Theoretical Study On The Reaction Mechanism Of Metal Doped Two-Dimensional Materials For N₂ Reduction And CO Oxidation

Single atom catalysts have very high metal atom utilization and excellent reaction selectivity,and can improve the active site density of single atom and then to regulate the carrier materials'surface properties.Two-dimensional materials have many unique physical and chemical properties,they can be directly used as catalysts for reactions,and they are also excellent catalytic carriers.Therefore,we combine two-dimensional materials with metal atoms in an attempt to form a single atom catalyst with metal-doped two-dimensional materials,it may has the highest metal utilization property.Then,using the density functional theory to study the catalytic activity and mechanism of the above single atom catalysts for N₂ reduction and CO oxidation.The main research work and results are as follows.1.Using the density functional theory to study the catalytic activity of the metal atoms?M=Sc-Zn,Y-Cd,Li-Na,Be-Ca,Al-In,Ge-Sn?embedded in boron monolayer to the synthesis reaction of ammonia.The results show that among all the 30 catalysts we studied,Mo@BM-?₁₂ has the highest catalytic activity,and the onset potential is only 0.26 V when NRR electrocatalyzed by enzymatic mechanism.Moreover,when the NRR reaction was carried out on Mo@BM-?₁₂,the onset potential of the side reaction HER was larger than NRR,indicating that the probability of the side reaction was extremely low.It is also found that between the three catalysts of Cr@BM-?₁₂,Mn@BM-?₁₂ and Tc@BM-?₁₂ in NRR catalyzing reaction,the absolute value of minimum onset potential is less than 0.5 V.This work may provide a new idea for the design of catalyst in NRR and demonstrate that boron monolayer can be used as excellent catalyst substrates.2.Using density functional theory to screen the non-precious transition metals?Sc,Ti,V,Cr,Mn?embedded in graphene as single atom catalysts for CO oxidation reaction.Based on the binding energy between the metal atom and the graphene substrate,the diffusion barrier of the metal atom on graphene,and the results of the reaction barrier by analysing the transition state,it is found that Mn-graphene has the excellent catalytic activity for CO oxidation reaction.It is also found that Sc,Ti,V,and Cr embedded in graphene can adsorpt O₂ too strongly which may leads to oxygen poisoning.So we expect that Mn-graphene should be fabricated experimentally,and predict that it maybe a new stable and efficient single-atom catalyst.For Mn–graphene,the Langmuir–Hinshelwood?LH?and Eley–Rideal?ER?mechanisms of CO oxidation reaction have been researched.It is found that the CO molecules cannot interact with O₂,which activated on graphene surface,to form carbonate-like CO₃ complexes or other intermediates.It indicated that CO oxidation reaction will not proceed via the ER mechanism.It is also found that the reaction mechanism for CO oxidation reaction on the Mn-graphene has two steps:first is the LH mechanism CO+O₂?OCOO?CO₂+O,and then followed by the ER mechanism CO+O?CO₂.The energy barriers are 0.57-0.69 eV and 0.08 eV respectively which are close to or smaller than CO oxidation reaction on the Ni-graphene or Mo-graphene,indicating the Mn-graphene has the higher activity.At last,a simple molecular dynamics simulation is performed on Mn-graphene system.It is found that Mn-graphene can be exsisted as a single atom catalyst and can catalyze CO oxidation reaction over a broad range of temperatures.This work may provide a new idea for the synthesis of the new type single atom catalysts.