The Synthesis And Performance Study Of Magnetic Core/Shell Structured Aluminum Oxide Catalyst

Magnetic nano-catalyst is a new type of catalytic materials. It not only showshigh catalytic performance, but also can be effective separation and recyclingunder the external magnetic field due to its magnetism, which brings to hugeeconomic benefits.In this paper, the core/shell structured γ-AlOOH@Fe₃O₄and γ-Al₂O₃@Fe₃O₄magnetic microspheres have been prepared successfully by the hydrilysis ofaluminium isopropoxide （AIP）. The superparamagnetic Fe₃O₄microsphereswhich were synthesized by the improved solvothermal, were used as themagnetic cores. Then, Pd/γ-AlOOH@Fe₃O₄and Pd/γ-Al₂O₃@Fe₃O₄catalystshave been prepared with γ-AlOOH@Fe₃O₄and γ-Al₂O₃@Fe₃O₄magneticmicrospheres as the supporters. The obtained magnetic microspheressupporters and catalysts were characterized by X-ray powder diffraction（XRD）、nitrogen adsorption-desorption and vibrating sample magnetometer（VSM）. The size and morphology of supporters and catalysts were alsoexamined using transmission electron microscopy （TEM） and scanningelectron microscopy （SEM）. The catalytic performance of catalysts had been studied with iodobenzene and butyl acrylate as the Heck reaction model.The results indicated, in the preparation process of Fe₃O₄microspheres, whenthe reaction time was1h, the mol rate of PVP/FeCl₃·6H₂O was3/40and theamount of NaAc was30g, the obtained Fe₃O₄microspheres had regularspherical structure, uniform size （about200nm）, and at room temperature, themaximum saturation magnetization of77.0emu/g.When AIP concentration was0.016mol/L and hydrolysis time of AIP was1h,the continuous γ-AlOOH shell with the average thickness of5nm was formedon the surfaces of Fe₃O₄microspheres. And the thickness of γ-AlOOH shellcould be controlled by layer-and-layer coating process. The formationmechanism of γ-AlOOH shell could be interpreted as a―chemisorptions-hydrolysis‖process. The γ-Al₂O₃@Fe₃O₄magneticmicrospheres could be obtained by calcining γ-AlOOH@Fe₃O₄microspheresunder500℃. The γ-Al₂O₃@Fe₃O₄magnetic microspheres remained thecore/shell structure.When Pd/γ-AlOOH@Fe₃O₄and Pd/γ-Al₂O₃@Fe₃O₄（3.0wt%Pd） catalystswere used to catalyze the reaction of iodobenzene and butyl acrylate, theconversion rate of iodobenzene were all100%under reaction temperature of120℃and reaction time of1.5h. The3.0wt%Pd/γ-AlOOH@Fe₃O₄and3.0wt%Pd/γ-Al₂O₃@Fe₃O₄catalysts had high saturation magnetization,56.6emu/g and43.0emu/g respectively, which could be seperated easily fromliquid phase under the external magnetic field. The3.0wt%Pd/γ-Al₂O₃@Fe₃O₄ catalysts have been reused for6times, and the catalytic activity was stillwithout a bit lower.