Theoretical Design And Study Of Oxidation Behavior Of Single-atom Catalysts In N-p Codoped Two-dimensional Materials

Single-atom catalysts?SACs?are the new concept in the heterogeneous catalysis community.It can be defined as the catalysts containing isolated metal atoms singly dispersed on supports with uniform activity.SACs maximize the efficiency of metal atom use,which is particularly important for supported noble metal catalysts.Moreover,with well-defined and uniform single-atom dispersion,SACs offer great potential for achieving high activity and selectivity.In addition,study of basis step in the reactions involving SACs can not only help us to understand the essence and mechanism of metal catalysis reactions,but also is very important to design new catalysis reactions.On the other hand,graphene,hexagonal boron nitride?h-BN?single layer and other two-dimensional materials have been used as promising catalyst supports for their large specific surface areas,novel electronic and thermal properties,and their close contact with catalysts.However,with the decreasing of particle size,the surface free energy increases obviously,and tends to aggregate into clusters or particles,which means that the SACs are difficult to fabricate in the two-dimensional materials.To enhance the interaction between metal atoms and two-dimensional materials,various vacancy defects,such as monovacancy,have been introduced into two-dimensional materials.However,precisely controlling of the vacancy formation is very difficult in experiments by atom or ion beam,which might lead to appearance of cluster distribution of the metal catalyst atoms.Hence,exploiting new strategy that can uniformly disperse the metal atoms on two-dimensional materials will be highly desirable.In this thesis,we suggest the n-p codoping method to enhance interaction between the metal adatoms and two-dimensional materials,and approve that n-p codoped two-dimensional materials are high catalytic activity and high stable SACs.The concept of n-p codoping may lead to new design strategy in large-scale synthesis of stable single-atom catalysts.The main works in this thesis are as the follows:1.We propose a concise and feasible n-p codoping approach,that can disperse the relatively expensive metal,copper?Cu?,onto boron?B?-doped graphene,effectively resulting in high-activity SACs.We use CO oxidation on B/Cu codoped graphene,as a prototype example,and demonstrate that:?1?a stable SAC can be fabricated by stronger electrostatic attraction between the metal atom?e.g.n-type Cu?and support?e.g.p-type B doped graphene?.?2?the energy barrier of the prototype CO oxidation on B/Cu codoped graphene is 0.536 eV by the Eley-Rideal mechanism.Further analysis shows that the spin selection rule theory can provide well theoretical explanation of high activity of our suggested SAC.This study approves that B/Cu codoped graphene is high catalytic activity and high stable SACs.2.In order to develop low-cost,green,and efficient catalysts,we find that the inexpensive metal,iron?Fe?,onto boron?B?-doped graphene based on n-p codoping approach,can effectively form stale and high-activity SACs.As a prototype example,we check CO oxidation reaction on B/Fe codoped graphene.It is firstly shown that well dispersed Fe atom can be realized with the help of stronger electrostatic attraction from the n-type Fe and p-type B doped graphene.Secondly,the maximum energy barrier of CO oxidation on B/Fe codoped graphene is 0.692 eV by the Eley-Rideal mechanism.Further analysis indicates that spin state of the O₂ play an important role in the CO oxidation on B/Fe codoped graphene.This study approves that B/Fe codoped graphene is high catalytic activity and high stable SACs.3.The thermal stability and chemical reactivity issues associated graphene may hinder its application.Alternatively,the h-BN monolayer is a wide band gap semiconductor with high chemical and thermal stability.The O₂ activation and CO oxidation behaviors on the n-p codoped hexagonal boron nitride?h-BN?monolayer have been systematically investigated by first-principles calculation.It firstly shows that the stable single-atom catalysts can be formed with the help of stronger electrostatic attraction from the n-type metals?Fe,Cu,Pd,Ag,Ir,Pt,and Au?and p-type C doped h-BN monolayer.Secondly,the obviously elongated O-O bond of O₂ suggests that it has been well activated on n-p codoped h-BN monolayer.As a prototype example,we check CO oxidation reaction on C/Cu codoped h-BN monolayer and find that the maximum energy barrier of CO oxidation is 0.655 eV by the Eley-Rideal mechanism.Furthermore,the strongly hybridization between Cu 3d and O₂ 2p orbitals is found to plays a crucial role in the CO oxidation on n-p codoped h-BN monolayer.This study approves that C/Cu codoped graphene is high catalytic activity and high stable SACs.4.Exotic and robust metallic surface states of topological insulators?TIs?have been expected to provide a promising platform for novel surface chemistry and catalysis.We firstly study the adsorption stability of O₂ on the surface of Bi₂Se₃ and find a more stable configuration than that obtained from a previous study.But its adsorption energy is only-0.12eV.Using natural V_Se vacancy in the surface of Bi₂Se₃,we study the catalytic properties of metal?Fe,Cu,Rh,Pd,Ag,Ir,Pt,and Au?embedded Bi₂Se₃.It is found that the maximum energy barrier of CO oxidation on Au embedded Bi₂Se₃ is 0.61 eV by the Eley-Rideal mechanism.For the Pt embedded Bi₂Se₃,the maximum energy barrier of CO oxidation is 0.54eV by the Eley-Rideal mechanism.Further analysis indicates that spin state of the O₂ play an important role in the CO oxidation on metal embedded topological insulator SACs.This study approves that Au and Pt embedded Bi₂Se₃ films are high catalytic activity and high stable SACs.