Preparation,Characterization And Catalytic Performance Of Three-dimensional Doped Graphene Supported Palladium Catalysts

The selective oxidation of benzyl alcohol is an important chemical reaction.The product benzaldehyde is a permissible synthetic fragrance for foods as specified in GB 2076-2011.It is also an important intermediate in the production of fine chemicals and flavorring additives Metal catalysts are commonly used for the oxidation of benzyl alcohol to benzaldehyde,among which platinum noble metal catalysts have the best catalytic effect.Metal palladium has high catalytic activity and wide range of palladium sources,and its application in selective oxidation of benzyl alcohol has attracted much attention.The active phase in metal catalysts is nano-sized metal particles,but nano-sized palladium particles are easy to agglomerate and lose,which limits their application.One of the effective solutions is to immobilize palladium metal particles on suitable carriers.Graphene has many excellent properties,such as good thermal conductivity,high mechanical strength and large specific surface area.It is considered to be an ideal carrier for loading metal nanoparticles.However,the perfect zero band gap structure of graphene greatly reduces the modifiable space of graphene,which limits its application as a metal catalyst carrier.Heteroatom doping can open the band gap of graphene,significantly change the electronic distribution and local bonding environment on the surface of graphene.Doped graphene will produce more defects and active sites,which is conducive to improving the stability of metal particles.In addition to changing the composition of catalyst support,it is also an effective way to enhance the catalytic activity of graphene-based catalysts by building a reasonable porous structure to increase the specific surface area of catalysts.Three-dimensional graphene retains the advantages of two-dimensional graphene,and its abundant pore structure can further increase the specific surface area,provide more space for the dispersion of metal nanoparticles,and prevent the agglomeration of metal nanoparticles to a certain extent.Therefore,three-dimensional doped graphene can be used as a good metal catalyst carrierIn this paper,we use graphene oxide prepared by Hummer as precursor,doped graphene with different dopants,prepared three-dimensional porous catalyst materials by hydrothermal method,and investigated its catalytic performance in selective oxidation of benzyl alcohol The main research contents are as follows1.Preparation and characterization of three-dimensional nitrogen-doped graphene supported Pd composite catalyst and its catalytic performance in selective oxidation of benzyl alcoholThree-dimensional nitrogen-doped graphene supported palladium catalyst(3DPd/NRGO)was synthesized by hydrothermal method from flake graphite and graphene oxide prepared by Hummer method and NMP as nitrogen source.The optimum reaction conditions for selective oxidation of benzyl alcohol were explored.The optimum catalysts were screened by exploring different mass ratios of NMP/GO and different palladium loadings.The results showed that the catalyst had the best catalytic effect when the mass ratio of NMP/GO was 1.5:1 and the palladium loading was 8%under the reaction conditions of 90 ? and 3 h.The catalysts were further characterized by Raman,XRD,TEM,FT-IR,XPS,BET and SEM.The results showed that nitrogen was successfully incorporated into the graphene material,and the doped graphene material had more defects than the undoped graphene material.At the same time,the three-dimensional structure provided the catalyst with abundant pore structure and large specific surface area.The combination of these two points successfully reduced the particle size of Pd nanoparticles(3.2 nm),and improved the stability of the catalyst.The catalyst activity did not decrease significantly after 6 cycles of recycling2.Preparation,characterization and catalytic performance of Pd composite catalyst supported on nitrogen and sulfur co-doped graphene for selective oxidation of benzyl alcoholWith ammonia thiocyanate as nitrogen source and sulfur source,Pd/NSRGO co-doped graphene catalysts were prepared by a simple,green and environmentally friendly method,keeping the load of palladium unchanged.Selective oxidation of benzyl alcohol was used as a model reaction to screen out the best catalyst with the best nitrogen and sulfur content.When the mass ratio of NH4SCN/GO is 6/5,the catalytic activity of the catalyst is the best,which is higher than that of single nitrogen doping.Its excellent performance is attributed to the co-doping of nitrogen and sulfur.There is a strong interaction between heteroatoms and metal nanoparticles,which can disperse and stabilize nanoparticles.The results showed that both nitrogen and sulfur were successfully incorporated into graphene.TEM results showed that Pd nanoparticles were evenly dispersed on the surface of graphene sheets co-doped with nitrogen and sulfur.The average particle size of Pd nanoparticles(2.9 nm)was smaller than that of N-doped graphene sheets(3.2 nm).