Controllable Fabrication Of Macro And Mesochannels Using Hard-templating Method In Hierarchical HZSM-5 For Catalytic Cracking

Hierarchically porous zeolites?HPZs?are widely investigated for their good catalytic activity,stability and diffusion properties.The synthesis process of HPZs with hard templates is simple and can be specifically regulated.In this thesis,HZSM-5 HPZs with different porous structures were synthesized by modifying the structure of hard template.The catalytic cracking performance of the synthesized zeolites were further characterized using n-decane,methylcyclohexane and tetrahydrodicyclopentadiene?JP-10?as model compounds.The effects of morphology and dimension of pores on the catalytic cracking performance of zeolites were also investigated.HZSM-5 zeolites with one-dimensional open mesopores were prepared by using carbon nanotubes?CNTs?as the hard template.It was found that compared with the hydrothermal crystallization method,the dry gel method could not only maintain the Si/Al ratio and acidity of zeolite,but also improve the utilization ratio of CNTs.The effect of pore morphology on cracking was more significant for JP-10 that has a large molecularly dynamical diameter:the HZSM-5 with open mesopores exhibit significantly higher catalytic activity than those with closed mesopores.HZSM-5 zeolites with intracrystalline two-dimensional and interconnected mesopores were synthesized by using polypyrrole as the hard template.It was found that an appropriate degree of crosslinking was indispensible for the formation of HPZs.The conversion of JP-10 catalytic cracking increased from 25%to 41%due to the improved accessibility of acid sites.Zeoliteswithintercrystallinemacroporesandtwo-dimensionally monolish-structured materials were obtained via secondary synthesis on carbon fiber matrices.The monolish-structured materials showed high structural and catalytic stability.Compared with conventional catalyst,JP-10 cracking stability of the synthesized zeolite increased by nearly 100%.Hollow spheric HZSM-5 zeolites with a large-meso-micro hierarchically porous structure were synthesized by the seed-oriented self-dissolution effect of silicon and silica-alumina sphere as hard templates.The amount of acid was regulated by introducting Al in the synthesis procedure of silica sphere or in the following crystallization process.In the catalytic cracking reaction of JP-10,the activity and stability were improved for hollow spheric zeolites with higher aluminum content,and the yield of macromolecule product above C8 was increased.The reversible conversion of acid sites in the high temperature calcination process for removing hard templates was systematically studied.It was found that H₂O₂ or NH₄⁺treatment could significantly accelerate the recovery of dehydrogenated Br?nsted acid.Treatments with NH₄⁺increased the B/L acid ratio of zeolite from 0.5to 4.0,and thus increased the catalytic cracking conversion from 6%to 77%.