Study On Preparation Of Vanadium-based Catalysts And Their Catalytic Performance For Benzene Hydroxylation

As an important organic chemical product,phenol was widely used in synthetic rubber,fiber,medicine and pesticides.At present,cumene was mainly used in the industrial production of phenol.However,there were still some thorny problems in this process,such as long process flow,serious equipment corrosion,serious pollution of three wastes,low atomic utilization rate,high cost and so on.Therefore,in order to meet the market demand,it was necessary to find a production route of efficient hydroxylation of benzene to phenol instead of cumene,but in order to make a new breakthrough,the core technology was the development of high-efficiency catalyst.Therefore,in view of the existing technical problems,the supported catalyst was prepared with variable valence metal vanadium as the active center,the catalytic activity of the catalyst was further modified,and then the yield of phenol was improved by optimizing reaction conditions.The research contents are as follows:（1）SiO₂ was synthesized by hydrothermal synthesis method as carrier,and VO_x/SiO₂ series catalysts were synthesized by using V₂O₅ as vanadium source.The catalysts were characterized by XRD,SEM,TEM,XPS,NH₃-TPD and other techniques,and the catalytic activity and the structural relationships of catalyst were studied,while optimizing the reaction conditions.Experiments showed that 4%VO_x/SiO₂ was used as catalyst,the catalyst dosage was 0.2 g,4 m L benzene was used as reactant,15 m L acetonitrile was used as solvent,12 m L H₂O₂ was used as oxidant,and the reaction temperature was 70℃for 3h,the conversion rate of benzene was 44.1%,and the phenol selection was 91.3%.（2）In view of the problem of low catalyst selectivity in（1）,SiO₂-Al₂O₃ composite oxide was synthesized by hydrothermal synthesis as a carrier.V₂O₅ was a vanadium source to synthesize VO_x/SiO₂-Al₂O₃ series catalysts,and the catalytic performance of benzene hydroxylation was also investigated.Combined with the results and analysis of characterization techniques such as XRD,SEM,TEM,XPS,NH₃-TPD,and N₂physical adsorption and desorption,the relationship between catalytic activity and catalyst structure was studied.At the same time,the reaction conditions were optimized.The experimental results showed that using 4%VO_x/SiO₂-Al₂O₃ as the catalyst,the catalyst dosage was 0.2 g,4 m L of benzene as the reactant,15 m L of acetonitrile as the solvent,12 m L of H₂O₂ as the oxidant,and the reaction temperature was 70℃for 6h,the conversion rate of benzene was 48.1%,the selectivity of phenol was 99.6%.（3）In view of the relatively low conversion rate of the catalyst in（2）,the conversion rate of benzene was increased in order to keep the selectivity of phenol basically unchanged.Through the hydrothermal synthesis method,Ga₂O₃/SiO₂-Al₂O₃composite oxide was synthesized as a carrier,and then the VO_x-Ga₂O₃/SiO₂-Al₂O₃series catalysts were synthesized.The catalysts were characterized by XRD,SEM,TEM,XPS,NH₃-TPD and other techniques and the relationship between catalytic activity and catalyst structure was studied.The reaction conditions were optimized at the same time.The experimental results showed that using 4%VO_x-4%Ga₂O₃/SiO₂-Al₂O₃ as the catalyst,the catalyst dosage was 0.2 g,4 m L of benzene as the reactant,15 m L of acetonitrile as the solvent,12 m L of H₂O₂ as the oxidant,and the reaction temperature was 70℃for 5 h,the conversion of benzene was 74.3%and the selectivity of phenol was 98.1%.