Synthesis, Characterizations And Catalytic Properties Of Integral-structured Zeolites

The dissertation is aiming at preparing integral-structured zeolites, obtaining shaped zeolite catalysts by one-step crystallization, enriching the methodology for the preparation of shaped catalysts. Three methodologies adopted herein are in-situ hydrothermal crystallization, zeolite nanoparticle self-assembly and dry gel conversion. They are employed to synthesize integral-structured zeolites of ZSM-5, MCM-22and TS-lwith promising applications in industrial processes.Firstly, we chose mesoporous silica spheres (MSS) as silica source, isopropylamine (iPA) as template to synthesize ZSM-5(MFI topology) by hydrothermal crystallization at443K, in the hope of obtaining ZSM-5spheres that replicate the shape of MSS. Fortunately, the shape of MSS did remain intact after being fully transformed into integral-structured ZSM-5zeolite spheres. Moreover, the ZSM-5zeolite spheres are of high crystallinity and possess unique hollow and core/shell structure. In order to clarify the forming mechanism, specimens at different crystallization stages were prepared and characterized. The in-situ transformation of MSS into integral-structured ZSM-5zeolite spheres follows a stepwise "surface to core" crystallization process. Before the inner part of MSS began to crystallize, the surface of MSS had already crystallized into ZSM-5zeolite shell, which later prevents the sphere from falling apart. Then the amorphous species in the core part moved towards ZSM-5shell and crystallized. Finally, integral-structured ZSM-5spheres with a hollow and core/shell structure formed by consuming all the amorphous species.Integral-structured ZSM-5zeolite spheres were synthesized by in-situ hydrothermal transformation of mesoporous silica spheres, can integral-structured zeolite spheres of other topologies be synthesized in the same way? The attempt to synthesize MCM-22(MWW topology) zeolite spheres was carried out using MSS as silica source and hexamethyleneimine (HMI) as template, and integral-structured MCM-22zeolite spheres were obtained following the same stepwise "surface to core" crystallization process. The obtained MCM-22zeolite was a strong solid acid as characterized by FT-IR and NH3-TPD, and exhibits similar catalytic property to conventional MCM-22powder.Then, we introduced triblock copolymer (F127or P123) into the synthetic system for crystallizing conventional TS-1(C-TS-1), aiming at one-pot synthesizing integral-structured TS-1aggregates with easy separation and industrial applications. With the assistance of surfactant, TS-1nanoparticles of50-100nm were self-assembled into integral-structured mesoporous microspheres which contained regular intercrystal mesopores in the range of6-10nm in addition to original micropores. The crystallite aggregating in microspheres did not collapse after ultrasonication for2h or refluxing in2M HNO3for20h. The high mechanical strength implied their potential applications in continuous slurry-bed reactors where an easy separation of solid catalyst from reaction mixture is required. M-TS-1-MS was comparably active to C-TS-1in pyridine oxidation,1-hexene epoxidation and ammoximation of cyclohexanone with H2O2as the oxidant, whereas exhibited a higher activity in the oxidation of bulky substrates such as3-picoline and cyclohexene due to the presence of mesopores.Finally, a dry gel was made using mesoporous silica spheres (MSS) as silica source, and mixed with titanium source and TPAOH. Integral-structured TS-1spheres were obtained by crystallizing the dry gel through vapor phase transportation. The obtained TS-1spheres were highly crystalline. Moreover, TS-1spheres with different sizes can be obtained by dry gel conversion from different sized MSS, which means the size of MSS has little effect on the crystallized TS-1spheres. So that dry gel conversion can be adopted to prepare integral-structured zeolite catalyst, and has great potential for industrial application.