Study On Catalytic Oxidation Of Benzene To Phenol Over Vanadium Based Catalyst With Molecular O₂

Phenol is an important organic chemical intermediates,mainly used in phenolic resin,pharmaceutical intermediates,pesticides,spices,synthetic dyes and other fine chemicals.The technology for the preparation of phenol is cumene method,which has many steps,harsh processing conditions and the overall low efficiency.Furthermore,the production cost was fluctuated by the price of the byproducts of acetone..Therefore,study on the green synthesis of phenol is becoming a hotspot.The direct oxidation of benzene to phenol with molecular oxygen has the advantages,it not only byproduct is water,and is environmentally benign,less reaction steps,high atom utilization and low cost.These are consistent with the basic requirements of green chemistry.So the direct oxidation of benzene to phenol with molecular oxygen has attracted widespread attention and become a hot research topic.The contents of this thesis are as follows:In order to study the mechanism of direct oxidation of benzene to phenolwith moledular oxygen,a series of V_xO_y@C catalysts were prepared with varied biomass?sucrose,glucose,fructose,ascorbic acid?as carbon source and ammonium metavanadate as vanadium source.The catalysts were characterized by IR,XRD,TG,SEM,XPS,N2-adsorption,and particle size distributions.Furthermore,the catalytic performances were investigated.The study on the mechanism of the catalyst showed that active oxygen speices was generated by ascorbic acid and molecular oxygen with the help of V species in the catalyst.The benzene ring was attacked by the active oxygen speciese to form phenol.The catalytic activity of the catalysts mainly depended on the active component of vanadium species while the selectivity of phenol was influenced by the adsorption of phenol on the catalyst and the overoxidation of phenol.Phosphorus was introduced to the V_xO_y@C catalyst to prepare the VOPO4@C catalyst whose catalytic performance was investigated.A series of VOPO4@C catalysts was obtained with sucrose,ammonium metavanadate,and different phosphate as raw material by the hydrothermal method.The reaction condition for preaparation of the catalyst was optimized.The obtained VOPO4@C catalyst was characterized by IR,XRD,TG,SEM.The catalytic performance on the direction oxidation of benzene to phenol with molecular oxygen was investigated.The reaction conditions including the dosage of catalyst,the amount of the additive,reaction temperature,reaction time,and solvent were optimized.It was found that the yield of phenol was 10.9% under the optimal reaction condition of 1.0 mL benzene.3.0 mL acetonitrile,25 mg catalyst,0.8 g ascorbic acid,3.0 MPa oxygen,80 ?for 4 h.V_xO_y/?-Al₂O₃ catalyst was prepared with neutral alumina precursor carrier,with ammonium metavanadate and oxalate complexes as vanadium source.The catalyst was characterized by IR,XRD,and XPS.The reaction conditions including the dosage of catalyst,the amount of the additive,reaction temperature,reaction time,and solvent were optimized.It was found that the yield of phenol was 11.1% under the optimal reaction condition of 1.0 mL benzene.3.0 mL acetonitrile,50 mg catalyst,0.8 g ascorbic acid,3.0 MPa oxygen,80 ?for 4 h.In addition,the adsorption of benzene and phenol on the catalyst was investigated.It was found that the adsorption of benzene on the V_xO_y/?-Al₂O₃ catalsyt was the presudo second order adsorption while the adsorption of phenol was the presudo first order adsorption.