Synthesis,Characterization And Application Of Yolk-shell Structured Zeolite Composites

Yolk-shell nanostructures（YSNs）are a class of composite nanomaterials containing movable cores,cavities,and porous shell.Owing to their unique structural features,such as hierarchical pores,hollow cavities,and functionable cores and shells,YSNs have attracted wide applications in catalysis,energy storage and biomedicine.Microporous zeolites are widely used in catalysis due to their unique features,incuding high specific surface area,strong acidity and shape selectivity.However,theapplication of microporous zeolites in some complex organic reactions are restricted,which is caused by their surface properties and narrow pore openings.Periodic mesoporous organosilica（PMOs）is a class of organic-inorganic hybrid materials,which has been widely used in the fields of drug mitigation,multiphase catalysis and chemical sensors.The preparation of yolk-shell structure with molecular sieve as the core and mesoporous organosilica as the shell can expand the applications of molecular sieve materials,such as one-pot Deacetalization-Knoevenagel cascade reactions,Styrene liquid phase epoxidation,etc.In Chapter Two,we prepared acid-base bicentric yolk-shell structured HY@NH₂-PMO composites by using organosilicon directed growth-induced corrosion method,in which Y molecular sieve as the core and silica as the hard template.The products were characterzed using SEM,TEM,XRD,FTIR,N₂adsorption and other techniques.The results demonstrate that the composite materials exhibit a hybrid of microporous and mesoporous structure,which can facilitate the diffusion rates of both reactants and products.The HY@NH₂-PMO-1 catalyst achieved 100%conversion of benzaldehyde dimethyl acetal and 98%yield of the target product benzylidenemalononitrile in 3.5 h in the catalytic one-pot cascade Deacetalization-Knoevenagel reaction with good recyclability and structural stability.The basic sites of the catalyst can be tuned by adjusting the amount of 3-aminopropyltriethoxysilane used during the growth-induced corrosion method.,However,this can also block some of the microporous pores of HY molecular sieve,leading to a decrease in the activity of the catalyst.In Chapter Three,new yolk-shell structured TS-1@Ph-PMO hierarchical pore composites can be synthesized by using organosilane 1,4-di（triethoxymethylsilyl）benzene growth-induced corrosion method,in which the TS-1 molecular sieve is used as the core and silica is used as the hard template.The structures were characterized by using SEM,TEM,UV-vis,N₂adsorption and other analytical methods.TS-1@Ph-PMO-2 has a large specific surface area（870.4 m²/g）and a high pore volume（0.739 cm³/g）.The mesoporous organosilica Ph-PMO backbone of phenyl can improve the hydrophobicity of the composites and can effectively regulate the diffusion of reactants and product molecules in the reaction of liquid-phase oxidation of styrene with tert-butyl hydroperoxide,which in turn improves the styrene conversion and increases the ethylene oxide selectivity.