Synthesis, Characterization And Catalytic Properties Of MFI Zeolites Composites

Titanium Silicalite-1(TS-1) with MFI topological structure was firstly synthesized by Enichem (Italy) in1983. TS-1exhibits excellent catalytic and oxidative performance using H2O2as oxidant under mild reaction conditions, and thus attracts more attention by many researchers. However, there is a big problem in industrial process for the conventional TS-1zeolite, where nanosized zeolites make the filtration difficult and large zeolite particles severely suffer diffusion limitations. To assemble nanosized zeolites into large aggregates by physical or chemical forces could not only solve the filtration problem but also reduce the diffusion limitations.Based on the traditionally hydrothermal synthetic methods, we have put forward to two post-synthetic methods to prepare TS-1aggregates using different silica species as binder. The contents of the master's thesis in details are as follows:One method is to use colloidal mesoporous silica (CMS) with positive electrical charges and very small size (20nm) as binder. In general, TS-1is of negative charge in the alkaline synthetic condition. Electrostatic attraction will play a major role when mixing the TS-1zeolite and colloidal mesporous silica. In this part, the effect of several important factors such as the zeolite particle size, the molar SiO2ratio in zeolite and CMS and post crystallization on the physicochemical properties of TS-1samples have been investigated systematically. Under optimized experimental conditions, the final product has a comparable catalytic performance with the conventional TS-1zeolite and could be more easily separated and recovered using conventional filtration.The other method is to assemble TS-1zeolite using the bridged organosilanes. The bridged organosilane are a class of organic-inorganic hybrid materials, and are widely used in the synthesis of molecular sieves and periodic mesoporous organosilicas. In this part we discuss the hydrolysis and condensation of bridged organosilanes under acidic and alkaline experimental conditions respectively to assemble the TS-1nanopartilces. Under alkaline conditions, the parameters including the type of the silane reagent, alkalinity changes and other factors were investigated. The bridged organosilanes show different hydro lytic rates under the acidic system and alkaline condition. We expect periodic mesoporous materials (PMO) will be wrapped up molecular sieve particle surface under acidic conditions, resulting in a hierarchical zeolite materials, where the acidity, the co-solvents, surfactants and silylation reagent species, as well as other factors such as reaction temperature, reaction time and particle size, were investigated.The third part is to add mesopogen (CTATOS) to the synthetic mixture of TS-1or Silicalite-1at different hydrothermal conditions and then further crystallize in order to achieve hierarchical microporous-mesoporous materials. Besides ultrasonic treatment or not and orher parameters, there is still a lot to be discussed.