Synthesis Of Hierarchical ZSM-5 Zeolite And Its Catalytic Performance

In addition to retaining the unique advantages of the traditional microporous ZSM-5 zeolite,the diffusion efficiency and the accessibility of the active sites of the hierarchical ZSM-5 zeolite are also improved,thereby reducing the activation energy of the reaction and increasing the efficiency of the catalytic reaction.However,the preparation of the hierarchical ZSM-5 zeolite also has the problems,such as high cost of the synthesis,low yield,and difficulty in industrialization.In this thesis,a set of hierarchical ZSM-5 zeolites were synthesized from the perspectives of cost reduction,solid yield improvement,and performance adjustment,and eventually,the hierarchical ZSM-5 zeolite catalysts were evaluated by the methanol and methane conversion reactions.First of all,in this thesis,a series of ZSM-5 zeolite nanosheets with different morphologies were synthesized in a synergistic effect by using the diquaternary ammonium salt surfactant C_16-6-6 as a structure-directing agent,and the content of the second template(single quaternary ammonium salt surfactant C_16-3)is adjusted in the synthesis.The results show that the ZSM-5 zeolite nanosheets could be effectively synthesized by C_16-6-6,however,as the amount of C_16-6-6 decreases in the synthesis,the thickness of the layered ZSM-5 zeolite inevitably increases.It was found that C_16-3played a cooperative crystallization role in the synthesis,which could effectively control the thickness and pore structure of the resulting layered ZSM-5 zeolite.By optimizing the amount of C_16-6-6 and C_16-3,the thickness of the layered zeolite was reduced from50nm to 2～4nm,the specific surface area and mesopore volume were increased,and the catalytic lifetime of methanol-to-propylene（MTP）reaction was also increased significantly.This work shows that the synergistic crystallization of the two templates can effectively adjust the morphology and pore structure parameters of the synthesized ZSM-5 zeolite nanosheets,in the meantime,the synthesis cost is also greatly reduced.Secondly,the effects of crystallization conditions and the additive in the synthesis of the hierarchical ZSM-5 zeolite with TBAOH and TPAOH as structure-directing agents were studied.The detailed characterization shows that the addition of the additive makes the solid yields of the hierarchical ZSM-5 zeolite synthesized with TBAOH and TPAOH as templates increase from 52.4%and 65.1%to 86.9%and 81.2%,respectively.The composition structure,crystal morphology and pore structure of the hierarchical ZSM-5 zeolite are comparable to the reference samples.The additive not only greatly improves the solid yields of the hierarchical ZSM-5 zeolites,but also greatly reduces the synthesis cost.Finally,a series of the hierarchical ZSM-5 zeolites were prepared using macroporous resins as the hard template agents.The study found that the hierarchical spherical ZSM-5 zeolite with a specific surface area of 650m²g^-1 could be synthesized in one step by using the nonpolar macroporous resin.While,the hierarchical ZSM-5zeolite with a pore volume of 1.34cm³g^-1 could also be synthesized by using the polar macroporous resin,however,it needs two steps crystallization,and the resulting hierarchical ZSM-5 zeolite has an ultra-high specific surface area of 1022m²g^-1.