Structures And Small Molecules Adsorption On Au/Pd Alloy Clusters And Hydrogen-doped Au-clusters:A DFT Investigation

The rapid development of industry and transportation to the environment caused by increasingly serious pollution,carbon monoxide CO and nitrogen oxide NOx emissions are the largest atmospheric pollutants,so there is an urgent need to research and development of CO oxidation and NO reduction of new efficient catalyst.In recent years,alloy nanoclusters as catalysts have attracted great interest,among which au-Pd alloy clusters show better catalytic performance than pure gold and pure palladium clusters,although some progress has been made in catalytic oxidation of CO and reduction of NO.There is still much room for research on the effect of the structure of bimetallic AuPd alloy clusters and different Au/Pd ratios on the surface catalytic activity of the clusters.In addition,based on the gold-hydrogen analogy proposed by Kiran et al.,the effect of hydrogen mixing on the electronic structure and catalytic activity of gold clusters has attracted the attention of experimental and theoretical workers.The electronic structure of clusters and the interaction between clusters and adsorbents are the key to understanding the catalytic performance.The electronic structure of clusters and the interaction between clusters and adsorbents are the key to understanding the catalytic performance.Quantum chemical calculation studies can explore the relationship between the structure of nanoclusters and the influence on the activation of small molecules from a microscopic perspective,which is conducive to finding more efficient nanocluster catalysts.In this paper,the electronic structure calculation based on density functional theory,eight-atom AumPdn(m+n=8)clusters as the model system,and the crystal structure prediction program CALYPSO based on particle swarm optimization algorithm are used to construct various kinds of gold-palladium alloy clusters of different proportions.The total energy is calculated and the structure is optimized by the quantization program of DMol3,the first principle cluster calculation method.The dynamic stability of the structures is tested by vibration frequency analysis.The lowest energy state structure is determined and the electronic structure is analyzed in detail.The adsorption and dissociation process of NO gas molecules on AumPdn(m+n=8)clusters was investigated.The adsorption properties of CO molecules were investigated to prepare for the exploration of catalytic oxidation of CO.Finally,the structure effect of hydrogen-doped gold clusters was verified by using the eight-atom gold cluster as the model,and the adsorption and deionization of small gas molecule NO was studied on the lowest energy state structure of Au7H cluster.The main conclusions of the above work are as follows:1.The PBE exchange correlation functional under the generalized gradient approximation(GGA)was used to obtain the lowest energy state structure of AumPdn(m+n=8)clusters at the DNP base group level.By calculating the average bond length of clusters,binding energy,mixing energy and atomic vibration frequency,it was found that alloying made the structure more compact without virtual frequency.It shows that the lowest energy state structure has good thermal and kinetic stability,and Au5Pd3 cluster is relatively stronger.The calculation and analysis of the bias density(PDOS)of pure and alloy clusters show that the D-band center(εd)of the introduced Pd atomic cluster increases obviously,and the εd of Au5Pd3 cluster is closest to the Fermi level,which enhances the interaction between the surface and adsorbated molecules.2.Gauss 09 quantization package was used to calculate the electronic structure of the system at GGA-PBE/LANL2DZ level,and Multiwfn combined with VMD analysis was used to plot the bond critical point(BCP)and molecular electrostatic potential(MESP)of the AumPdn system.The average bond critical point density of Au5Pd3 cluster was the highest.The predicted ratio of 5/3 Au/Pd alloy is beneficial to improve the bonding strength between atoms.The analysis of molecular electrostatic potential predicts the possible active adsorption sites of small gas molecules.The top potential of Pd atom in alloy cluster is negative,which is an electron-rich region with electrophilic activity.3.Studies on the adsorption performance of small gas molecules NO on AumPdn clusters show that alloying enhances the adsorption energy of small gas molecules NO compared with pure clusters.The best adsorption site on alloy clusters is the top of Pd atom,and the activation of NO bond provides a possibility for NO dissociation.4.The dissociation process of NO on AumPdn(m+n=8)cluster was studied by direct reduction method of NO.The transition state was searched by LST/QST method,and the transition state was determined by frequency analysis.The results showed that Au5Pd3 cluster had the lowest catalytic reaction barrier(0.48eV).5.The calculation of different adsorption sites of small molecular gas CO on AumPdn(m+n=8)cluster shows that,compared with pure Au8 cluster,the alloy cluster has stronger adsorption energy for CO.At the most favorable adsorption site,the top position of Pd atom changes from physical adsorption to chemical adsorption,and C-O bond is activated.The CO adsorption energy of Au3Pd5 cluster is the largest,and the tensile vibration frequency of C-O bond is the smallest.This work lays a foundation for the study of catalytic oxidation of CO.6.The PBE exchange correlation functional under GGA was used to obtain the lowest energy state structure of hydrogen-doped gold cluster Au7H at the DNP base group level.The average bond length,binding energy,mixing energy and atomic vibration frequency of the clusters were calculated,and it was found that hydrogen-doped gold cluster made the structure more compact without virtual frequency.This indicates that the lowest energy state structure has good thermal and kinetic stability,and the stability of Au7H-a cluster is relatively stronger.The three-dimensional isomers of the Au7H-a cluster are most similar to the pure Au8 cluster,confirming the gold-hydrogen analogy.7.Studies on the adsorption performance of small gas molecule NO on Au7H clusters show that hydrogen doped small gas molecule can enhance the adsorption energy of NO compared with pure gold clusters.The optimal adsorption site on hydrogen-doped gold clusters is the top position of low coordination Au atom,the stretching vibration frequency OF the adsorption molecule NO decreases,and the activation of NO bond provides the possibility for NO dissociation.