Organic Template-Free Syntheses Of Zeolites And The Preparation Of Porous Particles Assembled From Zeolite Nanocrystals

Zeolites, especially large pore zeolites, have been widely applied in many industrial technologies, including gas adsorption, ion exchange, separation, and catalysis for their unique porosity and high surface area, which attract extensive studies on the influence of composition, temperature, and environment on the synthetic process of zeolites. Aluminosilicate zeolites are widely used in the petroleum catalysis and refining industry, and most of the applications require the zeolites with a low cost and friendly to the environment. Notably, modern synthesis methodologies for preparing zeolites or zeolite-like materials typically involve the use of organic molecules that direct the assembly pathway and ultimately fill the pore space. The use of organic template has obvious disadvantages such as relatively high cost of organic template and the harmful gas produced during the removal of the template normally carried out by high temperature combustion.The former project majors in the organic template free synthesis of aluminosilicate zeolites, and the methods include adjusting the compositons of the starting gel, especially the ratio of Na2O/SiO2 and the method of adding zeolite precursor solutions to introduce the primary or secondary building units, which could direct or effect the growth of zeolite. Large-pore aluminosilicate zeolite of ECR-1 is an intimate twin of the mordenite-like sheets between layers of mazzite-like cages, which is firstly discovered by Leonowicz and Vaughan using the organic template of bis-(2-hydroxyethyl)dimethylammonium chloride. Later, ECR-1 is successfully synthesized in the presence of adamantine-containing diquaternary alkylammonium iodides and very recently with the organic template TMA+. In these cases, organic templates in the synthesis of ECR-1 are necessary. However, these organic templates with relatively high cost in the synthesis severely hinder the practical applications of ECR-1 in catalytic reactions for petroleum industry.Zeolite MOR and zeolite MAZ, however, could be successfully synthesized in the absence of organic template. Zeolite ECR-1, an intimate twin of the mordenite-like sheets between layers of mazzite-like cages, should also be able to be synthesized without any organic template. By carefully adjusting the molar ratio of Na2O/SiO2 in the synthesis, large pore aluminosilicate zeolite of ECR-1 is successfully synthesized in the absence of organic template for the first time.Another successful example is aluminosilicate zeolite of ZSM-34, which is an intergrowth of OFF and ERI zeolites containing zeolitic building units of cancrinite (CAN) cages, which is known to be a good catalyst for the conversion of methanol to C2-C5 olefins with high selectivity for ethylene. ZSM-34 zeolite was firstly discovered by Rubin et al using organic template of choline [(CH3)3NCH2CH2OH], and later ZSM-34 samples were successfully synthesized in the presence of different diamines (NH2CnH2nNH2, n=4, 6, 8, 10). In these cases, organic templates are necessary. However, these organic templates with relatively high cost in the synthesis severely hinder the practical applications of ZSM-34 zeolite in catalytic reactions. Both zeolite offretite and erionite could be synthesized in the absence of organic template, so ZSM-34, the intergrowth of the two zeolites, should be able to be synthesized in the absence of organic template. In our process, from an assistant of zeolite L seeds solution, zeolite ZSM-34 was successfully synthesized in the absence of organic template for the first time.Another project of the thesis is majoring in the assembly of nanocrystals of zeolite for the use of catalysis. There is of great interest for preparation of zeolite nanocrystals because the decrease in the crystal size results in high external surface area, fast diffusive rate, and much exposed active sites. Nanocrystals of zeolite give high catalytic activities and high selectivities, while the preparation of nanocrystals of zeolite is quite a complex process compared with common zeolites. A large amount of industrially used zeolites with micrometer-sizes are normally obtained by a filtration route, which has advantages such as high yield of the solid product and easy separation of zeolite crystals from a slurry system. Usually, zeolite nanocrystals are obtained from high-speed centrifugation in slurry system, which is difficult to prepare a large amount in industry.To overcome the problems for the preparation of zeolite nanocrystals, couples of novel routes for synthesis of zeolites with fast mass transfer in catalytic reactions have been reported. Zeolite nanocrystals could be assembled under the structure formed by polystyrene, mesoporous zeolite templated by resin, nanosized carbon, silane-functionalized polymer porogen, organic-inorganic hybrid surfactant, and cationic polymer et al. The industrial applications of these mesoporous zeolites, however, are still limited by the complexity of their synthetic procedures.An alternative and simple route in the thesis is given for one-pot synthesis of stable, porous, and bulky particles with high external surface area and large pore volume from self-assembly between zeolite nanocrystals and mesoscale cationic polymers with high charge density. Very importantly, these particles with high solid yield could be easily separated from a filtration. Catalytic alkylation of benzene with isopropanol shows that these bulky particles exhibit similar activity and selectivity to zeolite nanocrystals. Obviously, these zeolite bulky particles combine advantages of both the nanocrystals (high external surface area, large mesopore volume, and fast diffusive rate) and the micrometer-sized crystals (easy filtration and high solid yield). The third project is majoring in the synthesis of zeolites in the presence of new template, which is synthesized by myself. As we know that zeolites as solid acids are widely used in the catalytic industry and refining industry, and they show good activities and selectivities in some reactions. The small channels of the zeolites, however, prohibit the application of the zeolite in the industry, especially for the catalysis of large molecules. Considering the question of mass transfer, tridimentional large pore zeolites are of interests for the material scientists, While such zeolites are only Y, BEC, ITQ-7, and ITQ-21.As far as we know, only one template of N-methylsparteinuium hydroxide could be used for the synthesis of the zeolite ITQ-21. While the research of new templates for the synthesis of zeolites, especially the tridimentional large pore zeolites, are of great interests for the scientists. If it happens that the only one organic template is no longer supplied or prohibited for some reasons, new template is urgent for the synthesis of the zeolite, and this has been taken place for the synthesis of zeolite ITQ-7. Herein, new template is synthesized for the synthesis of zeolite, and zeolite ITQ-21 is successfully synthesized by using the new template in the presence of F- anion and germanium.