Preparation Of Ni-based Nanocatalysts And Their Catalytic Performance For Transfer Hydrogenation Of Halogenated Nitrobenzene

It is of great scientific significance and industrial value to develop a cheap and efficient non-noble metal-based catalyst for the selective hydrogenation of halogenated nitrobenzenes.Non-noble metal Ni-based catalyst is a kind of catalyst which is expected to replace noble metal-based catalysts and is widely used in the catalytic hydrogenation reaction.However,the problems of metal agglomeration at high temperatures,metal leaching during the catalytic reaction and severe dehalogenation greatly limit the application of Ni-based catalysts in practical industry.Therefore,designing highly efficient and stable Ni-based catalysts and modifying strategies to improve their catalytic performance are considered necessary.In this paper,two kinds of Ni-based catalysts were synthesized through the modification strategy of hollow structure support cooperating with adding carbon and nitrogen precursor,and they were applied to catalyze the transfer hydrogenation of halogenated nitrobenzene,both of which achieved good reaction results.The SiO₂ sphere,as a hard template,was coated with Ni（OH）₂ by hydrothermal method.And the hollow precursor H-Ni（OH）₂ was successfully obtained by further etching the SiO₂ template.After mixing melamine with H-Ni（OH）₂ and calcination at high temperature,a hollow structure Ni-based nano-catalyst（H-Ni@NC）with ultra-thin nitrogen-doped carbon coating can be prepared.The unetched Ni₃Si₂O₅（OH）₄ shell in H-Ni（OH）₂ is converted to SiO₂ during calcination,which makes the calcined catalyst maintain good mechanical properties and stability.The Ni（OH）₂ was reduced by carbothermic method to form Ni⁰ in situ,which was coated with an ultra-thin nitrogen-doped carbon layer.It was found that the H-Ni@NC-600,prepared with the same amount of melamine and H-Ni（OH）₂at 600 ^oC,showed the best catalytic performance in the transfer hydrogenation reaction of halogenated nitrobenzene,and it can still maintain good catalytic activity after the cyclic experiment.The performance comparison and structural characterization tests of the catalysts show that H-Ni@NC has the best catalytic performance due to the hollow structure of the catalyst and the protection of the nitrogen-doped carbon layer on Ni⁰.At the same time,the mechanism of transfer hydrogenation of halogenated nitrobenzene was studied.The 3-aminophenol-formaldehyde resin microspheres（AFE）,as a hard template,were coated with Ni（OH）₂ by hydrothermal method to obtain AFE@Ni（OH）₂.After mixing with melamine and depositing with SiO₂ coating,the precursor of the catalyst is obtained.Hollow Ni-based nanocatalysts（Ni-N-C@SiO₂）encapsulated with mesoporous SiO₂ and protected by a nitrogen-doped carbon layer were successfully prepared by calcining the precursor.The introduction of the mesoporous SiO₂ coating and dicyandiamide enabled the catalyst to maintain a large specific surface area(341.56m² g^-1),pore volume(0.26 cm³ g^-1)and high N content（3.62%）after high-temperature calcination.It was found that Ni-N-C@SiO₂-500 catalyst prepared at a mass ratio of2:1 dicyandiamide to AFE@Ni（OH）₂,70μL TEOS and calcination temperature of 500^oC showed the best performance in the transfer hydrogenation of halogenated nitrobenzene.In addition,the catalytic activity of the catalyst did not decrease significantly after several consecutive cycle tests.