Rapid Synthesis Of Aluminosilicate Zeolites And Their Crystallization Mechanism Studies

Nowaday,with the rapid advancement in science and technology,has driven an increase demand in energy.However,the primary energy source today is still fossil energywith great concerns on its supply and the serious environmental problems it brings.Therefore,the development of new materials which allows efficient energy utilization and conversion and renewable energy sources are urgently demanded.With these in mind,the widely used porous materials which found essential applications in petrochemical,environmental protection,life sciences,medicine and other fields have attracted attentions.Zeolite materials are one of the most widely used porous materials due to their unique structural properties,diverse pore structure,ultra-high specific surface area and specific reactive sites.Zeolite is a crystalline microporous material composed of a regular network of alumina and silica tetrahedrons(TO₄-oxygen atoms bridge tetrahedral atoms).The modern synthesis of zeolite mainly relies on the silica-alumina sources,organic templates,and the addition of solvents.However,problems such as long synthesis time,low yield,and serious pollution are typically found in traditional synthetic methods.It is thus important to develop new synthesis approaches for efficient and low cost synthesis of the industrially important zeolite materials.This thesis is devoted to the new rapid synthesis route for zeolite,mainly focusing on reducing or eliminating the use of organic templates.The main advantages of the new synthetic route are high yield,shorter synthesis time,low cost,low organic template usage,low pollution,and simple and convenient operations.The work is focused on industrially important zeolites with CHA-,AFX-,MFIand AEI-type topologies with great potential in Methanol-to olefin(MTO)and SCR De NOx applications,such as SSZ-13,SSZ-24,ZSM-34,ZSM-11 zeolites.The growth mechanism and key synthetic factors of these zeolites were systematically discussed,their physical and chemical properties were revealed through various characterization methods,and the kinetic of the synthesis was studied.The main research contents of each chapter are as follows:1.In recent years,the interzeolite conversion has gradually attracted the attention of researchers,and we aim to use this method to obtain more valuable products.Zeolite SSZ-13 has an excellent performance in petroleum catalytic cracking.We studied the detailed conversion process of two zeolite precursors(including zeolite Beta and zeolite L)into zeolite SSZ-13.Compared with the traditional synthesis of SSZ-13 zeolite,we have developed two excellent starting materials,which greatly shorten the synthesis time and improve the synthesis efficiency.2.SSZ-24,a silicoalumino AFI-type material,proved to be a zeolite with poor synthesis reproducibility and slow crystallization rate.The present study deals with the preparation of SSZ-24 by a seed-assisted approach.SSZ-13 and SSZ-24 zeolites are employed as seeds and the impact of seeds content on the formation of SSZ-24 is studied.Both types of zeolites accelerate the zeolite nucleation,shorten the crystallization time,and lead to the formation of pure and highly crystalline SSZ-24.In addition,SSZ-13 seeds are more efficient in terms of rapid crystallization and crystallinity level.Pure and highly crystalline SSZ-24 is readily obtained even though the amount of SSZ-13 seeds have been decreased to a "catalytic level",i.e.0.3 wt.%.The higher seeding power of SSZ-13 seeds is attributed to the presence of framework Al,which stabilizes structural elements that promote the SSZ-24 nucleation.3.In another study,we have employed zeolite precursors as seeds to synthesize high-purity zeolites ZSM-34,SSZ-13,and ZSM-11.The developed synthetic approach is a more economical and environmentally friendly.Besides shortening the crystallization time,our method allows reaching crystallinity over 90 % and reduction of the amount of template used.This study shows that the newly developed seeding approach combines the advantages of template synthesis and seeded synthesis.The approach is expandable to the synthesis of other zeolites.