Design Of G-C₃N₄-based Heterogeneous Catalysts For Catalytic Oxidation

With the increasingly serious environmental pollution and energy exhaustion,green chemical industry has become a hotspot in the field of chemical engineering.Based on the special two-dimensional（2D）crystal structure and suitable band gap,a series of carbon nitride-based heterogeneous catalysts were designed and applied to epoxidation of alkenes and selective oxidation of alcohols.The reaction is efficient and environmentally friendly.And the heterogeneous catalysts can be recovered by simple centrifugation for steady reuse.（1）Au/g-C₃N₄compositecatalystwaspreparedbythe deposition-precipitation method.TEM and UV-vis confirm that the gold nanoparticles（particle size of 10-13 nm）were uniformly dispersed on the surface of g-C₃N₄.The special layered structure of g-C₃N₄ is beneficial to the reaction mass transfer,and the g-C₃N₄ material is rich in pyridinium nitrogen and amino groups,which provide anchored sites for capturing nano gold particles.In addition,the basic position of g-C₃N₄ can activate hydrogen peroxide,and the Au/g-C₃N₄ composite catalyst exhibits excellent performance in epoxidation of olefins with hydrogen peroxide as an oxidant.The catalyst can be facilely recovered by simple centrifugation,and be reused for several times without significant loss of activity and selectivity.（2）Two-dimension g-C₃N₄ nanosheets were prepared by high temperature oxidation etching.The prepared nanosheets have a large specific surface area and good dispersibility in water.More importantly,it enhances the band gap of carbon nitride,improves the electron transport ability,and extends the life of the charge carrier.As a result,it exhibits superior photocatalytic performance in selective oxidation of alcohols to carbonyl compound in water under air atmosphere and ambient conditions.Quantitative yields of carbonyl compounds,such as aldehydes and ketones,are obtained over the carbon nitride nanosheets.The reaction is environmentally friendly and fully meets the requirements of green chemistry.（3）Using AuCl₄ and PdCl₂ as precursors,Au-Pd alloy nanoparticles were supported on the surface ofγ-Al₂O₃ by coprecipitation-reduction method.The catalytic activity was controlled by adjusting the precursor ratio to adjust the Pd/Au molar ratio in the Au-Pd alloy nanoparticles.Studies have shown that the higher the dispersion of Pd active sites in the alloy,the higher the catalytic performance.With Au-Pd_1.2@γ-Al₂O₃ as catalyst,water as solvent and air（1 atm）as oxygen source,alcohol（fatty alcohol,aromatic alcohol,polyhydric alcohol,etc.）can be quantitatively converted into corresponding Aldehyde or ketone.The TOF value is as high as 22.3 h^-1.After the reaction is completed,the catalyst can be easily recovered and effectively reused by centrifugation.