Synthesis Of Oxide-based Pd Single Atom Catalysts And Investigation Of Selective Hydrogenation Mechanisms

With the progress of science and technology,how to improve efficient energy utilization has become a hot topic in science.Recently,the supported single atom catalysts with their unique electronic,geometric structure and high atomic utilization in heterogeneous catalysis exhibit excellent catalytic activity and high selectivity.In this thesis,we developed simple and efficient synthetic methods to construct isolated Pd atoms on two metal oxides,being cerium oxide nanorod(Pd₁/Ce O_2-x)and cubic indium oxide(Pd₁/In₂O_3-x),respectively.The two catalysts showed good activity in selective hydrogenation reactions.The main research contents are summarized as follows:1.A simple spatial confinement strategy was developed to create atomically dispersed palladium atoms supported over defect-containing porous ceria nanorod,with palladium loading up to 0.26 wt.%.The existence of singly dispersed palladium atoms is confirmed by spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements.This catalyst shows excellent efficiency in hydrodehalogenation reactions at low H₂ pressure under mild conditions（1 atm H₂,80℃）,giving rise to satisfactory recyclability and scalability.Density functional theory（DFT）calculations reveal that the high activity stems from the modified electronic structure and metal-support interactions of palladium confined in defect-containing ceria nanorod.2.A straightforward high-temperature quenching method was employed to precisely construct isolated palladium atoms supported over cubic indium oxide,with individual palladium atoms coordinated with four neighboring oxygen atoms.The presence of atomically dispersed palladium atoms is evidenced by a library of advanced characterizations and density functional theory（DFT）calculations.The Pd₁/In₂O_3-x catalyst achieves exceptional catalytic efficiency（1 atm H₂@20℃）in the selective hydrogenation of nitrobenzene to aniline,with more than 99%chemoselectivity under almost 100%conversion.The turnover frequency（TOF）is calculated to be as high as 4286 h^-1.Moreover,it delivers excellent recyclability,storage stability,and substrate tolerance.DFT calculations further reveal that the high catalytic activity stems from the optimized electronic structure and the charge state of single palladium atoms in the defect-containing indium oxide.