Preparation Of Spinel Ferrites And Investigation Of Their Catalytic Performances On Selective Oxidation And Suzuki Coupling Reactions

Metal oxides, especially magnetic nanocrystals of complex oxides such as spinelferrites become more important in recent years due to both their unique properties andbroad range of applications in diverse areas such as magnetic recording and separation,ferrofluid, magnetic resonance imaging (MRI), biomedicine, catalysts, gas sensors,high quality ceramics and superparamagnetic materials. A great advantage of usingmagnetic ferrite nanocrystals as catalysts in liquid-phase reactions is that the catalystsare not only thermally and chemically stable in the solution medium, but also easy tobe recovered because of their magnetic property. As a matter of fact, these catalystscan be separated from the reaction medium by simply placing a magnetic field on thesurface of the flask. Additionally，spinel ferrites can be used as magnetic supports forheterogenization of homogeneous catalysts..It is well known that the properties and applications of ferrites commonly dependon their shapes, sizes and structures. Over the past decades, ferrite nano-materialswith various morphologies including spheres, wires, cubes, triangles, hollows andoctahedrons have been successfully synthesized and this has greatly extendedapplications of the ferrite materials. From both economy and environment aspects,using of green oxidants and solvents is desirable in selective oxidation reactions. Thishas impelled many researchers to investigate truly “green” technologies. This thesisaims at development of ferrite catalysts with high effectiveness and following studieshave been carried out.(1) Magnetic ferrite Mg1-xCuxFe2O4(x=0,0.1,0.3,0.5,0.7,0.9,1.0)nanocrystalline complex oxides were prepared by sol-gel auto-combustion method.Their catalytic performances were evaluated in oxidation of styrene in water usinghydrogen peroxide (30%) as oxidant. The results have shown that the samples areefficient catalysts for the oxidation of styrene to benzaldehyde. Especially, whenMg0.5Cu0.5Fe2O4was used as catalyst,21.8%of styrene conversion and83.9%ofselectivity for benzaldehyde were obtained at80oC for9h reaction. Preparationmethods and morphologies also have great influences on catalytic performance of the catalyst. A s a result, hollow spheres of Mg0.5Cu0.5Fe2O4has shown greatly improvedcatalytic activity than solid ones. When this hollow sample was used as catalyst,18.2%of styrene conversion and49.4%of selectivity for benzaldehyde can be obtainedafter11h reaction under atmospheric pressure of O2using TBHP as initiator.(2) Five magnetic core-shell type Fe3O4@chitosan-Schiff base Co(II), Cu(II) andMn(II) complexes were prepared in a simple way and well characterized by Fouriertransform infrared spectrophotometry (FT-IR), X-ray photoelectron spectroscopy(XPS), X-ray diffractometry (XRD), Transmission electron microscopy (TEM),Dynamic light scattering (DLS) and thermogravimetry (TG). Their abilities tocatalyze oxidation of cyclohexene with molecular oxygen in the absence of anysolvents or reducing agents were investigated. It has been revealed that theas-prepared samples have high catalytic activities for heterogeneously aerobicoxidation of cyclohexene and2-cyclohexene-1-one is the main product in all cases.Especially, the catalyst can be magnetically separated easily for reuse and no obviousloss of activity was observed when reused in five consecutive runs.(3) Cu-Pd ferrites with high specific surface areas were prepared by usingmesoporous SBA-15and MCM-41molecular sieve as templates and wellcharacterized by Fourier transform infrared spectrophotometry (FT-IR), X-raydiffractometry (XRD), transmission electron microscopy (TEM) and N2adsorption–desorption. Catalytic performances of the as-prepared catalysts on Suzukicoupling reaction were investigated. The results have shown that the catalysts havehigh catalytic activities and recyclabilities. As a result, when the sampleCu0.99Pd0.01Fe2O4prepared by using MCM-41as a template was used as catalyst, ashigh as2.5×103TON can be obtained and no obvious decrease in the activity wasobserved after ten consecutive runs.