Preparation Of Submicrospheres Fe₃O₄@PDA-Pd NPs And Its Application In Catalytic Hydrogenation,Dehydrogenation And Heck Reaction

Metal-supported catalysts supported on superparamagnetic carriers have attracted the attention of chemists because of their good dispersion,simple separation and reusability.Fe₃O₄ particles are the most common magnetic carriers because of their easy availability of raw materials,simple preparation and high magnetic properties.The particle size of superparamagnetic ferric oxide prepared by chemical method is usually small,and it is easy to be oxidized in air,resulting in the decline of magnetic properties.The particle size of large size ferrous oxide microspheres is superparamagnetic and high magnetic.It is not only good dispersion,simple separation,but also stable in air environment.In this paper,a preparation method of nano-palladium?Pd NPs?metal catalyst supported on sub-microspheres Fe₃O₄@PDA has been developed.The catalyst has good performance in selective hydrogenation reduction of halogenated aromatic nitro compounds and chalcone derivatives,dehydrogenation of aromatic methanol and nitrogen heterocycles,and Heck reation of iodoaromatic hydrocarbons and acrylates.This dissertation include the following five parts:?1?Some general examples of the preparation methods of Fe₃O₄ magnetic micro/nanoparticles,their advantages and disadvantages,the modified composite of Fe₃O₄ particles and its application in catalytic reaction were reviewed.?2?In the preparation of Fe₃O₄@PDA-Pd NPs,a layer of polydopamine was coated on the surface of Fe₃O₄ particles by the self-polymerization of dopamine to form Fe₃O₄@PDA-core-shell sub-microspheres.The microspheres were then protonated to be charged positively.The PdCl₄^2-was adsorbed and dispersed on the surface by positive and negative charge attraction.The nano-palladium loaded on the core-shell sub-microspheres with large particle size,superparamagnetic and high magnetic Fe₃O₄@PDA was further prepared by reduction.The composite is stable in air environment and has high dispersion of palladium on the surface of microspheres.The thickness of the polydopamine layer of the complex Fe₃O₄@PDA-Pd NPs can be controlled by the dosage of dopamine and reaction temperature,and the palladium content can be controlled by the thickness of polydopamine layer and the dosage of palladium?II?.The Fe₃O₄@PDA-Pd NPs were analyzed and characterized by XRD,IR,TGA,SEM,EDS,TEM,ICP-AES and magnetic properties test.?3?Fe₃O₄@PDA-Pd NPs catalyzed the hydrogenation of halogenated aromatic nitro compounds and chalcone derivatives under atmospheric pressure.The reaction temperature and solvent were optimized.The results showed that the prepared Fe₃O₄@PDA-Pd NPs could efficiently reduce halogenated aromatic nitro compounds to halogenated aromatic amines,with high selectivity and few side reactions of dehalogenation and C-N coupling.Dihydrochalcone derivatives were obtained by efficient reduction of chalcone derivatives without any side reaction of carbonyl reduction.Fe₃O₄@PDA-Pd NPs catalyst is easy to recover and can be reused.?4?When Fe₃O₄@PDA-Pd NPs catalyzed the dehydrogenation reaction of aromatic methanol and nitrogen heterocycles,the reaction temperature,time and oxidant conditions were optimized.The results show that aromatic formaldehyde with medium yield and high selectivity can be prepared by oxidative dehydrogenation of aromatic methanol catalyzed by Fe₃O₄@PDA-Pd NPs in air.It can also effectively dehydrogenate nitrogen heterocycles,especially fused ring.?5?When Fe₃O₄@PDA-Pd NPs catalyzed Heck reaction of iodoaromatic compounds and acrylates,the reaction temperature,time,amount of catalyst,solvent and base were optimized.The results showed that Fe₃O₄@PDA-Pd NPs could catalyze Heck reaction of iodoaromatic compounds and acrylates under air environment.The reaction conditions were mild and the yield was high.Substitutes are well tolerated in this reaction.In a word,the Fe₃O₄@PDA-Pd NPs composite prepared in this dissertation is a sub-microsphere with large size and core-shell structure.Palladium nanoparticles are highly dispersed on the surface of the composite.It has the characteristics of superparamagnetism,high magnetism and air stability.It has high activity and selectivity in various catalytic reactions.It can be simply separated by magnet and reused.