A Study On Synthesis And Characterization Of Novel Metallosilicate Zeolites

Hierarchical and large-pore zeolites are synthesized in this study, with the purpose to relieve the structural constrains that large-size molecules encountered in the small-and medium-pore zeolites. Post-synthesis methods are employed to synthesize mesopore-containing Ti-MOR zeolite and interlayer-expanded PLS-4zeolite. The catalytic properties of mesoporous Ti-MOR zeolite in the liquid-phase selective oxidation reactions and the adsorption abilities of interlayer-expanded PLS-4zeolites over H2O, n-hexane and benzene are invetigated. Moreover, the structural stabilization of large-or extra-large-pore germanosilicates through isomorphous substitution of Si for Ge is another important part of this thesis. The structural changes during the stabilization process are carefully investigated. Germanosilicates are found to be active in the Baeyer-Villiger oxidation reaction for the first time.Ti-containing hierarchical porous MOR zeolite is synthesized in the first part of this thesis by a combination of alkaline treatment for mesopore formation and gas-solid reaction for insertion of Ti atoms. Industrial MOR zeolite with a relatively low Si/Al ratio is adopted as the starting material. As a result, an acid treatment is needed to remove some of the Al atoms, which favoring the following alkaline treatment. Another acid treatment is also carried out to remove the remaining Al atoms in the framework before the Ti insertion process. Thus, the Ti-Meso-MOR zeolite prepared with an acid-alkaline-acid treatment and gas-solid Ti insertion process show higher mesopore volume and external surface area than conventional Ti-MOR zeolite. As the mesopores favor the interconnection of the one-dimensional12-member ring (MR) channels, Ti-Meso-MOR shows higher activities in the hydroxylation of toluene and ammoximation of cyclohexanone.In the second part of this thesis, layered zeolite PLS-4is interlayer silylated to form an interlayer-expanded zeolite PLS-4-sil. Temperature, concentration of acid aqueous solution and the amount of silane have effect on the structure of the obtained interlayer expanded zeolite. Appropriate condition is performed to prepare a structural ordered PLS-4-sil zeolite. Controlled calcination treatments are carried out on the as-synthesized PLS-4-sil zeolite, forming a series of zeolites with different pore opening and hydrophobicity/hydrophilicity. And these zeolites show different adsorption abilities of H2O, n-hexane and benzene.A general method is disclosed to increase the stability of germanosilicates in the third part of this thesis. Germanosilicates are subjected to the acid treatment at extremely high temperature, in which silicon atoms form the framework or additionally added isomorphously replace the Ge atoms. As a result, the Si/Ge ratios are increased and the structures are stabilized without changing the topology. IM-12zeolite with the topology of UTL is adopted as the example to investigate the structural changes after the acid treatment.97%of the Ge atoms are removed during the acid treatment. However, the double-4-member rings as well as the crystalline structure are intact after the acid treatment.The structural changes of as-synthesized UTL zeolite and calcined UTL zeolite are studied in the fourth part of this thesis when they are subjected with acid treatment at high temperature. Both of the zeolites show a structural deconstruction and structural repairing phenomena. The same structure as the parent is obtained in the case of UTL zeolite, which is not in the case of calcined UTL zeolite. Many characterization methods are performed to study the reason for the differences of structural changes. Several zeolites with different interlayer space and hydrophilicity are obtained through controlling the acid.treatment time over calcined UTL zeolite. Moreover, these zeolites show variable adsorption and catalytic properties.In the last part of this thesis, the catalytic properties of germanosilicates including IM-12, IM-20, ITQ-17and ITQ-24in the Baeyer-Villiger oxidation reaction of ketones (mainly2-adamantaone and cyclohexanone) are studied. All of the four germanosilicates are active in the Baeyer-Villiger oxidation reaction with BEC zeolite having the highest activity. BEC zeolite also possesses the highest initial reaction rate because of the3-dimentional12MR pores and nano-sized crystals. Pyridine adsorbed IR and in-situ IR technology are carried out to study the mechanism of this Baeyer-Villiger oxidation reaction catalyzed by germanosilicates. It is disclosed that the ketones are firstly active by the Ge atoms with Lewis acidity and then oxidized to corresponding lactones with the help of H2O2. The structures of the four germanosilicates keep intact after they are used in the liquid-phase oxidation reaction.