Theoretical Study Of The Effect Of Iridium Doping On The Structure,stability Of Silver Clusters And Its Activation Of Oxygen And Methane

As the main component of natural gas,methane is a clean and efficient energy source.Due to the high energy of the C-H bond during the cleavage of methane,the dehydrogenation reaction of methane is difficult to occur under mild conditions.Using silver clusters as the active catalyst for methane activation can significantly improve the efficiency of methane dehydrogenation.Further,the adsorption and dissociation of oxygen on silver clusters has been extensively studied because of its unique stability and catalytic properties.In recent years,the research on clusters is not limited to pure metal clusters.Doped atoms can change the structure of the original cluster and thus change its physical and chemical properties.Compared with pure silver clusters,doped clusters have better catalytic performance.And the oxygen atoms adsorbed on the clusters can affect the performance of the transition metal clusters to dissociate methane.Therefore,studying the effect of doping a iridium atom into silver clusters on the activation of oxygen as the cluster size increases,and studying the effect of doping a iridium atom into silver clusters and oxidation on the activation of methane as the cluster size increases can provide important theoretical guidance for the rational design of efficient and economical catalysts.Based on the density functional theory,Calypso software and Minima-hopping search method,this thesis studies the ground state structure,stability,oxygen adsorption and dissociation properties of Ag_n and Ag_n-1Ir（3-26）clusters.In addition,this thesis compares the performance of methane dissociation on the Ag_n,Ag_n-1Ir and Ag_nO₂（3-26）clusters.The purpose is to explore the effect of doping an iridium atom into silver clusters on the activation of oxygen and the effect of doping an iridium atom into silver clusters and oxidation on the activation of methane to provide theoretical guidance for related experiments.The main research contents and results of this paper are as follows:（1）Compare the ground state structure of Ag_n and Ag_n-1Ir clusters,it is concluded that doping Ir atom into Ag_nclusters can change the structure of the clusters.Calculate and compare the average binding energy,second-order energy difference and HOMO-LUMO gap of Ag_n and Ag_n-1Ir clusters,and it is concluded that each system of Ag_n-1Ir clusters is more stable than Ag_n clusters.For Ag_n clusters,Ag₆,Ag₈,Ag₁₄,Ag₁₈ and Ag₂₀ clusters have better stability,and for Ag_n-1Ir clusters,Ag₉Ir clusters and Ag₁₁Ir clusters have better stability.（2）Compare the oxygen adsorption and dissociation performance of Ag_n and Ag_n-1Ir clusters.When n is less than or equal to 10,the doped Ir atoms are fully exposed,the oxygen adsorption performance of Ag_2-9Ir cluster is much better than that of Ag_3-10 cluster,and the oxygen dissociation energy barrier of the Ag_2-9Ir clusters is much smaller than that of Ag_3-10 clusters.Compared with the Ag_3-10 clusters,the Ag_2-9Ir clusters have better oxygen adsorption and dissociation performance.When n is greater than 10,the doped Ir atoms are gradually surrounded,the difference between the oxygen adsorption energy and the oxygen dissociation energy barrier of Ag_10-25Ir clusters and the oxygen adsorption energy and the oxygen dissociation energy barrier of Ag_11-26 clusters is relatively small,the doped clusters have similar activities with those pure sliver clusters.（3）Compare the performance of Ag_n and Ag_nO₂ clusters for dissociating methane,the methane dissociation energy barrier and endothermic energy value of Ag_nO₂ clusters are much lower than that of Ag_n clusters.The oxygen atom promotes the dissociation of methane on the Ag_n cluster.Compare the performance of Ag_n and Ag_n-1Ir clusters for dissociating methane,when n is less than or equal to 8,the doped Ir atoms are fully exposed,and the methane dissociation energy barrier and endothermic energy value of the Ag_2-7Ir clusters is much lower than that of Ag_3-8clusters.Compared with Ag_3-8 clusters,Ag_2-7Ir clusters have better catalytic performance for the activation of methane.When n is greater than 8,doped Ir atoms cannot be used as active centers.The difference between the methane dissociation energy barrier and endothermic energy value of Ag_8-25Ir clusters and the methane dissociation energy barrier and endothermic energy value of Ag_9-26 clusters are very small,the doped clusters have similar activities with those pure sliver clusters.