The Studies On Synthesis And Characterization Of Zeolite MCM-22 And Its Delaminated Zeolite ITQ-2

Zeolite MCM-22, with both 10 and 12 member ring pore, high thermal/hydrothermal stability and excellent performance in several catalytic reactions, is a very distinctive catalytic material. So far, researchers have done a great deal of studies on zeolite MCM-22, and zeolite MCM-22 has been synthesized by several different method. However, the synthesis of zeolite MCM-22 meet some limitations, such as high synthesis cost, long reaction period and low productivity. Therefore, In this dissertation, zeolite MCM-22 with pure phase and good crystallinities have been prepared successfully under low n(H₂O)/n(SiO₂) ratio, which were called the extremely dense system. The influences of n(OH)/n(SiO₂) ratio, the content of water and template, crystallization temperature and crystallization time on the synthesis of zeolite MCM-22 have been clarified elaborately. In contrast with the synthesis of zeolite MCM-22 under the condition of high n(H₂O)/n(SiO₂) ratio, the synthesis of zeolite MCM-22 in extremely dense system has some advantages, such as simple operation, wide synthesis region, low consumption of NaOH, HMI and H₂O, and high productivity. In addition, zeolite MCM-22 obtained from this system had higher crystallinities than those prepared under high n(H₂O)/n(SiO₂) ratio. Correspondingly, its BET surface area and micropore volume increased. Compared with the synthesis conditions given in literature, this method could decrease the consumption of HMI and NaOH effectively, which was beneficial to the reduction of synthesis cost and the protection of environment.Originally, zeolite MCM-22 was prepared by dynamic hydrothermal synthesis. There were some deficiencies with traditional dynamic hydrothermal synthesis in producing zeolite MCM-22, such as great consumption of HMI and long period of crystallization, etc. In this dissertation, by lowering n(H₂O)/n(SiO₂) ratio properly, adding aging process during synthesis and increasing crystallization temperature, crystallization period of zeolite MCM-22 could be reduced successfully to less than 3 days. The consumption of NaOH and HMI could also be decreased. Consequently, the efficiency of zeolite MCM-22 production has been improved greatly. The experimental results showed that the nucleation of zeolite MCM-22 was much more easy under rotating conditions than under static conditions. There were two possible reasons for this phenomenon. At first, rotating conditions could promote the silica dissolution and made reaction mixture more homogeneous, which led to easier nucleation of zeolite MCM-22. In the meanwhile, under rotating conditions, higher n(NaOH)/n(SiO₂) ratio and n(HMI)/n(SiO₂) ratio of reaction mixture may be another reason which made zeolite MCM-22 nucleate much more easily.Delaminated zeolite was prepared by swelling and exfoliating the lamellar zeolite precursor. Its structure consists of monolayer structure of precursor. Delaminated zeolite, with an extremely high external surface area, combines the advantages of zeolite (strong acidity and high hydrothermal stability) and amorphous aluminosilicate (larger reactants nearly unrestricted access to the acid sites). In this dissertation, under proper producing conditions, ITQ-2 has been successfully prepared by swelling and exfoliating zeolite MCM-22(p) precursor using TPAOH and CTMABr as swollen reagent. The synthesized samples were characterized by XRD, IR, N₂ adsorption/desorption. The results indicated that layers of zeolite MCM-22(p) had been swollen and exfoliated successfully. These layers oriented randomly and stacked disorderedly, forming a lot of mesoporous in ITQ-2. There are a large amount of silanol groups on the external surface of ITQ-2. Compared with zeolite MCM-22, ITQ-2 has a larger mesoporous surface area and volume.