Catalytic Oxidation Of Toluene To Benzaldehyde By Hydrogen Peroxide

Benzaldehyde is an important chemical raw materials and intermediates,which is widely used in perfumes,dyes and plasticizers.Traditionally,benzaldehyde is produced by chlorinating of–CH₃ functionality of toluene and followed by saponifying,which may discharge waste with a low benzaldehyde yield.Moreover,the products in this method are limited to utilization in food industries and pharmaceuticals due to the chlorinated contaminants.Therefore,it is of great significance to seek an efficient and clean process for the synthesis of benzaldehyde.In this paper,a series of catalysts with high activity and selectivity for the selective oxidation of toluene to benzaldehyde were prepared by controlled synthesis.The relation between the structure and properties of the catalyst was discussed,which provided basic data and technologies for the selective oxidation of toluene to benzaldehdye.The novel highly efficient Mo O₃-Mo V₂O₈ and Mo O₃-Fe₂?Mo O₄?₃-Mo V₂O₈catalyst was prepared by sol-gel method.And Mo O₃-Mo V₂O₈@Fe₃O₄ catalyst was prepared by introducing Fe₃O₄ magnetic core.Considering the special spatial structure and electron distribution characteristics of the graphite-type carbon nitride?g-C₃N₄?,Mo V₂O₈/g-C₃N₄ catalyst was assembled.The activity of above catalysts was evaluated by using hydrogen peroxide as the oxidant for catalytic oxidation of toluene to benzaldehyde.The structure of the catalyst was analyzed by XPS,SEM,TG-DSC,XRD and TPR,and the structure-activity relationship of catalyst was revealed,which provided important basic data for the design and assembly of the selective oxidation reaction catalyst.The results showed that when the catalyst composition is V/Mo ratio of 1/1,and the Mo O₃-Mo V₂O₈ catalyst precursor was calcined at 550°C,the toluene conversion of 36.0%and 53.2%benzaldehyde selectivity were achieved as the reaction was performed at 80°C for 8 h.In order to improve the selectivity to benzaldehyde,we modified above synthesized Mo O₃-Mo V₂O₈ catalyst by doping transitional metal?Co?Cr?Ce?La and Fe?and made the final decision of iron as the best additives.When V/Mo/Fe raitio was 6/7/1,the toluene conversion of 40.3%and 84.5%selectivity to benzaldehyde were obtained.XRD results showed that the existence of Fe₂?Mo O₄?₃.XPS analysis indicated that the introduction of Fe increased the electron cloud density of the molybdenum in the catalyst,thus improved the selectivity to benzaldehyde.To solve the problem of separation of solid catalyst after reaction,the Mo O₃-Mo V₂O₈ catalyst was self-assembled on the Fe₃O₄ surface,and the Mo O₃-Mo V₂O₈@Fe₃O₄ magnetic catalyst with core-shell structure was prepared.The results showed that the vanadium-molybdenum mixed oxides dispersed on the surface of Fe₃O₄ can be self-assembled at 550°C as Mo O₃-Mo V₂O₈ crystal phase.The toluene conversion and selectivity to benzaldehyde were 36.6%and 79.8%respectively.After the reaction,the catalyst could be quickly collected by adding an external magnetic field.Based on the special spatial structure of graphite-type carbon nitride?g-C₃N₄?and the excellent catalytic performance in catalysis,the Mo V₂O₈ was self-assembled on the surface of g-C₃N₄ by high temperature solid-state reaction.The effects of preparation process on the structure and performance of Mo V₂O₈/g-C₃N₄ catalyst were investigated.The results showed that toluene conversion and benzaldehyde selectivity were 43.5%and 72%,respectively,and the yield of benzaldehyde was31.3%.