First-Principle Study On Cu/Graphdiyne Catalysts For Low-Temperature CO Oxidation

The vast majority of carbon allotropes in nature are sp3 and sp2 hybrids.The separation and synthesis of new carbon allotropes is still a fast growing topic in carbon materials science.Graphdiyne is the first artificially-synthesized,sp-hybridized new carbon material.It has a highly conjugated surface,rich pore structure,flexible and easy-to-control electronic structure,which led to excellent material properties and performance.The research of graphdiyne can not only expand the family of carbon materials,but also enable scientists to understand the different chemical properties between sp hybridization and other hybrid forms deeply,which is of great significance to the design and development of new carbon materials in the future.Metal modification and heteroatom doping are effective methods to improve the performance of graphdiyne materials.Due to the difference in electronegativity between heteroatoms and carbon,doping will affect the charge distribution on the surface of graphdiyne.This difference in charge density will further promote the surface chemical activity.Sp-C of graphdiyne can coordinate and couple with metal atom.The interaction not only keeps the metal atoms highly dispersed,but also adjusts and optimizes their electronic structure.Therefore,graphdiyne can be used as excellent materials to prepare single-atom catalysts.Due to the uniform active sites and simple structure,single-atom catalysts not only can significantly improve the atom utilization efficiency,but also serve as a model catalyst for theoretical research.At present,there are relatively few studies on non-precious metal single-atom catalysts.Copper-based catalysts are cheap and easy to obtain,and have good CO catalytic activity,but the structure-activity relationship is still unclear.Therefore,this thesis uses CO as the probe molecule to study the structural properties of the copper/graphdiyne-based model catalyst and its reaction mechanism for CO oxidation under first-principle theoretical calculations.The details are as follows:Firstly,we established a SinCu/GDY catalyst model and found that the catalyst has good stability.Copper atoms are the active center,on which the co-adsorption configuration of CO and O2 is very stable.CO oxidation proceeds under the LH mechanism while its activity performance is not very impressive.The catalyst model of SinCu/3N-GDY and TriCu/GDY were further established,hoping to reduce the reaction barrier and improve the activity by introducing metal clusters or heteroatoms.Results have shown that SinCu/3N-GDY tends to follow TER mechanism.Nitrogen doping will change the geometry of graphdiyne,making the coordination environment of copper highly unsaturated.The substrate regulates the electronic structure of copper through Cu-N bonds.All these factors enhance the adsorption properties and its catalytic three-copper cluster is a stable load structure.The energy barrier of the LH mechanism is reduced due to the synergistic effect between atoms in the metal cluster,but the strong interaction between the copper cluster and the single oxygen atom makes the second molecule CO2 difficult to generate.In summary,this thesis systematically studied the copper/graphdiyne-based model catalyst,clarifying the interaction between copper atom and acetylene bonds and the CO oxidation reaction mechanism.Both the doping of nitrogen and the synergistic effect among the copper cluster atoms can enhance the catalytic activity.The research results of this thesis provide theoretical ideas for the design and development of a new type of copper/graphyne-based composite catalysts with low-temperature activity and stability and its application in gas-phase catalysis.