Synthesis, Characterizations And Catalytic Applications Of Integral-structured Spherical Zeolites

Zeolites were widely used in chemical industrial processes by virtue of its unique structure and excellent catalytic properties. Conventionally, hydrothermally synthesized zeolites are of fine powder materials which need further molding processing to meet the standards in industrial catalysis applications. The traditional molding methods generally mix zeolite powders with inorganic binders (colloidal silica, clay, etc.) to acquire satisfactory particle shapes and sizes, unfortunately, the introduced binders inevitably bring about a great many negative effects, pore plugging and active site poisoning, for example, which would undoubtedly lead to reduction of catalytic efficiency. Herein, the dissertation focuses on exploiting some molding technologies in the absence of inorganic binders, in the meantime, aiming at the synthesis of integral-structured spherical zeolites. Basically, two methodologies, microemulsion-based synthesis and mother liquid-based assembly, are employed here, mainly in the following three specific parts orienting around Ti-MOR and TS-1.In first part, integral-structured micro/mesoporous spheres (MMSM), the self-assembled composite of mesoporous silica phase and Ti-containing mordenite (Ti-MOR) zeolite crystals, were synthesized through an oil-in-water microemulsion acidic system, involving tetrabutyl orthosilicate as silica source and cetyltrimethylammonium bromide as template and aluminum sulfate as additive. This research presented a novel and versatile technique for preparing a integrally structured liquid-phase oxidation catalyst with a tunable particle dimension (250-720 μm) and a changeable mass ratio of active component Ti-MOR to mesosilica (0.78-2.33). Porosity analysis indicated that the composite materials possessed the connatural microporosity of zeolite and the disordered mesopores (5.41 nm) in silica part. The whole formation process of MMSM was real-time tracked with an optical microscope. With a special focus on the importance of aluminum sulfate additive in the microemulsion synthesis of composite microspheres, a possible formation mechanism has been proposed, in which double electrostatic interactions played the crucial role of in mediating the mesosilica species and zeolite crystals. The obtained MMSM materials were hydrothermally stable and showed significantly enhanced catalytic activity in the liquid-phase ammoximation of cyclohexanone in comparison to the parent Ti-MOR powder.In second part, integral-structured micro/mesoporous spheres (MMSS), the self-assembled composite of mesoporous silica phase and TS-1 zeolite crystals, were synthesized through an oil-in-water microemulsion alkalic system, involving cetyltrimethylammonium bromide, tetrabutyl orthosilicate, n-butanol, tetramethylammonium hydroxide and deionized water. The content of micropore zeolite in the composite spheres is controllable, as the TS-1/SiO2 mass ratio increases from 0.351 to 1.564, the spherical particle size could vary in the range of 340-1150 μm. As the experiment results indicated, catalytic activities of the obtained MMSS materials were barely satisfactory, which were slightly lower in comparison to the TS-1 industrial powder in the 1-Hexene epoxidation.In third part, relatively ideal integral-structured mordenite spheres were synthesized in conventional crystallization mother liquid of mordenite with triblock copolymer F127 or P123 introducing into the synthetic system, followed by dealumination and titanium-planting process we obtained Ti-MOR microspheres of 5-15 μm. According to the experimental facts, integral-structured mordenite spheres have met the standards of industrial catalysts in the aspects like morphology, dimension, stability and mechanical strength, however, its catalytic properties were still much inferior to Ti-MOR industrial sample.