Preparation And Catalytic Hydrogenation Of Acid-resistant Nickel-based Catalysts

As a common metal hydrogenation catalyst,nickel-based catalyst has excellent hydrogenation activity.However,under acidic conditions,the loss of active components is serious,which not only causes pollution to the product but also makes the catalyst permanently deactivated,thus restricting the promotion of nickel-based catalyst.For example,in the chlorinated nitrobenzene hydrogenation reaction,the reaction liquid becomes acidic due to the adverse reaction of dechlorination,resulting in the dissolution of nickel-based catalysts（e.g.Raney nickel）,which not only leads to the low conversion rate of reactants,but also leads to the contamination of the reaction system.Therefore,we hope to synthesize a nickel-based catalyst with a carbon（carbon-nitrogen）-encapsulated core-shell structure,so that the catalyst not only prevents the aggregation of highly dispersed metal active components due to the restricted effect of the carbon layer,but also makes the nickel-based catalyst under the protection of the carbon layer can achieve acid resistance to some extent.（1）The phenolic polymer was synthesized by St?ber method and calcined at high temperature under inert atmosphere.By SEM and BET analysis,results show that the structure is a carbon sphere structure with regular morphology and high specific surface area about 490 m²/g,sphere diameter 400-600 nm.In addition,Highly dispersed metal particles can be obtained by introducing metal precursors during the phenolic polymerization process.However,since the metal particles are mainly embedded in the carbon layer,catalysts still do not have acid resistance.（2）A green metal-organic complex（Ni-h₂bdc,bipy）was synthesized by terephthalic acid,4,4-bipyridine and nickel nitrate hydrothermally in N,N-dimethylamide solvent.TG-DTG analyzes the thermal stability of the metal-organic complexes.Through IR,we found terephthalic acid and 4,4-bipyridine form a coordination structure with nickel.Through XRD pattern shows the effect of hydrothermal time on the complex Ni-h₂bdc,bipy.It was found that after 24 hours of hydrothermal,a more stable coordination structure and higher yield were obtained.（3）The effects of the Ni-containing organic complex Ni-h₂bdc,bipy on the final carbon-coated material Ni@CN under different calcination time and calcination temperature were studied by XRD,TEM,XPS,Raman,TPR and other characterization methods.The results show that the calcination temperature below 400℃does not fully carbonize the complex,while the carbon layer above 700℃will crack and the metal particles will partially sinter.TEM results showed that the size distrubution of metal particle sizes were mainly below 10nm.The BET test found that the Ni@CN material obtained by calcinating the precursor at 500℃for 6 h has a large specific surface area（436 m²/g）and the pore size distribution is mainly dominated by micropores.XPS also confirmed that the preparation method of the catalyst can introduce nitrogen in situ.Finally,the synthesis process of core-shell structure is briefly discussed.（4）Hydrogenation of chloronitrobenzene and dimethyl maleate,which can product acid,were used as probes to verify the stability of the catalyst Ni@CN in two acidic environments:inorganic acid（hydrochloric acid）and organic acid（propionic acid）.In the hydrogenation of chloronitrobenzene,the catalyst after hydrochloric acid treatment showed that it had good activity and selectivity when calcined at 500℃for6 h.According to TEM,it was found that the particles were evenly distributed and encapsulated by the carbon layer.In addition,no dechlorination side reaction occurs under the conditions of elevated temperature and hydrogen pressure.And the hydrogenation mechanism of Ni@CN is briefly discussed.In the hydrogenation experiment of dimethyl maleate,the Ni@CN catalyst can react the dimethyl maleate completely in the reaction solution containing propionic acid without Ni loss.The above proves that the catalyst has anti-corrosion ability about organic acid and inorganic acid to some extent.Due to the presence of the Ni component in the catalyst,we can use the magnetism to recycle the catalyst.