The Synthesis And Performance Study Of Magnetic Catalyst Based On Heck Reaction

With the rapid development of science and technology, the research and application of magnetic composite catalyst with nanometer dimensions has been widely used in many aspects recent years. Not only the advantages that the catalyst is more active because of its nanoscale, but also the magnetic characteristics can be seperated by outer-magnetic field easily so that be recycled and reused. Despite the reduction of producing cost, it has a wide range of applications as well as industrial value.In this experiment I selected the composite core-shell structure SiO2@Fe3O4 nanoparticles as a carrier, with Ni (OAc)2 aqueous solution as the source of nickel, CuSO4 aqueous solution as source of copper. Using two types reduction to prepare Ni/SiO2@ Fe3O4 and Cu/SiO2@Fe3O4 heterogeneous catalysts, then using XRD and VSM, TEM analysis means to characterize the structure of the catalyst; Finally choose the Heck coupling reaction reacted between iodine benzene and styrene as model to evaluate catalysts activity, to separate catalysts with the aid of the external magnetic field force and collected catalyst to investigate its repeated use performance by new reactions.The results showed that use the solvent hot method,we have successfully prepared Fe3O4 nanoparticles, the diameter size is about 200 nm, uniform dispersion and have good superparamagnetism; Using sol-gel method to get the uniform core-shell structure carrier SiO2@Fe3O4, with large specific surface area and neat mesoporous channels; The Ni(0) and Cu nanoparticles(0) load on the core - shell carrier was produced form the reduction by sodium borohydride.When I use hydrogen reduction, the 500℃ temperature calcination before reduction is too high to get the zero valence metal, many of the metal elements form various kinds of metal alloy wich have no catalytic properties. However, most of Ni (0) and Cu (0) nanoparticles reduced by Sodium borohydride are loaded on the carrier surface, not the mesoporous channel, did not achieve the desired catalytic effect.The heck reaction of iodine benzene and styrene as model to explore the performance of catalyst showed that the magnetic catalysts Ni/SiO2@Fe3O4 and Cu/SiO2@Fe3O4 all have a certain catalytic activity. The better reaction condition for Ni/SiO2@Fe3O4 catalysts system include:NMP as solvent and K2CO3 as alkali, molecular ratio of iodobenzene:styrene is 1:1.5, molecular ratio of iodine benzene:K2CO3 is 1:1.2. On this condition, iodine benzene conversion can reach to 43.4% as well as selectivity reach to 92.2% while catalyzed by 16.7wt% Ni/SiO2@Fe3O4 and reacted at temperature 150℃ for 24 h. If the reaction time increased to 48h, iodine benzene conversion can reach to 49.3% as well as selectivity 93%. The better reaction condition for catalysts Cu/SiO2@Fe3O4 system is:DMF as solvent, K2CO3 as alkali, molecular ratio of iodobenzene:styrene is 1:1.5, molar ratio of iodine benzene: K2CO3 is 1:1.2; When the Cu proportion of catalyst is 16.7wt%, reacted under the better condition above at 130℃ for 24 h,iodine benzene conversion can reach to 56.9% as well as selectivity 92.7%. If when the reaction time increased to 48 h, iodine benzene conversion rate can reach 63%, selectivity is 93.1%.Two kinds of catalysts are all of good recycling use performance, recovery rate is 85%, can be reused for 3 times.