Study On The Preparation Of Supported Nickel-based Catalyst And Its Hydrogenation Performance

Graphite oxide（GO）was synthesized by Hummers method from flake graphite.Nitrogen-doped reduced graphene oxide（N-r GO）support was prepared by hydrothermal method using urea as nitrogen source,and then Ni/N-r GO catalyst was prepared by impregnation method.The prepared catalysts were characterized and analyzed by N₂ adsorption-desorption,XRD,SEM,H₂-TPR and other test methods.Taking the selective hydrogenation of phenol to cyclohexanone as the reaction system.Through the single factor experiment and orthogonal experiment to investigate the active component load,urea addition,H₂ reduction temperature,the reaction temperature,reaction pressure and reaction time on the phenol conversion and the effects of cyclohexanone selectivity,then the optimal preparation and reaction conditions of catalyst were determined;The effects of storage time,reuse times and different supports on the performance of the catalyst were also investigated.In addition,the mechanism of phenol hydrogenation catalyzed by Ni/N-r GO catalyst was also investigated.Finally,Ni/N-r GO catalyst was modified by adding auxiliaries,and the catalyst with good modification effect was analyzed and characterized.The experimental results show that the Ni/N-r GO catalyst prepared under the condition of20% nickel loading,1:30 urea/GO mass ratio and 450 ℃ reduction temperature has a large specific surface area and suitable pore structure.The dispersion of active metal nickel is relatively uniform,but the local agglomeration is obvious.Doping appropriate nitrogen atoms can effectively reduce the reduction temperature of the catalyst;Under the optimum conditions of reaction temperature of 150℃,reaction pressure of 0.4 MPa,reaction time of 2.0 h,catalyst /phenol mass ratio of 0.35,the catalytic effect of Ni/N-r GO catalyst was the best,the conversion of phenol was 91.93%,the selectivity of cyclohexanone was 61.75%,and the storage time and catalyst recycle experiments found that Ni/N-r GO catalyst has good stability;Ni/N-r GO catalytic phenol hydrogenation mechanism shows that there is a good π-π conjugate adsorption between grapheme and phenol,and the proper doping nitrogen atoms can effectively reduce the acidic properties of oxygen-containing groups on the surface of graphite.OH — N or OH —π interaction may be formed after adsorption of N-r GO and phenol,which is beneficial to the rapid desorption of cyclohexanone from graphite surface and effectively improves the selectivity of cyclohexanone.The Ni/N-r GO catalyst was modified by adding auxiliaries such as Ce,Cu,Fe and Na,and used in the hydrogenation of phenol.The results showed that the modification effect of additive Ce was the best.When the molar ratio of cerium to nickel was 0.2,the conversion of Ni-Ce/N-r GO catalytic phenol was 95.21% and the selectivity of cyclohexanone was 72.57%.The characterization results show that: After the addition of auxiliaries Ce the catalyst showed a porous structure,the specific surface area and pore size of the catalyst increased significantly,the large particles agglomerated on the surface of the catalyst basically disappeared,the metal nickel dispersion was more uniform,and the catalytic effect was better.