Studies On The Preparation And Catalytic Properties Of Magnetic Core-shell Catalytic Materials

The preparation and catalytic properties of magnetic mesoporous Fe3O4@SiO2@mSiO2-Fe,Fe3O4@SiO2@mSiO2-Pd and Fe3O4@SiO2@mSiO2-Ag catalysts with core-shell structures have been studied by using various physical and chemical methods such as X-ray diffraction(XRD),Fourier transform infrared spectroscopy(FT-IR),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy(XPS)and vibrating sample magnetometer(VSM)combined with micro-reactor tests.The results have provided the important reference information for research and development of magnetically separable mesoporous catalysts.The main results are as follows:1.The core-shell catalytic materials Fe3O4@SiO2@mSiO2-Fe with magnetic Fe3O4 as the core and amorphous SiO2 and the Fe-doped mesoporous silica as the double shells were prepared.The catalytic properties and recycling properties of this kind of catalytic materials with different composition and structure for selective oxidation of styrene to benzaldehyde were studied.The results have shown that the isolated Fe3+species in the framework of shell of Fe3O4@SiO2@mSiO2-Fe catalyst are the main catalytically active species.The optimum Fe/Si molar ratio in the catalyst shell is 0.10,and the appropriate reaction temperature is 60℃.The catalyst can be separated easily by magnetic field,and the catalysts have excellent recycling performance.2.The magnetic mesoporous Fe3O4@SiO2@mSiO2-Pd catalysts with core-shell were prepared,and the catalytic properties and recycling performance of the catalysts for hydrogenation of naphthalene were studied.It has been shown that Pd nanoparticles were highly dispersed in the shell of mespporous SiO2,and Fe3O4@SiO2@mSiO2-Pd catalysts have excellent catalytic activity for naphthalene hydrogenation.The catalysts were easier to separate from reaction system in magnetic field.After 10 cycles,the naphthalene conversion and the selectivity of hydrogenation products were remained almost unchanged.3.The magnetic mesoporous Fe3O4@SiO2@mSiO2-Ag catalysts with core-shell structure were prepared,and the catalytic properties and recycling performance of the catalysts for reduction of 4-nitrophenol(4-NP)to 4-aminophenol(4-AP)were studied.The results have shown that the Ag nanoparticles were highly dispersed on the surface of mSiO2 through the anchoring of Ag+species.For the fresh Fe3O4@SiO2@mSiO2-Ag catalyst,the reduction of 4-NP to AP can be completed in 12 minutes,and the reaction rate constant k was 5.3×10-3 s-1.After 10 cycles,the reaction time needed for the complete conversion of 4-NP to 4-AP was only increased from 12 min to 16 min,showing excellent recycling performance.