Preparation Of Zn(Ga) Modified Nano ZSM-5 Molecular Sieve And Its Aromatization Reaction

In this thesis, nanosized ZSM-5 zeolites and Zn(Ga) modified ZSM-5 zeolites were synthesized by seed-induced method. Hierarchical ZSM-5 zeolites were prepared by citric acid and steam dealumination, respectively. The aromatization of 1-hexene was investigated in a flowing type fixed bed microreactor. To study the effect of seed heating time of conventional electric (CE) heating and microwave radiation (MW) heating, citric acid concentration, steaming time on the catalytic behavior of 1-hexene aromatization, various techniques, including XRD, SEM,27A1 MAS NMR,29Si MAS NMR,71Ga MAS NMR, N2 physical adsorption and desorption, NH3-TPD and Py-IR, were used in the characterization of the catalysts.The results show that the appropriate seed heating time of CE and MW method were 1 h and 25 min, respectively. Compared with CE heating method, ZSM-5 catalysts prepared by MW heating method exhibited higher BTX yield and lower deactivation rate in the 1-hexene aromatization due to the samller particle size, lower Bransted acid sites density and B/L ratio.After Zn(Ga) modification, the particle size decreased, mesoporous volume increased, B/L ratio decreased.71Ga MAS NMR results reveal that Ga atom was incorporated into ZSM-5 zeolites. Compared with nanosized ZSM-5 zeolites, Zn/AlHNZ5(20)-MW and GaHNZ5(20)-MW catalysts exhibited higher BTX yield of 58.38 wt.% and 59.42 wt.%, respectively.Citric acid dealumination and steam dealumination of Zn/AlHNZ5(20)-MW zeolite can effectively remove the framework Al species which resulted in the increase of mesoporous volume and decrease of Br(?)nsted acid sites as well as B/L ratio. The BTX yield and reaction stability in the 1-hexene aromatization of dealuminated Zn modified zeolites improved and Zn/AlHNZ5-st/16 catalyst exhibited the highest BTX yield of 66.42 wt.%.