New Routes For Synthesizing Of Zeolites

Nowadays, how to use the existing energy based on oil, natural gas and coal in amore efficient way and develop new resource including solar and biomass energy insuch a resources diminishing circumstance are the emerging problems we faced. Inthe mean time, environmental protection is a key step for the sustainabledevelopment of the world. Currently, zeolites with stable, uniform and intricatemicropores as well as good shape selectivity are regarded as one of the mostimportant heterogeneous catalysts for solving problems of the energy andenvironment.It is of great importance to develop facile, green and low-cost routes ofsynthesizing zeolites. And fully understanding of their growth process will behelpful for rationally designing new structures and effectively developing newproperties.Based on the above background, this thesis was devoted to developing of newsynthesizing routes and investigating zeolite crystallization mechanism.About developing of new synthesizing routes, we have done these work:Designing novel templates for one pot synthesis of Cu-SSZ-13;Organotemplate-free and one-pot fabrication of nano-rods assembled MOR; Solidothermal synthesis of zeolites from solid raw materials in the absence ofsolvent.SSZ-13with CHA cages connected by small8-ring pore openings is active andselective for methanol-to-olefin (MTO) reaction. In addition, recent reports alsoindicate that Cu-SSZ-13is an active catalyst for selective catalytic reduction (SCR)of NOx with NH3.But controlling of Cu loading in SSZ-13zeolite is not easy, dueto the small pore openings and limitation of ion-exchanged capacity. Additionally,relative high cost of the template N,N,N-trimethyl-1-1-adamantammoniumhydroxide (TMAdaOH) strongly limits wide applications of SSZ-13zeolite.Therefore, it is strongly desirable to synthesize Cu-SSZ-13with controllable metalloading using low-cost templates.We rationally designed a low-cost copper-amine complex (Cu-TEPA) as anefficient template for one-pot synthesis of Cu-SSZ-13zeolites with changeableSi/Al ratios. Cu-TEPA has a large lgK suggesting that it has a good stability instrongly alkaline media. Proper geometry and appropriate size make this complexfits well with CHA cages as an effective template. The products with high coppercontent and good dispersion of copper species exhibit superior catalyticperformance in NH3-SCR reaction, which is potentially important for the abatementof environmentally harmful NOx compounds. And this novel route is helpful forsynthesis of new type of zeolites.It is well known that hierarchical structured zeolites show advantages in masstransferring and diffusion in many catalytic reactions. Two strategies were used indesigning hierarchical zeolites which are using organic mesoscale templates andpost-treatments. The organotemplation has increased the cost of zeolite products andbrought environment problems, and the use of post-treatments such as steaming andleaching normally results in the reduction of zeolite crystallinity. Is there any waywhich can combine both organic-template free method and with no post-treatment?According to the above assumption, we designed an alternative one-potorganotemplate-free route for synthesizing hierarchical structured MOR zeolite inthe presence of MOR seeds solution. In this process, neither organic templates nor post-treatments are involved. The hierarchical zeolite structure comes from thealigned arrays of MOR nano-rods. The voids between the nano-rods provide spaceswhich are favorable for the mass transfer, and the relatively bulky MOR particlesare very convenient for filtration. Interestingly, this route is also successful tointroduce catalytically active iron species into MOR zeolite.The addition of MOR seeds solution remarkably improved the crystallizationrate, giving the preferential growth of crystals along with the c-direction. Theoriented growth of MOR crystals is attractive for fabrication of advancednanomaterials.Normally, zeolite syntheses require the presence of solvents from variousmethodologies such as hydrothermal, solvothermal, and ionothermal routes. The useof a large amount of solvents is costly and energy-consuming. Therefore, theavoidance of solvents in the zeolite syntheses is strongly desirable.We demonstrate a simple solidothermal synthesis of zeolites from solid rawmaterials in the absence of solvents. Compared with hydrothermal route, thissolidothermal synthesis not only significantly reduces the production of pollutedwastes but also greatly increases the yield of zeolite products. In addition, the use ofstarting solid raw materials remarkably enhances the synthesis efficiency. Forindustrial production of zeolites, the solidothermal synthesis in the absence ofsolvents means significant savings in raw materials, energy, and costs.We have shown the successful syntheses of ZSM-5, Silicalite-1, ZSM-39, SOD,MOR, Beta, and FAU zeolites from the solidothermal route. Also, this route can besuccessfully applied to synthesis of hierarchical structured zeolites.Zeolite synthesis mainly involves the formation of zeolite precursors, nucleation,and crystal growth. Full understanding of the crystallization and the mechanism ofzeolites formation is highly necessary for rationally designing new structures andeffectively developing new properties. Despite of all the great efforts done, athorough understanding of the zeolite formation mechanism still remains achallenge due to the complexity of the zeolite synthesis. As a model for understanding zeolite synthetic mechanism, zeolite A has beenextensively investigated through many techniques because of its relatively simplestarting aluminosilicate gel in the synthesis, rapid kinetics for crystallization, andwide applications.In our thesis, the hydrothermal synthesis of Zeolite A was studied by UV Ramanand NMR spectroscopies. The results suggest that the crystallization of zeolite Amainly occurs in the solid phase including a large amount of D4R units, and liquidphase is not a critical factor. The importance of D4R units in the synthesis isconfirmed by successful conversion from D4R solution to zeolite A crystals.