Construction And Catalytic Property Of HSZ Materials With Highly Exposed Lewis Acid Sites By Heteroatom Implantation Into Hierarchical Zeolite Framework

The emergence of“symbiotic”zeolite had given the special property of microporous zeolites,which is usually formed from the disordered accumulation of the same structural units to form a cage structure.This special cage is contributed to the emergence of the mesoporous structure,so as to make the microporous zeolites retain its good stability and have the advantages in transfer and diffusion of complex channel structures,which not only effectively increases the contact area of macromolecular reactant with the catalytic active center in reactions,but also improves the diffusion property of microporous zeolites.Based on HSZ hierarchical porous zeolites,the construction and catalytic performance of new solid acid catalytic zeolites have been systematically studied in this thesis.The specific research contents are as follows:(1)A highly exposed Lewis solid acid catalyst Zr-HSZ-K was successfully constructed in situ by K⁺-assisted one-step rotational hydrothermal method on the theoretical basis of HSZ material with unique hollow nest structure which was formed by single/double/multilayer MWW(framework type code)nanocrystals.This is the first report to use potassium-induced method to combine the heteroatomic Zr with the hierarchical porous HSZ(Hollownest-Structured Zr-zeolite)zeolite framework.We examined the various factors that influenced the synthesis in detail.By using the characteristic of the special lamellar structure and rich hydroxyls on the surface of HSZ zeolite,the highly exposed and isolated Zr⁴⁺open active site((Si-O)₂-Zr=O)of the introduced zirconium species was formed in the form of tetra-coordination on the highly exposed crystal surface of the zeolite.The special lamellar structure and the highly dispersed and isolated Zr⁴⁺open active site enabled the substrate molecules to efficiently transfer and diffuse,so as to effectively improve the efficiency of the catalytic reaction process while retaining the high catalytic activity.(2)Different synthesis methods were used to introduce zirconium species to the active sites of zeolite on the surface acidity after zeolite modification were compared in the preparation of Zr-HSZ zeolite.By using the hierarchical porous structure which looks like a microreactor,the Zr-HSZ catalyst had excellent catalytic performance in the Prins condensation reaction of?-pinene and paraformaldehyde.The catalytic performance of Zr-HSZ synthesized by different methods in Prins condensation reaction is quite different,indicating that the highly effective catalytic activity is closely related to the external specific surface area,surface acidity and other factors of the material.(3)The factors influencing the introduction of stannum species and the reaction conditions of Prins condensation of?-pinene with paraformaldehyde were investigated.The results showed that the addition of a small amount of basic template in the post-synthesis solution could help more stannum species to combine with the defect sites of zeolite framework,and the synthesized solid acid catalyst had excellent catalytic activity for Prins condensation of?-pinene/paraformaldehyde.(4)Considering the favorable influence of alkali metal salts for one-step hydrothermal synthesis of solid acid catalyst,V-HSZ zeolite was constructed in situ by changing the content of Vanadium species and adding different types of alkali metal salts,and the catalytic performance of the as-synthesized Lewis solid acid catalyst was investigated.The researches showed that the effects on the morphology,layer stacking,surface acidity and catalytic performance of the synthesized samples were different with different alkali metal salts added in the gel precursor.(5)The“interbedding”of zeolite was realized by adding different content of macromolecular organic agent dicyclohexamine(DCHA)to the gel precursor.Using different physicochemical characterization methods and allyl chloride epoxidation as the probe reaction,it was observed that the addition of different contents of DCHA in the gel precursor could effectively change the morphology of HSZ zeolite and the size of disordered stacking MWW nanosheets.This was conducive to the expansion of the interlayer and realized the“calcination-free”concept of layer-structured zeolite,which also verified that the“interbedding”method of layered zeolite was feasible for realizing the concept of“calcination-free”.