Study On Modification Of Pd/C₃N₄ Catalyst For Light-Promoted Oxidation Of Benzyl Alcohol To Benzaldehyde

Benzaldehyde is widely used in food,pharmaceutical,perfume and other industries.In recent years,benzyl alcohol is often used as a raw material to oxidize benzaldehyde by thermal catalytic means,but this reaction usually requires the use of organic solvents or more severe conditions to obtain high conversion and high selectivity.Therefore,it is particularly important to explore and develop a catalyst that can efficiently oxidize benzyl alcohol to benzaldehyde under relatively mild conditions.The graphite phase carbon nitride（g-C₃N₄）has a band gap suitable for ultraviolet-visible light absorption（2.7 e V）,which can convert incident photons into localized heat,which is considered to be a broad application in photothermal drive catalysis.Prospective photocatalytic materials are expected to use this photothermal agent to drive thermocatalytic reactions that usually require an external heat source or high pressure.However,the photo-excited electrons and holes of g-C₃N₄are prone to rapid recombination and low visible light utilization rate,which leads to poor photocatalytic performance for the oxidation of aromatic alcohols to aromatic aldehydes.Therefore,it is necessary to be modified.In this paper,the carrier g-C₃N₄is modified by hydrothermal method,and Pd nanoparticles are loaded on the surface of the modified carrier to catalyze the oxidation of benzyl alcohol in a solvent-free system.The specific research content and conclusions are as follows:（1）Use direct hydrothermal method to synthesize hydroxylated carbon nitride（OH-C₃N₄）carrier and load Pd nanoparticles.Characterization by elemental analysis,XPS,TEM,PL,etc.proved that hydrothermal treatment can increase the hydroxyl groups on the surface of g-C₃N₄,increase the specific surface area,but basically do not change its original structure,and make the supported palladium nanoparticles more dispersed,the particle size is reduced to 4.53 nm.The content of Pd⁰in the catalyst has increased by nearly 10%.The 1%Pd/OH-C₃N₄-180-8 catalyst prepared by hydrothermal treatment at 180℃for 8 h has the best performance in the oxidation of benzyl alcohol.The optimal reaction conditions for this reaction are 100℃,8 h,and the optimal amount of catalyst is 100 mg.Compared with 1%Pd/C₃N₄,1%Pd/OH-C₃N₄-180-8 catalyst increased the conversion rate of benzyl alcohol by22.13%,the yield increased by 19.41%,and the selectivity was 93.85%.When light is added,the conversion rate and yield of the catalyst before and after the hydroxylation modification to benzyl alcohol are increased,and the conversion rate of1%Pd/OH-C₃N₄-180-8 catalyst is higher than that of 1%Pd/C₃N₄to benzyl alcohol.The selectivity and yield of benzaldehyde were increased by 32.99%,7.5%and29.52%,respectively.（2）Oxygen-doped carbon nitride（O-CN）carrier was prepared by H₂O₂hydrothermal method.Characterization by elemental analysis,XPS,PL,etc.proved that H₂O₂hydrothermal treatment can not only increase the crystallinity of CN,but also doping with O to increase the content of O.the particle size of Pd in1%Pd/3O-CN is about 4.24 nm,and the content of Pd⁰increases from 62.23%to86.96%.The experimental results show that when the H₂O₂concentration is 3%,the reaction conditions are 100℃,8 h,and the catalyst dosage is 75 mg,1%Pd/3O-CN has the best performance in the reaction.The conversion rate reached 63.60%,the selectivity reached 91.71%,and the yield rate reached 58.33%,which was 31.68%higher than the 1%Pd/CN conversion rate,the yield increased by 28.23%.When light was added,the conversion of benzyl alcohol,selectivity and yield of1%Pd/3O-CN were increased to 86.34%,85.71%and 74%,respectively.Compared with 1%Pd/3O-CN,the conversion and yield of benzyl alcohol were increased by42.34%and 35.52%.