Study On Ni-Based Catalysts For Hydrogenation Of Phenol To Cyclohexanol

Cyclohexanol is a kind of widely used industrial raw material and it is the solvent for the preparation of fiber,rubber and paint as well as the chemical intermediate for the preparation of nylon-66.Currently,there are two synthetic routes for the industrial preparation of cyclohexanol:the oxidation of cyclohexane and the hydrogenation of phenol.The former method requires relative high reaction condition and will results in high energy consumption,large pollution.Besides,there are many by-products in this route and the yield of cyclohexanol is low.By contrast,the cyclohexanol obtained by hydrogenation of phenol has good quality,moreover,the reaction condition is mild and the yield of cyclohexanol is high.Given that,the later one has broad industrial application prospects.The traditional phenol hydrogenation catalyst is mainly based on noble metal Pd.Although the catalytic performance is promising,it is difficult to use in large-scale industrial production because of the lack of Pd source and high cost.Many scholars have found that Ni-based catalysts have good catalytic performance in the catalytic hydrogenation of phenol to cyclohexanol and considering the abundant source and low price of Ni,Ni-based catalysts have good industrial value.In recent years,the design of highly efficient,green,and inexpensive Ni-based catalytic system has become a research hotspot in the field of phenol catalytic hydrogenation reactions.In order to design a high efficient Ni-based catalytic system for the hydrogenation of phenol to cyclohexanol,this paper first prepared the Ni/C catalyst by using KBH₄ reduction method,combined adsorption method and hydrogen reduction method,respectively.Under the same reaction conditions,The conversion of phenol with these three catalysts was 96.3%,93.4%and 83.28%,the selectivity of cyclohexanol was 99.6%,98.8%and 99.3%,respectively.The catalyst prepared by KBH₄ reduction method possessed the best catalytic performance.Specific surface area and pore structure tests?BET?,X-ray diffraction?XRD?,X-ray photoelectron spectroscopy?XPS?,and adsorption-desorption?TPD?were used to analyze the structure and surface properties of the catalyst.The catalyst nanoparticles prepared by KBH₄ reduction method have the most uniform distribution and less agglomeration,which is more favorable for the catalytic hydrogenation reaction.The results of the characterization and catalytic hydrogenation of the catalyst were found to be consistent.The characterization results are consistent with the experiment results.In order to further improve the phenol hydrogenation performance of Ni-based catalyst.On the basis of single-metal Ni/C catalysts,the effects of different promoters on the performance of the catalysts were studied.The addition of Fe can significantly increase the activity and selectivity of Ni-based catalysts for the hydrogenation of phenols and show the best synergistic catalytic effect.The effect of different atomic ratio of NiFe on the catalytic performance of phenol hydrogenation to cyclohexanol was studied.It was found that when the reaction temperature was 120°C,reaction pressure was 3.5 MPa,iso-propanol was used as solvent and the NiFe atomic ratio was 2:1,the conversion of phenol can reach to 99.9%,and the selectivity can reach to99.9%.Due to the addition of Fe atoms?NiFe atomic ratio of 2:1?,the electrons between the metals were transferred,Ni atoms became electron-rich state and unsaturated catalytic activity centers,which is more favorable to the adsorption of reaction species.At the same time,the catalyst structure and surface characteristics were analyzed and it was found that the catalyst has large specific surface area,the metal nanoparticles are more unformly distributed,besides there is a strong interaction force between the carrier and the metal nanoparticles,and the metal nanoparticle do not easily agglomerate,Therefore,enhance the catalytic performance of the Ni/Fe bimetallic catalyst.On this basis,the performance of the as-synthesized catalyst remained stable after 5 times catalytic reaction.In summary,with the addition of metal auxiliaries,due to the synergy between metals,electron transfer occurs between the metal auxiliaries and the active components,and some of the electrons in the active components become unsaturated centers which is favorable for the adsorption of hydrogen species.This effectively improves the catalytic performance of the catalyst.The NiFe bimetallic catalyst prepared by the KBH₄ reduction has large specific surface area,uniform distribution of nanoparticles and no agglomeration,and is efficiently applied to the hydrogenation of phenol to cyclohexanol?the conversion of phenol can be reach to 99.9%and the selectivity of cyclohexanol can reach to 99.9%?.At the same time,the catalyst has excellent stability and rich reserves of metallic Fe and Ni,so it has high industrial application value.