A Study On Synthesis,Functionalization And Catalysis Of Novel Metallosilicate Zeolites

With the research interests in the field of zeolite materials synthesis and catalytic applications, the contents in this dissertation mainly involve the synthesis and structure analysis of intergrown layered zeolite containing novel topological structure; new preparation methods to hierarchical MWW-type layered zeolites with unit-cell scale and their catalytic applications; construction of chemically functionalized catalytic active center in MWW-type layered titanosilicates; study of catalytic behaviors of composite layered MFI zeolites containing organic structure-directing agents etc.[1] As a kind of important industrial catalyst, the internal structure of zeolite is the fundamental factor determing its performance. Therefore, the synthesis of zeolite with novel topological structure can provide theoretical basis for its potential application. Our study focuses on MWW-type materials, which have strong industrial application background. Utilizing the interaction between inorganic framework and organic structure-directing agents and the feature of layered zeolite growth, we designed a new path for the preparation of zeolite materials with new nanolayers stacking modes for the first time, resulting in a novel zeolite ECNU-5. Comprehensive analysis of X-ray crystallography and electron crystallography reveals that ECNU-5 is a new intergrown structure consisting of two similar but not identical polymorphs. These two kinds of polymorphs are composed of the same MWW nanolayers, but with different stackings due to crytalline dislocation. The relative composition percentage of these two polymorphs was also determined by computer simulation. We further compared the structure of zeolite ECNU-5 and conventional MWW structure and put forward to its potential application fields.[2] Although zeolite crystalline framework provides chemical hydrophobic microenvironment for the active center, its narrow pore entrance cannot meet the demand of diffusion of reactants with large molecular dimensions. The unique flexible structure of the layered zeolite provides more possibilities. Starting from MWW-structured materials, controllable synthesis of hierarchical zeolite material with unit-cell-scale was successfully realized, resulting in the swelling-type MWW layered zeolite Al-ECNU-7P and Sn-ECNU-7P. Comprehensive utilization of various characterization techniques proved that the MWW nanolayers in ECNU-7P were swolled by conventional surfactant (CTAB). This is the first time to obtain the swelling-type MWW zeolite through the hydrothermal synthesis approach. The crystallization process of ECNU-7P, key factor and range were further analyzed. The calcined form ECNU-7 is a hierarchically porous material in unit-cell scale. Finally, ECNU-7 was used for the catalytic conversion of large molecules.[3] Based on the outstanding catalytic properties of titanosilicates in selective oxidations, the organic ligand (piperidine) was introduced into titanium coordination environment by structural rearrangement process to construct a novel catalytic active center. This is the first successful example of six-coordination titanium active site containing organic ligand. The comprehensive utilization of spectrum characterization techniques and theoretical calculations confirm that the novel coordination environment of the active center is really constructed. The catalytic behaviors of Re-Ti-MWW-PI and conventional catalysts in the liquid-phase epoxidation of olefins have been compared, and found that the introduction of piperidine ligand makes the reaction activation energy decrese, thus significantly improves its catalytic performance. On the other hand, the piperidine ligands suppress the acidity of hydroxyl groups, then enhanced the product selectivity in propylene epoxidation. Besides, the novel catalyst exhibits better catalytic stability in alkenes epoxidation.[4] We synthesized a unique surfactant, which could direct the growth of MFI-type layered materials and fix into the zeolite structure firmly. Tandem catalysis has been realized on the multilayered zeolites with organic structure-directing agent occulded within micropores. Two types of base sites were present, that is, the Bronsted and Lewis base sites. The resulting organic-inorganic material can be used as a good acid-base bifunctional catalyst. Supporting the metal palladium nanoparticles on the pure silica layered MFI zeolite containing organic structure-directing agent led to another bifunctional catalyst.