Study On The Catalyst For Liquid Phase Oxidation Of Toluene To Benzaldehyde

By selective oxidation,oxygen-containing groups are introduced into aromatic hydrocarbons to obtain petrochemical products with high added value,which is of great significance to the technological progress of petrochemical industry.However,the pyrolysis and oxidation of C-H bonds requires high temperature,high pressure and high efficiency catalysts,which remains a huge challenge.Toluene is a simple aromatic compound,which can be oxidized to benzyl alcohol,benzaldehyde and benzyl benzoate.Among them,benzaldehyde is widely used in food,pharmaceutical,spices and pesticides industries.However,benzaldehyde is easily oxidized to benzoic acid.The traditional production route of benzaldehyde is chlorinated hydrolysis of toluene.However,chloride ions are inevitably left in this process,which is not easy to remove,and a large amount of wastewater is produced,resulting in environmental pollution and equipment corrosion.To make matters worse,benzaldehyde prepared by this route can not be used to synthesize high-quality compounds such as medicines or perfumes.Therefore,it has better economic and social benefits to develop catalysts for high-efficiency oxidation of toluene to benzaldehyde and to develop new technologies for green synthesis of Benzaldehyde from toluene.In this paper,nanorod structure V_3.6Mo_2.4O₁₆6 catalyst was prepared by sol-gel-high temperature solid-state reaction method.Ultra-thin N-doped nanosheet porous graphite phase carbonitride material was prepared by ultrasonic assisted hydrothermal treatment.M-N-mpg-C₃N₄ catalyst was prepared by doping transition metal modification.The catalysts were characterized by XRD,XPS,SEM and TEM.The structure-activity relationship of the catalyst and its catalytic performance was investigated.The process conditions of selective oxidation of toluene to benzaldehyde on the above catalysts were also investigated.The effects of reaction time,pressure,reaction solvent and the amount of oxidant on the catalytic performance were investigated.The results show that the catalysts with different vanadium molybdenum ratios can be prepared by sol-gel high temperature solid-state reaction.When the ratio of vanadium to molybdenum is 10:7,pure V_3.6Mo_2.4O₁₆6 compounds can be obtained.The vanadium-molybdenum ratio has a significant effect on the structure of V_3.6Mo_2.4O₁₆,and the calcination temperature affects the morphology of the catalyst.When the calcination temperature is 540℃and the vanadium molybdenum mass ratio is 10:7,there is no MoO₃ on the surface of V_3.6Mo_2.4O₁₆,and the nanorods with regular shape are obtained.The diameter is about 200 nm,the length is up to several tens of micrometers,and the surface is smooth.The activity of V_3.6Mo_2.4O₁₆6 catalyst was as follows:the conversion of toluene was 39.8%,and the selectivity of benzaldehyde was 70.1%.Compared with other catalysts,nanorod V_3.6Mo_2.4O₁₆showed high activity while showing High selectivity to benzaldehyde.In addition,the catalyst was recycled and reused 5 times without any significant change in catalytic activity and selectivity.Ultra-thin N-doped nanosheet porous graphite phase carbonitride was prepared by ultrasonic assisted hydrothermal method for liquid phase oxidation of toluene.It was found that the catalyst exhibited high selectivity to benzaldehyde.Compared with the mesoporous g-C₃N₄ catalyst prepared by bulk and non-ultrasonic assisted hydrothermal treatment,the ultra-thin N-doped nanosheet porous graphite phase carbon nitride exhibits better catalytic performance.The catalyst has no solvent catalyzed reaction at a certain oxygen pressure and temperature,the toluene conversion rate is up to 2.8%,and the benzaldehyde selectivity is up to 99.9%.In order to improve the conversion of toluene to the catalyst,the paper selected doping modified ultrafine N-doped nanosheet porous graphite phase carbon nitride by using Co,Fe,Cu,V and Mo.The results show that V-g-C₃N₄ catalyst prepared by V-doping modification greatly improves the conversion of toluene,without affecting the selectivity to benzaldehyde.The conversion of toluene increased from 2.8%to 5.1%.