The above research may broaden the applications of the composite zeolites in the fields of petroleum chemical industry and fine chemicals.Based on the above ideas,the hierarchical ZSM-5/Beta composite zeolites were synthesized by an aerosol-assisted hydrothermal method in this study.The physicochemical properties of the ZSM-5/Beta composite zeolites were analyzed by various characterization methods,and the catalytic performance of the composite catalysts was evaluated by1,3,5-triisopropylbenzene（1,3,5-TIPB）cracking reaction.The main contents are as follows:Firstly,the Z-50%/B-50%sample was synthesized by an aerosol-assisted hydrothermal method.The synthesis conditions such as crystallization temperature,crystallization time and the amounts of template were investigated.The optimal synthesis conditions were obtained as follows:T=150℃,TEAOH/Si O₂=0.15,t=24 h.This method can decrease the crystallization time,the template amount and the discharge of sewage.Compared with pure ZSM-5 and Beta zeolites,the ZSM-5/Beta composite zeolites exhibit improved catalytic performance in the cracking reaction of 1,3,5-TIPB due to its larger mesoporous pore volume,external surface area as well as suitable acidity.Secondly,the aerosol-assisted hydrothermal method was extended to synthesize the ZSM-5/Beta composite zeolites with different mass ratios.The distinctions of their crystal phase structures,morphologies,pore structures and acidities were also studied by various characterization methods.The results indicate that this method can control the mass ratio of each component more accurately.By adjusting the pore structures and acidities,the composite zeolites exhibit good catalytic performances in the cracking reaction of 1,3,5-TIPB.