Synthesis Of Hierarchically ZSM-5and Its Catalytic Application

Hierarchical zeolites which combine micropore and mesopore have drawn much attention in the field of porous materials because of their potential catalytic applications in the industrial fields. These materials which combine the advantages of zeolites (strong acidity, hydrothermal stability and shape selectivity) and ordered mesoporous materials (large mesopore structure) have been proven to be the promising catalysts. Its synthesis, characterization and catalytic performance have gathered much attention. Templating method is a very important and effective way to fabricate hierarchical zeolites. However, the expensive templates and complicated synthesis processes limit its industrial application. So, in this thesis, we concentrated on developing cost effective, simple and feasible hierarchical zeolite synthesis methods and investigating their catalytic performance in synthesis of2,6-dimethylnaphthalene (2,6-DMN) by alkylation of2-methylnaphthalene (2-MN) with methanol.Hierarchical nanocrystalline stacked structural ZSM-5was hydrothermally synthesized by one-step using cheap vinyltriethoxysilane (VTES) as additive. The zeolite crystals’size and their pore structure can be tuned by the different amount of VTES. The catalytic performance of catalysts was investigated for methylation of2-MN with methanol to produce2,6-DMN. The results show that hierarchical ZSM-5(M-ZSM-5(0.1)) has higher activity and stability than micropore sample. The2-MN conversion was kept at around20%even when the reaction time is lOh. Moreover, the yield of2,6-DMN is about7%.It is very difficult to synthesis hierarchical zeolites by using traditional cationic surfactants as template. To over this problem, in the mater thesis, we synthesize hierarchical zeolite aggregates by using hexadecyl trimethyl ammonium bromide (CTAB) as template to assemble the zeolite seeds fabricated under reflux at80°C for24h without any cosolvent or additive. The zeolite aggregates’and the nanocrystals’size can be controlled by the amount of CTAB. So does their texture structure. However, too much CTAB would hinder zeolites growth and crystallization. Moreover, NaOH do good to zeolites growth and crystallization. In2,6-DMN synthesis, these samples showed better activity and stability than commercial micropore sample. However,2,6-DMN selectivity is poor. The sample which labeled as MZ(0.05) exhibited the best stability. The2-MN conversion was kept at around16.2%even when the reaction time is32h. Moreover, the yield of2,6-DMN keep more than6.8%f or over14h and the highest yield of2,6-DMN is7.8%.. Hierarchical ZSM-5zeolites with wormlike mesopore were synthesized by using TPOAC or the mixture of TPOAC and OTAC as template after3.5h microwave irradiation. Hierarchical ZSM-5zeolites were consisted of many lOnm nanozeolites. Their texture structure can be adjusted by different amount of TPOAC. However, too much TPOAC hinder zeolites growth and crystallization. In2,6-DMN synthesis, these samples showed better activity and stability than commercial micropore sample. However,2,6-DMN selectivity and the ratio of2,6-/2,7-DMN are poor. The sample which labeled as WMZ(0.03) displayed the best stability. The2-MN conversion was kept at around25%even when the reaction time is30h. The highest yield of2,6-DMN is7.6%.