Magnetic Immobilized Iron-copper Alloy Nanomaterial With Core-shell Structure And Its Application In Catalytic Transfer Hydrogenation Of Nitroarenes

Aromatic amines especially haloanilines are extremely important valuable intermediates for fabricating various products such as medicine,pesticides,surfactant and other chemical products.Accordingly,the preparation of aromatic amines from reduction of nitroarenes has attracted much attention in recent years.Compared to the traditional methods of metal/acid reduction and catalytic hydrogenation,catalytic transfer hydrogenation is an environmentally benign protocol for the manufacture of nitroarenes with the advantage of easy handling and mild reaction condition.In this process,hydrazine hydrate is widely used with the merits of its high hydrogen content and high safety.Our work focused on a new kind of core-shell catalyst Fe3O4@SiO2-NH2-FeCu with ultrafine FeCu NPs encapsulated in the supporter.Using hydrazine hydrate as hydrogen source,the catalyst was applied to reduce nitroarenes.The study results and important conclusions are summarized as follows:Firstly,we synthesized Fe3O4 nanospheres by solvothermal method and cladded porous silica as a supporter to immobilize active sites.Then using reduction method by NaBH4,the ultrafine FeCu NPs were encapsulated in the micro tunnel through the confinement effect to obtain core-shell catalyst Fe3O4@SiO2-NH2-FeCu.The catalyst was used to explore catalytic activity to determine the best metal ratio with p-nitrophenol as the model substrate and hydrazine hydrate as the hydrogen source.The catalytic selectivity was investigated using parachloronitrobenzene as the model substrate,which demonstrated that the dechlorination did not occur.The XPS study showed that the good result was contributed from the electron-enrichment of Fe from Cu.Meanwhile,a kinetics analysis indicated that the apparent active energy(Ea)toward parachloronitrobenzene was 48.1 kJ mol-1,which was a relatively low value.It was worth mentioning that during the reduction process,there is no dechlorination or by products generated even when reducing other nitroarenes.The catayst could be recycled at least 10 times without any change in catalytic performance.As a consequence,the excellent stability of the catalyst could be ascribed to the two facts:(1)The active sites are encapsulated in the silica spheres and dispersed well by the amino groups,which can restrain the aggregation phenomenon during the reaction.(2)The active sites are magnetically attracted to the magnetic core,which helps to immobilize the active component to avoid wastage.