Catalysis Of Single-Atomic-thick Pd_N Motifs Stabilized On Defect-free MoS₂/Metal Heterostructure:First-principles Calculations

With the rapid development of modern catalysis science,transition metal（TM）and noble metal（NM）of Nanoparticles（NPs）or nanoclusters（NCs）catalysts are widely used in industrial production and applications cause of unsaturated coordination bond and higher chemical activity.However,due to the non-uniform,complex,dynamic structure and other uncertain factors in nanoparticles,in practice,a variety of different reactive active site are often generated,resulting in unnecessary side reactions.In the past decade,with the improvement of preparation methods and theortical research,scientists have highly dispersed nano-transition metal particles to form atomic clusters,and even"single-atom"highly discrete single-atom systems,namely"single-atom catalysts"（SACs）.Highly efficient single-atom scale catalysts stabilized on appropriate substrate have high catalytic efficiency and selectivity for many chemical reactions.As a new generation of economic and efficient catalysts with important industrial application prospects,it is of great practical significance to develop SACs with high stability on suitable substrates.Here,first-principles calculations are performed to report a synergetic role of charge transfer and strain engineering in significantly improving the stability and catalysis of single-atom-thick two-dimensional（2D）Pd₃motif on MoS₂/Au（Ag）（111）heterostructures.This result can provide important theoretical guidance for the experimental preparation of a stable single-atom catalyst on MoS₂and changing its catalytic performance.This thesis expands the specific narrative through the following chapters:Chapter 1 is the introduction section,we introduce the background knowledge related to the field of catalysis and the oringin and development of single atom catalysts（SACs）,and briefly describes the achievements of SACs in terms of catalytic performance and the development prospects and development prospects of SACs in this field.difficult.Then we elaborated various strategies for dispersing atoms on MoS₂,and the research progress of forming stable single atom catalysts on defect-free MoS₂.Chapter 2 is the theory and methods section.As an emerging discipline,in this chapter,we mainly introduce the first-principles calculation method based on density-functional theory.Starting from the Schrodinger equation in quantum mechanics,we briefly explain the calculation process,and finally listed the modeling and analysis software needed.In chapter 3,First of all,we applied tensile strain to the single-layer defect-free MoS₂ or covered it on Au（Ag）（111）substrate.With the monolayer defect-free MoS₂epitaxially covered on Au（Ag）（111）,the lattice mismatch can induce tensile strain on MoS₂ and their contrast work functions results in charge transfer from the metal substrates to the MoS₂ overlayer.The synergistic effect of tensile strain and charge transfer can significantly reduce the band gap of MoS₂ and cause a phase transition from semiconductor to metal.Such a synergetic effect enlarges the binding energy and diffusion barrier of Pd on MoS₂,which facilitates the atomic dispersion of the Pd adatoms on MoS₂,forming 2D-Pd _N magic nanomotifs with downward shifted d-orbital states beneficial the enhancement of O₂ activation and reduction of CO poisoning.In chapter 4,taking 2D-Pd₃as a typical example,we adsorbed CO and O₂ on the active sites of Pd₃ on four substrates,and did a systematic study on the adsorption behavior of two gaseous molecules description.Next,by analyzing the adsorption energy of the two molecules on the active sites of Pd₁ and Pd₃,combined with the DOS diagram,we propose that there may be two main catalytic mechanisms,TER mechanism and CLH mechanism of the CO oxidation reaction,at two different gas concentrations.We find that the CO oxidation reaction process can be carried out on one Pd（TER mechanism）or two Pd（CLH mechanism）active sites in 2D-Pd₃.Other Pd atoms will participate in the oxidation reaction by providing electron.And Pd₃/MoS₂/Ag（111）has a very low reaction barrier（0.4～0.6 e V）.This study improves both the stability and catalytic activity of Pd₃ through the charge transfer and strain engineering,and in turn greatly reduces the reaction potential barrier.The present findings are expected to pave a new avenue toward design of highly efficient new type of SACs on MoS₂-based functional heterostructures.