| The bi-quaternary ammonium template has a rich structure and higher skeleton charge density characteristics, it has shown a unique oriented advantage in the synthesis of a new multi-dimensional zeolite, and has become a research field for a new type of zeolite synthesis.The EUO-and ATO-type zeolites have one-dimensional pore channel and 12-membered ring characteristics, the zeolites with such a structure have higher thermal stability and larger specific surface area. Furthermore, they exhibit higher activity and para-selectivity in aromatic hydrocarbon catalytic conversion, and thus they are desirable shape-selective catalysts in xylene isomerization reaction. In this study, from the point of view of materials synthesis, the heteroatomic zeolites with EUO and ATO-type skeletons have been in-situ synthesized in a bi-quaternary ammonium template system. The synthesis process conditions and synthetic route of heteroatomic microporous zeolites have been also modified and optimized. Ultimately, the in-situ synthesized zeolite catalysts have been attempted to apply in the heterogeneous reactions of industrial raw oil, so that the modulation for ethyl benzene and p-xylene as the main products can be achieved.Using transition metal elements to isomorphously substitute silicon and aluminum elements in zeolites is an effective way to change the physicochemical properties of zeolite catalysts materials. With the aid of hydrothermal methods, we use the self-made bi-quaternary ammonium salt (hexamethonium bromide) as a template to synthesize EU-1 zeolite with EUO skeleton by doping with miscellaneous atoms (B, Fe, Co, Ni, La, Ce, etc). Meanwhile, using the self-made bi-quaternary ammonium alkali (hexamethonium) as a template, we also synthesize AlPO4-31 aluminophosphate (P-Al) zeolite with ATO skeleton by doping with miscellaneous atom (Mg). This thesis is mainly focused on the object of zeolite materials to study the synthesis conditions of miscellaneous zeolite, the physicochemical property of zeolite, the bonding state of miscellaneous atoms in the skeleton, the crystallization kinetics and catalytic reactions, especially in the Si-Al system using bi-quaternary ammonium salt as a template and in the P-Al system using bi-quaternary ammonium hydroxide as a template, respectively.In this study, considering the higher raw material costs and the longer crystallization time, the hydrothermal method is applied to solve the problems in the synthesis of EU-1 zeolite. By doping B atom, the B-A1-EU-1 boron-silicon-aluminum zeolite with high crystallinity can be synthesized in a shorter time in the alkaline system. The alkali and boric acid in the boron-silicon-aluminum sol system are easy to form tetraborate B(OH)4 tetrahedral configuration, which can easily combine with silicon tetrahedral to form zeolite unit, this will be beneficial to generate zeolite with a high degree crystallinity and to shorten its synthesis time. By using XPS to detect the changes of electron binding energies of boron atom Bls and silicon atom Si2p as well as oxygen atom Ols, we find that they have a synchronous change towards low-energy direction, which indicates the enhanced covalent bond and shortened bond length of B-O. This is consistent with the tendency of the volume decrease of B-A1-EU-1 zeolite unit cell.Through a fitting curve determined by kinetic experiments, it has found that the detected apparent activation energies of the nucleation (En) and growth (Eg) of A1-EU-1 zeolite doped with B atom have decreased to 21.50 kJ/mol and 30.48kJ/mol, respectively. This further verifies that introducing heteroatom-B can promote the formation and growth of EU-1 zeolite nuclei. In addition, the catalytic reaction experiments show that B-A1-EU-1 zeolite containing boron has a higher selectivity for p-xylene in the isomerization reaction of reformed gasoline, which is basically stable around 23.1%; and the conversion rate of ethylbenzene is about 41%. This also confirms that the boron doping plays a certain role in increasing the catalyst activity.In view of the higher catalytic activity of rare earth metals on the cracking of hydrocarbon molecules and isomerization reactions, it is possible that the rare earth metals and EU-1 zeolite have a synergetic catalytic effect in ethylbenzene conversion and p-xylene isomerization reaction. Using bi-quaternary ammonium salt as a template, we develop and optimize the synthesis for a new type of 10- and 12-membered rings EU-1 zeolite doped with rare earth metals, and further investigate some phenomena caused by doping rare earth metals into zeolite, such as:the deformation of silicon aluminum oxygen tetrahedron, and the volume expansion of La-Al-EU-1 zeolite unit cell, as well as the presence of four-coordinated La3+ ion. By comparing the effects of Lanthanide ions doping (Ln:La, Ce, Nd, Sm, and Gd) on EU-1 zeolite, we have found that when rare earth metal ions have the same charge, with decreasing the radius of Lanthanide ions, the coagulation capacity of the ions increases; the destructive effect on the surface charge of synthetic liquid sol also increases, thus the crystallinity of the synthetic sample decreases, and the unit cell volume for forming zeolite reduces as well. Catalytic reaction shows that when EU-1 zeolite doped with rare earth metals is applied in the isomerization reaction of reforming gasoline, it can significantly decrease the yield of the side reactions. The p-xylene selectivity of La-Al-EU-1 zeolite is higher than that of Ce-Al-EU-1.The oxysalts of iron-based elements play two roles (doping and promoting) in the zeolite crystallization reaction, not only they can shorten the crystallization time, meanwhile can increase the catalytic reaction activity significantly. The growth promotion of EU-1 zeolite by iron-based nitrate is the result of the interaction between cationic and anionic. The empty d-orbitals of iron, cobalt, and nickel cations can accelerate the formation of silicon oligomer, and such a structure can accelerate the nucleation and growth of the crystals in the crystallization process. The XAFS results show that with the crystallization process going on, the amorphous sample firstly forms a tetrahedral coordination of metal-silicon-oxygen structure. With the completion of the crystallization, four-coordinated structural units are gradually transformed into a tetrahedral coordinated iron-silicon-oxygen skeleton, in which iron-silicon-oxygen ionic structural unit is also transformed into skeleton iron species with a tetrahedral covalent bonding structure.From the curve fitting of the kinetic experiments, it shows that the apparent nucleation activation energy (En) of Al-EU-1 zeolite doped with Co, Ni and Fe atoms is greater than the apparent growth activation energy (Eg) of its, which indicates that the nucleation process is the rate controlling step for the crystallization. In the isomerization reaction of the reformed gasoline, using Fe-Al-EU-1 zeolite containing iron can significantly reduce the yield of the side reactions and increase the conversion rate of ethylbenzene. Thus, iron doping plays a certain role in the improvement of the catalyst property.For the purpose of exploring the role of bi-quaternary ammonium base as a template in the synthesis of aluminum phosphate microporous zeolite, through controlling the synthetic conditions and selecting different types of templates, we investigate the synthesis of the pure phase hexagonal Mg-APO-31, and find that the bi-quaternary ammonium base template has a good orientation for ATO AlPO4-31 aluminophosphate and heteroatom-containing aluminophosphate Mg-APO-31 zeolite. Besides, the amount of the template used in the experiments is only one third of normal requirement. Experimental results show that the cell parameters of the hexagonal Mg-APO-31 are greater than those of AlPO4-31. The mixed crystals of SAPO-5 and SAPO-31 can be obtained when doping Si into AlPO4-31 aluminophosphate zeolite containing ATO skeleton. High ratio of n (SiO2)/n (Al2O3) is favorable to produce SAPO-5, while low ratio is conducive to generate SAPO-31. |
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