Synthesis Of Magnetic Catalysts And The Study Of Their Catalytic Performance For 4-Nitrophenol Reduction

Due to their high catalytic activities and good magnetic separation properties,magnetic nano-catalytic materials have shown superior merits in photocatalysis,organic synthesis catalysis and wastewater treatment compared with traditional catalysts.Generally,the magnetic materials are synthesized using Fe₃O₄,a particle easy to prepare and strong in magnetism,as the core.Through surface coating,a uniformly dispersed magnetic compound nanomaterial with large specific surface area is resulted.Preparation of arylamines from aromatic nitro-compounds have played a significant role in many areas including fine chemical engineering,fuel and medicines,andthe catalytic reduction method has been commonly used.Among those methods,preparation of p-aminophenol from4-Nitrophenol reduction has been one of the most representative reaction.In this paper,we mainly demonstrated the preparation of three supported catalysts and the study on their activities to catalyze 4-Nitrophenol reduction.The main researches are as follows:The Fe₃O₄ nanoparticles was synthesized in the method of co-precipitation.And the TEOS hydrolyzed on the as-prepared Fe₃O₄ nanoparticles' surface to form a layer of SiO₂.Then,the ?-mercaptopropyltrimethoxysilane was used to modify the outer of the Fe₃O₄@SiO₂ to obtain the magnetic particles containing sulfydryl group.The nano-Ag was loaded as activate state by impregnation method.The NaBH4 was used to reduce the Fe₃O₄@SiO₂-SH/Ag nanoparticles with catalyst activities.And the product was characterized by FI-IR,AAS.The catalytic performance of the catalysts was also tested employing the reduction of 4-nitrophenol to 4-aminophenol with NaBH4 added.The result shows that the catalytic property of which silver nitrate is added to form Ag nanoparticles is better than Tollens' reagent.The dynamic constants of the two for the first run are0.0371s-1 and 0.0181 s-1,repectively.But both recycle rates are not very high.The crylic acid was grafted on the oligomer--Methylene-Bis-Acrylamide which was packaged on the surface of Fe₃O₄ nano-particles.Then the nano-Ag was loaded on the organic supporters.FI-IR,AAS,TGA,TEM and XPS were performed to character the product.The result shows that the high polymer with carboxyl group can effectively prevent the nano-Ag from agglomerating.And the material have high catalytic activitytoward reduction of 4-np.The transform ratio is 100% in 23 seconds and the TOF is3.78min-1.the rate constant is 0.0244s-1 in the fourth run,which is shorter than most catalysts' time for the first test.Moreover,the catalyst can be separated quickly by magnet.The catalyst still have activities after the fifth run.The magnetic Fe₃O₄ is used as the core to synthesize the mesoporous silicon dioxide wrapped magnetical nanoparticles.Then,the product was impregnated in silver nitrate and ruthenium trichloride solutions respectively.Finally,the loaded Ag and Ru were got by reduction of NaBH4 to form Fe₃O₄@meso-SiO₂/Ag and Fe₃O₄@meso-SiO₂/Ru nanoparticles.The product were charactered by FI-IR,AAS,TGA,TEM and XPS.The catalyst activity and the recycle rate are tested with NaBH4 added.the result shows that the former has relatively high catalyst activity and the recycle rate.The catalyst still works after recycle use for 8 times.The dynamic constant is k=0.0208 s-1.The Fe₃O₄@meso-SiO₂/Ag also has good stability.It can keep stable under basic solution for42 days,While,the catalyst activity of Fe₃O₄@meso-SiO₂/Ru is not so good.The dynamic constant of it is k=0.055 s-1.The T-1 raney nickel was successfully synthesized.The comparison of properties of catalytic hydrogenation reduction toward 4-np between Fe₃O₄@meso-SiO₂/Ru and raney nickel has been conducted.The experiments were performed under two systems which are water and anhydrous methanol.The result shows that the reaction can take place in water and methanol rather than in anhydrous methanol.The activity test reflects that on the same conditions,the catalyst activity of Fe₃O₄@meso-SiO₂/Ru is 8 times higher than raney nickel.The data demonstrated that the Fe₃O₄@meso-SiO₂/Ru can be well applied in industry.