Study On The Preparation And Catalytic Performance Of Magnetically Supported Heteropolyacid Catalyst

Heteropolyacid is an effective, stable and environmentally benign catalyst that shows the nicer catalytic capability in chemical reactions in recent years. But heteropolyacid is easy to be dissolved, it is hard to be recycling and reuse. And it has brought considerable difficulties of production disposing and practical applying. The supported heteropolyacid can solve the problem of separation and recovery of catalyst and can overcome the poor stability and the losing of active component of catalyst.Magnetically supported heteropolyacid catalyst was be synthesized combining excellent magnetism of magnetic nanoparticles and supported heteropolyacid. In the magnetic field, magnetically supported heteropolyacid catalyst can be separated simply, which provide a new way of the separation of nano-catalysts.Magnetic Fe₃O₄ nanoparticles with the properties of good dispersancy, high specific surface and strong magnetism was prepared by the coprecipitation method. Using the precursor of TEOS, the surface of magnetic Fe₃O₄ nanoparticles was modified by the method of liquid phase deposition to prepare the magnetic core Fe₃O₄/SiO₂. The chemical property of magnetic core Fe₃O₄/SiO₂ was stable. The resistance to natural weathering of magnetic nanoparticles was improved that satisfied the performance of catalyst.Sub-micron magnetically supported heteropolyacid catalyst (MSHC) was prepared via a sol-gel route. The 12-tungstophosphoric acid and magnetic core Fe₃O₄/SiO₂ were embedded in the silica micropore material. The Fourier Transfer Infra Red (FTIR) results indicate that the 12-tungstophosphoric molecules keep Keggin structure. The MSHC has the excellent activity and the highest esterification ratio in the esterification reaction of n-butyl acetate that approaches the catalytic performance of 12-tungstophosphoric acid. The repeatability and superparamagnetism of the MSHC is fine and the magnetic separation is high efficiency in magnetic field.Magnetically supported heteropolyacid nanoparticles (MSHNs) are successfully obtained via a sol-gel route. They are composed of magnetic Fe₃O₄ nanophase cores, the silica nanocoatings as the anticorrosion layers and the heteropolyacid-silica nanocoatings in which HPA molecules are embedded by sol-gel incorporation technique rather than impregnation method. The particle diameter of MSHNs is 20nm which belong to nano category. 12-tungstophosphoric molecules embedded in silica layers keep Keggin structure after supported. MSHNs used in the esterification reaction of acetic acid and ethanol showed the bad catalytic performance. After the optimization of the reaction condition, the catalytic activity of MSHNs has grate improvement. The result of magnetism testing showed the MSHNs have strong superparamagnetism and the positioning, separation and recycling expediently in magnetic field.