Application Of Graphitic Carbon Nitride In The Selective Oxidation Of Toluene

Toluene is widely used in industry and many high value-added chemicals can be produced through oxidation of toluene.Benzaldehyde,one of the oxidation products,has high value and is mainly produced by chlorination and following hydrolysis which may cause serious pollution.Therefore,using green oxidants such as oxygen,H₂O₂ to oxidize toluene to benzaldehyde not only has theoretical value but also has considerable industrial prospects.However,the C-H bond on the methyl group is difficult to activate.Therefore,it is necessary to find a green and efficient catalyst.Graphitic carbon nitride?g-C₃N₄?is a typical two dimensional layered nano materials.It can be used as metal-free catalyst or catalyst support due to its unique structure.In recent years,some researchers find g-C₃N₄ can activate aromatic molecule and promote related reactions such as hydroxylation of benzene or selective oxidation of aromatic alcohol.Thus this paper aims to study the application of g-C₃N₄ on the selective oxidation of toluene and researches by following ways:?1?g-C₃N₄ was applied to the selective oxidation of toluene in the absence of solvent by using molecular oxygen as an oxygen source.First,the difference in the catalytic performance of g-C₃N₄synthesized from cyanamide and urea was studied and found that the g-C₃N₄ obtained from melamine is more active.Afterwards,the effects of reaction temperature,reaction time,catalyst amount and oxygen pressure on the performance were studied.The performance of the catalyst is further improved by doping with boron.The conversion of toluene is 3.0%and the selectivity of benzaldehyde is 47.8%by using boron-doped BCN₁₀₀00 as catalyst.?2?g-C₃N₄ was used as support in the synthesizing of catalyst and the catalyst was applied to the liquid phase oxidation of toluene by using H₂O₂ as oxidant.It was found that the catalyst in which vanadium oxide was used as active component?V/CN?has good catalytic activity to the selective oxidation of toluene.After that,the influence of loading amount,calcination temperature,solvent,and reaction conditions to the catalyst was studied.When the amount of catalyst is 60 mg and the reaction is carried out at 60°C for 4 h,the conversion of toluene is 30.7%,and the selectivity of benzaldehyde is 56.4%.While,the stability of V/CN is not good enough and could be enhanced when mesoporous g-C₃N₄?mpg-C₃N₄?was used as support.The conversion of toluene is 26.1%and the selectivity to benzaldehyde is 47.6%after three cycles.