Studies On The Synthesis And Performance Of The ZSM-11 And B-ZSM-11 Zeolites

Zeoltite ZSM-11 with idealized cell constants belongs to tetragonal, which has two-dimensional pore structure with intersecting straight channels. It is an important adsorbent and a good shape-selective catalyst. Both ZSM-11 and ZSM-5 belong to pentasil family and they have the similar structure. Therefore, the synthesis of zeolite ZSM-11 was usually a ZSM-11/ZSM-5 intergrowth, and that pure-phase ZSM-11 was quite difficult to prepare for many research workers. Up to now, synthesis of ZSM-11 zeolite has focused on using tetrabutylammonium(TBA) as structure-directing agengt (SDA) in hydrothermal system. In this dissertation, pure-phase ZSM-11 was synthesized using TBA and BTMAC1 as co-templates for the first time. The influences of OH^-/SiO₂ ratio, template, the content of water, crystallization temperature and crystallization time on the synthesis of ZSM-11 have been clarified elaborately. It is found that the TBA is an important SDA in synthesis of ZSM-11 zeolite, and the BTMAC1 is also indispensable for synthesizing perfect ZSM-11 zeolite.The in-situ solid-transformation method has some advantages that other methods don't have. It overcome some of the deficiencies of hydrothermal or nonaqueous synthesis. For instance, it can decrease the synthesis cost and improve the quality of products. In addition, This route can be considered as a friendly environment method for its no mother liquid exsists after the crystalization. So it is an ideal method for synthesis of zeolites. Therefore, in this dissertation, ZSM-11 zeolite was synthesized by in-situ solid-transformation method, which was compared with the traditional hydrothermal ways. Also the formation of the pure ZSM-11 is affected by many synthesis factors. The experimental results showed that the product was well crystallized even when the H₂O/SiO₂ molar ratio of the raw materials was lowed at 3. However, water is necessary to transfer heat and mass for synthesize zeolite ZSM-11 by in-situ solid-transformation method. Moreover, NaF as the mineralizer can promote the crystal nucleation and make the crystallization of zeolite ZSM-11 easier.The exploiture of heteroatom-containing molecular sieves contributes much to the synthesis of the molecular sieves and the field of catalysis. Zeolites can have some special catalyst abilities for the incorporation of activity atoms of other elements in the framework position. Therefore, much attention has been paid to the heteroatom-containing molecular sieves in recent years. The heteroatom-containing zeolite ZSM-11 is one of the hotspots. Therefore, pure-phase B-ZSM-11 zeolite with high crystallization has been synthesized by using co-templates. The results of kinds of characterization showed that the boron was incorporated in the framework. The experimental results showed that the Na₂O/SiO₂ ratio of the raw materials in synthesis of B-ZSM-11 zeolite was wider than that of ZSM-11 zeolite. And the Na₂O/SiO₂ ratio needs to be increased if more boron should be incorporated into the framework of the ZSM-11 zeolite. At the same time, B-ZSM-11 zeolite was synthesized by in-situ solid-transformation method, which was compared with the traditional hydrothermal ways. As a result, the cell constants of B-ZSM-11 zeolite is obviously smaller than ZSM-11 zeolite. And the sample synthesized in the solid system is a little bigger than that synthesized in the hydrothermal system.Nanosized zeolites have large external surface, high surface energy and shorter channels as compared with the microsized zeolites. They are particularly suited for catalysis applications. The reduction of the particle size of zeolites from the micrometer to the nanometer scale can improve the mass- and heat-transfer in catalytic and sorption processes, enhance their activity, catalytic selectivity, ability of resisting coke formation and prolong their lifetime in some catalytic reactions. Therefore, nanosized ZSM-11 and B-ZSM-11 zeolites with average particle size less than 10nm have been synthesized successfully in this dissertation, which were characterized by X-ray diffraction, dynamic light scattering(DLS), IR, N₂ adsorption/desorption. The factors that influence particle size are also discussed, such as the ratio of the raw materials and the crystallization time. The results indicate that the addition of NaOH and EtOH can effectively minish the particle size. And prolonging crystallization time leads to a considerable increase of the radius of the crystallites.