Preparation Of Pd Catalysts Supported On Carbon Nitride And Ceria And Application In Selective Oxidative Of Benzyl Alcohol

Benzaldehyde is an important raw chemical compound,which is extensively applied for the production of dyestuff,pigment,pharmacy,and other fine chemicals.Currently,Benzaldehyde is manufactured through the toluene chlorination/hydrolysis process,however suffering drawbacks of complicated operation procedures and chlorine contamination.On the other hand,the method of direct oxidation of toluene also suffers difficulty in activating toluene and therefore the resultant yield of benzaldehyde is very low.By comparison,selective oxidative of benzyl alcohol in the presence of O₂ provides a more sustainable approach for the synthesis of benzaldehyde,which thus has been attracted in the field of catalysis recently.With regard to the selective oxidation reaction,supported noble metal catalysts represented by Pd possess higher catalytic activity than the non-noble metal catalyst.Wherein,the catalytic activity of the noble metal catalysts is largely related to the particle size,dispersion,chemical valance,and the property of the catalyst supports.Recently,as a new carbon-based material,graphitic carbon nitride（g-C₃N₄）has been extensively used in various research fields including photocatalysis,thermal catalysis,fuel cells,etc.g-C₃N₄ contains rich nitrogen-containing species that can be used to load and disperse transition metals.In this dissertation,a series of supported Pd catalysts have been prepared using g-C₃N₄ as a support,and then evaluated in the selective oxidation of benzyl alcohol.In order to further improve the catalytic activity of the supported Pd catalysts,Pd was supported in CeO₂ and CN-wrapped CeO₂（CN/CeO₂）materials and examined in the selective oxidation of benzyl alcohol.The dissertation includes the three following sections.First,exfoliated g-C₃N₄ was prepared through a second calcination method using dicyanodiamide（DCDA）as a precursor,and subsequently,Pd/eg-C₃N₄ catalysts were prepared.Several characterization methods including N₂ adsorption-desorption,XRD,TEM,TG,XPS,FT-IR,UV-vis,were used to characterize the physicochemical properties of the catalysts.The result indicates that exfoliation could improve the surface area and pore volume.Pd species existed in the form of Pd⁰ on the surface of eg-C₃N₄,and interacted with the nitrogen of eg-C₃N₄.With 3Pd/eg-C₃N₄-500 as a catalyst,the maximum conversion of benzyl alcohol and selectivity to benzaldehyde were 70%and 99%,respectively,under 90℃ of reaction temperature and at 4 h of reaction time.Second,CeO₂ materials were prepared using Ce（NO₃）3·6H₂O as a precursor and then utilized as supports to prepare Pd/CeO₂.The effect of the preparation temperatures of CeO₂ on the contents of Ce³⁺and Pd⁰ in Pd/CeO₂ was been investigated by several characterization methods.In the selective oxidation of benzyl alcohol,3Pd/CeO₂-550 demonstrated superior catalytic activity to 3Pd/CeO₂ catalysts prepared with other temperatures,which might be due to its higher Ce³⁺and PdO contents.Under 90℃ of reaction temperature and at 4 h of reaction time,the maximum conversion of benzyl alcohol and selectivity to benzaldehyde were 75%and 99%,respectively.Third,since CeO₂ possesses lattice oxygen while CN can disperse noble metal,CN-wrapped CeO₂（CN/CeO₂）materials were further synthesized.The impact of the incorporating amount of CN on the contents of Ce³⁺and Pd⁰ in Pd/CN/CeO₂ was analyzed.In the solvent-free selective oxidation of benzyl alcohol,Pd/CN/CeO₂ showed higher catalytic activity than either Pd/eg-C₃N₄ or Pd/CeO₂.In the presence of 4 mL of benzyl alcohol,the corresponding conversion of benzyl alcohol and selectivity to benzaldehyde were 77%and 99%,respectively,under 90℃ of reaction temperature and at 5 h of reaction time.Moreover,the catalyst exhibited good generality in the selective oxidation reactions with various alcohols.