The Construction Of Metal Nanoparticles Confined In The Hierarchical Hollow SiO₂ Catalyst And Its Selective Catalysis

In order to solve the disadvantages of easy agglomeration of metal nanoparticles（MNPs）and poor recyclability of supported catalysts in the catalytic process,as a result,this dissertation constructs a novel confined catalytic system,obtaining supported catalysts with high stability,catalytic activity and good recyclability,in which the metal active center can be introduced into the inner SiO₂,while outer SiO₂ can act as the protect shell for MNPs,preventing the aggregation and leaching in the catalytic process.Therefore,the confined catalyst not only exhibits the excellent performance of supported metal catalysts;but also enhances catalytic efficiency and cycle life because the catalytic reaction take places in the very narrow space based on the active center confined in nanospaces of inner SiO₂ and outer SiO₂.The catalytic system of hierarchical hollow SiO₂,in this dissertation,is prepared via several steps:（1）cationic polystyrene spheres was used as templates,tetraethoxysilane（TEOS）and allyltriethoxy silane were coated on the surface of templates by sol-gel hydrolysis because of electrostatic attraction,forming PS/SiO₂ core-shell structure.（2）metal cations(Ag⁺,Au³⁺)are subjected to deposit on the surface of SiO₂ through impregnation method due to its negatively charged nature,and then the cationic monomer（DMC）and styrene were co-polymerized so as to surround the surface of PS/SiO₂,preparing PS/SiO₂-M+/PS spheres;（3）the second SiO₂ can be prepared by using the same technique of（1）;（4）the hierarchical hollow SiO₂ confined catalyst SiO₂/Ag/SiO₂ was successfully synthesized by calcination and the reduction of NaBH4.This method not only can effectively realize the quantitative loading of the metal nanoparticles,but also can realize the control of the confined space by using the thickness of the second layers of styrene templates.Compared with the traditional supported catalysts,the catalyst（SiO₂/Ag/Si O₂）not only exhibited higher catalytic activity and stability for the hydrogenation of nitrobenzene,but also holds a good selective catalysis which the hydrogenation of p-nitrophenol not happen until the most of nitrobenzene（78.4%）was hydrogenated in the mixture solution of nitrobenzene and p-nitrophenol.For this,we further prepared gold nanoparticles confined catalysts,and systematically investigated the effect of various factors including catalytic substrate concentration,reaction temperature and amount of catalyst on the catalytic selectivity and its the structure-activity relationship.It was found that the higher the concentration of the catalytic substrate can lead to a higher selectivity because the stronger hydrogen bond.Also the lower the amount of catalyst is benefit for the enhanced of selectivity.The implementation of the research work of this dissertation not only enriches the types of confined catalysts,but also sets up a facile method for the preparation of metal nanoparticles confined in the hierarchical hollow silica,making it more potential in hydrogenation of for the aromatic nitro compounds to aniline.