Preparation Of GO-based Pickering Emulsion And Its Catalytic Application In Hydroxylation Of Benzene To Phenol

Phenol is an important organic chemical raw material,and its industrial production mainly uses the three-step isopropyl benzene method,but this method has the problems of long synthesis route,high energy consumption and low yield of phenol.With hydrogen peroxide?H₂O₂?as the oxidant,the hydroxylation of benzene to phenol was characterized by fewer steps,mild reaction conditions and green process.However,in this one-step reaction,the problems of low product selectivity and low effective utilization of H₂O₂ still exist,and acetonitrile and other solvents need to be added to the reaction system to carry out the reaction effectively.Therefore,the design and preparation of a multifunctional and efficient catalyst system is the key to solve the above problems.In this paper,a Pickering emulsion system with interfacial catalytic properties was prepared by using the"amphipathic"characteristics of graphene oxide?GO?materials,and according to the GO material surface modification,explore the use of the GO-based materials stabled Pickering emulsion system.Without organic solvent and stirring,implement the hydroxylation of benzene reaction.By Raman,XRD,FTIR and XPS,Uv-vis characterization methods,analysis the non-metallic materials and the load of metal oxide GO-based materials surface structure change on the reactivity influence of hydroxylation of benzene.It mainly explores the following contents:?1?By screening the preparation conditions of Pickering emulsion such as ultrasonic time,ultrasonic power,oil/water volume ratio and GO concentration,it can be known that when the ultrasonic time is 10 min,the ultrasonic power is between 450 W and 540 W,the oil/water volume ratio is 0.6,a relatively stable GO-based Pickering emulsion can be formed.When the concentration of GO solution was 8?12 mg/m L,the prepared Pickering emulsion was the most stable.The volume fraction of the emulsion was 100%,and remained unchanged within 72 h at room temperature.?2?GO and reduced state GO?rGO?were prepared by Hummers method,chemical reduction method and electrochemical method.The Pickering emulsion formed by GO was the most stable,without oil and water separation during the reaction process.The selectivity of phenol was greater than 99%,but the yield of phenol was only 2.1%.The stability of Pickering emulsion formed by rGO was lower than GO,but the yield of phenol could reach4.6%.The reason why the catalytic activity of rGO was higher than GO may be that the increase of rGO surface defect sites after reduction,promoting the adsorption and activation of benzene and the desorption of the phenol,while the surface structure of GO could not provide a more efficient catalytic active site for the benzene hydroxylation reaction.The hydrophilic and high catalytic activity sites of the material play a synergistic role in the hydroxylation of benzene catalyzed by GO-based Pickering emulsion.?3?In order to improve the catalytic activity of GO-based materials,non-metallic doped GO-based materials?NGO,BGO and SGO?and GO-based materials loaded with metal oxides?Fe₂O₃/rGO and VO_x/rGO?were prepared by hydrothermal and roasting methods.At 50 o C,in NGO,SGO and BGO stable Pickering emulsion catalytic system,the conversion rate of benzene was lower than that of rGO,slightly higher than that of GO,and the selectivity of phenol was greater than 99%.In the VO_x/rGO?20 wt%?stable Pickering emulsion catalytic system,the conversion rate of benzene reached 9.7%,slightly lower than that the hydroxylation of benzene system with acetonitrile as the solvent under the same conditions.At room temperature,the Pickering emulsion system with Fe₂O₃/rGO stable iron precursor loading capacity of 5 wt%had the highest catalytic activity,and the conversion rate of benzene was up to 9.2%and the selectivity was 91.1%,which was higher than the hydroxylation of benzene reaction system with acetonitrile as the solvent under the same conditions.It shows that in the GO-based Pickering emulsion catalytic system,the effective contact between the reactants and the emulsion interface can be realized by building a"micro-reactor",so as to improve the catalytic reaction activity.