Preparation And Catalytic Performance Of Ag Nanoparticles Encapsulated By Zeolite Molecular Sieves

The active sites of silver nanoparticles are easy to be exposed,which have certain adsorption and activation ability for oxygen molecules,and show excellent catalytic activity in CO oxidation and olefin oxidation.However,silver nanoparticles tend to agglomerate at high temperature,resulting in instability of catalytic performance.Zeolites are widely used in industrial catalytic reactions and separation of small gas molecules due to their ordered microporous structures,adjustable acidity and redox sites.Compared with other nano porous materials,zeolites show better hydrothermal stability and chemical stability.Metal nanoparticles can be confined in the cages and pores of zeolites to prevent the aggregation.Therefore,zeolite can be used as ideal supports for encapsulation of metal nanoparticles.In addition,the synergistic effect of metal nanoparticles and porous framework with active sites can further improve catalytic activity of the composite catalysts.In this thesis,silver nanoparticles with good adsorption and activation ability for oxygen molecules were encapsulated in aluminosilicate molecular sieves(ZSM-5)to study their catalytic performance for CO oxidation and styrene oxidation.The main results are summarized as follow.1.CO is one of the most widely distributed and abundant air pollutants,accounting for one third of the air pollution.The elimination of CO has high practical value and research significance in real life.Catalytic oxidation of CO by chemical method has become an important research topic in the field of environmental protection.In this thesis,Ag@ZSM-5 was successfully synthesized by one-pot method using the complex of silver ion with diethylenetriamine as structure directing agents.Ag@ZSM-5 was characterized by X-ray diffraction,nitrogen adsorption desorption,scanning electron microscopy and X-ray fluorescence,which showed Ag@ZSM-5 with different Si/Al ratios had good crystallinity,single morphology,and the mass fraction of Ag is 5%-7%.Furthermore,the catalytic performance of CO oxidation was investigated using Ag@ZSM-5 with different Si/Al ratios.Under certain conditions,with the increase of Si/Al ratio,the catalytic activity of Ag@ZSM-5 increased gradually.2.The oxidation of styrene has high research value,whose products are organic synthesis intermediates for wide applications.Among them,benzaldehyde and epoxyphenylethane attract widely attention.As a valuable organic product,benzaldehyde is widely used in pharmacy,dyestuff,perfume and agriculture.Many traditional synthesis methods are used to produce benzaldehyde,such as indirect oxidation of toluene,oxidation of toluene,hydrogenation of benzoic acid and hydrolysis of benzyl chloride.In this thesis,based on one-pot method for synthesizing Ag@ZSM-5,Ag@S-1 was successfully synthesized via adding the complex of silver ion with diethylenetriamine or ethylenediamine into the precursor of S-1.The oxidation reactions of styrene were investigated with Ag@S-1.With the prolongation of reaction time,the conversion of styrene gradually increased to 87%at 90 ~oC.Meanwhile,the selectivity of benzaldehyde increased to 57%,and the selectivity of epoxy phenylethane decreased to 18%.