Fabrication And Catalytic Application Of Hierarchical Structured Zeolite Materials

Zeolite molecular sieves are widely in the fields of adsorption, separation and catalysis due to their uniform and ordered micropores, large specific surface area, high hydrothermal stability and easily adjustable surface characters. However, the intrinsic molecular-sized micropores of zeolite have diffusion limitations on the chemical reaction rate as well as catalytic performance, especially in catalytic reaction of liquid phase or concerning with heavy molecules. In this case, the catalyst presents high reaction temperature and fast deactivation, sometimes low selectivity for aimed products.Recently, hierarchical porous zeolite materials based on nanozeolites have been attracted considerable research enthusiasm. Such materials not only inherit excellent acidity and hydrothermal stability of zeolite, but also facilitate the diffusion of reactant/product in bulky molecule-involved and/or diffusion-controlled catalytic reactions due to the insertion of meso- and/or macro-porosity and short microporous diffusion channel. Reasonally, they show unique properties in catalytic reactions, such as preferential selectivity to products, high activity, and long lifetime.Zeolite is conventionally obtained in fine powder. As in the case of industrial catalysis, a certain amount of binders are generally used for cementing zeolite crystals into large sticks or granules with mechanical stability. However, the inorganic binders may dilute the active zeolite and partially block the pore system, which give rise to diffusion limitation and inaccessibility of the active species. To overcome these problems, continuous progress is made on the mechanical stable zeolite monoliths with both uniform shape and hierarchical structure. Such monolithic zeolite material facilitates not only practical preparation and application, but also reactant/ product diffusion as well as reaction efficiency. As one of such typical structures, binderless zeolites without inert binders have high zeolite content and show excellent physichemical properties. Furthermore, binderless zeolites with hierarchical porosity of micro/meso/macropores offers perspective as an efficient catalyst in zeolite catalysis for its improved transport properties.Based on the research status and problems of zeolite materials, this thesis mainly focuses on the synthesis of hierarchical porous zeolite materials (including nanozeolites) and binderless zeolites. Meanwhile, the catalytic performances of the as-synthesized materials are also involved in the detailed work. Potentially the routes demonstrated in this thesis could expand the methods for fabrication of hierarchical porous zeolite materials and offer new strategies for industrial zeolite catalysts with high activity. The research work is categorized and discussed in seven chapters of this thesis.Chapter 2 involves the preparation of nanosized ZSM-5 zeolite using seeding director. In this chapter, nanosized ZSM-5 Zeolite was successfully prepared by hydrothermal synthesis with adding the prepared seeding director. The influences of the seeding director, crystallization temperature and the silica/alumina ratio of the synthesis gel were investigated. It was concluded that using seeding director in the hydrothermal preparation of ZSM-5 zeolite could decrease the template dosage, shorten the crystallization time and gain nanosized ZSM-5 zeolite. The crystal size of the resulted nanosized ZSM-5 zeolite is found to decrease with decreasing crystallization temperature and increasing alumina content in the synthesis gel.Chapter 3 discusses the hierarchical structured ZSM-5 zeolite of oriented nanorods and its performance in the alkylation of phenol with isopropanol Hierarchical structured ZSM-5 zeolite of c-axis oriented nanorods has been prepared by a zeolite-seeds assisted hydrothermal synthesis method without adding any type of mesoscale template. The final product has higher mesopore volume and external surface area than the sample prepared conventionally. Due to the shortened microporous channel and opening mesopore, the prepared HZSM-5 catalyst presents high catalytic activity and stability for the alkylation of phenol with isopropanol.Chapter 4 studies shape-controlled synthesis of monolithic ZSM-5 zeolite with hierarchical structure and mechanical stability. Columned ZSM-5 zeolite monoliths with hierarchical structure and excellent mechanical strength were successfully prepared by a hydrothermal transformation method. The intra-particle hollow structure formed during hydrothermal synthesis was attributed to the digestion of inner?zeolite accompanying with the growth of ZSM-5 zeolite shell. The obtained hierarchical ZSM-5 zeolite monoliths showed superior catalytic performance in?-pinene isomerization for their proper acidity and good diffusion, compared with the ZSM-5 zeolite sample prepared from the precursor without?zeolite.Chapter 5 involves the preparation of binderless utrafine ZSM-5 zeolite monoliths by vapor-phase transformation method. Using vapor-phase transformation method, binderless monoliths of ultrafine ZSM-5 zeolite crystals was prepared by conversion of the preformed bodies of diatomite and silica sol, which mixed with some zeolite seeding directors. The prepared materials possessed enriched porosity, high surface area, good mechanical strength and tunable acidity which was verified by the characterizations. The products have promised applications in catalyst and adsorbent.Chapter 6 studies production of BTX aromatics by catalytic hydropyrolysis of heavy pyrolysis gasoline. In this chapter, the catalyst was thoroughly studied for hydro-upgrading pyrolysis gasoline to produce light aromatics and light alkanes. An optimized bifunctional catalyst comprising metallic Pt supported on a binderless ZSM-5 zeolite showed significantly improved catalytic property for this reaction with both excellent stability and activity. The reported catalytic process produces a BTX mixture with low ethylbenzene content, LPG and fuel gas from heavy pyrolysis gasoline.Chapter 7 studies the catalytic hydropyrolysis of heavy reformates over binderless Pt/HZSM-5 zeolite. Effects of temperature, ratio of hydrogen to oil, reaction pressure and space velocity of heavy reformates on the reaction were systematically investigated as well as proper process conditions were optimized. At the optimized process conditions, the catalyst possesses very good stability during its life-testing experiment and is able to converted heavy reformats to above 58% yield of BTX aromatics with over 70% conversion of C9 and 50% conversion of C10+, respectively. And the remainder after the separation of BTX aromatics enriched trimethylbenzene (TMB), from which the TMB isomers could be obtained by fractionation. The reported process could convert low valuable heavy reformats to high valuable BTX and TMB aromatics, which offered a new route for treating heavy reformats in large scale.Chapter 8 discusses selective amination of ethylene oxide for preparation of ethanolamine over HZSM-5. TPD, FTIR and catalytic performance showed that HZSM-5 was more active than the sodium form. Relative selectivity of product was mainly controlled by the crystal size of ZSM-5. Surface modification such as silyation or rare earth oxide supporting was effective for enhancing the shape selectivity. Finally, La2O3 modified binderless HZSM-5 zeolite in small crystal size was introduced to the amination of EO in liquid phase, which showed a high selectivity of MEA and DEA and a long-term stability.