Density Functional Theory Study Of Platinum-iridium Binary Alloy Clusters And Its Adsorption Of Micromolecule

In this paper,geometric and physicochemical properties of Pt_mIr_n?m+n=2-10?clusters and Pt_mIr_nNO?m+n=2-10?clusters have been systematically calculated and studied based on density functional theory?DFT?with considering the generalized gradient approximation?GGA?level in Dmol³ software package.The main contents are as follows:?1?The results of study of Pt_mIr_n?m+n=2-7?clusters show that:most of doped clusters use the ground state structures of pure Ir_n clusters as basic structural units.The analysis of average atomic binding energies shows that the addition of iridium atoms improves the stability of pure platinum clusters.The second-order energy difference curves of Ir_n and Pt_1,2Ir_n clusters exist even-odd oscillations.Pt_2,5,Pt_1-3Ir and Ir_2,3,7 clusters show higher energy gaps than other clusters,illustrating that these clusters are stronger in chemical stability.The distribution of d orbital electrons of all clusters are relatively localized.The total density of states mainly come from contribution of d orbital in the range of-5-2eV.For Pt_1,3Ir₃,Pt₄Ir_1-2,Pt₂Ir₄,PtIr₅,and Ir₇ clusters,there are a large number of electron spin density around each atom,indicating that each atom in clusters contributes a great deal to local magnetic moment.?2?The results of study of the Pt_mIr_nNO?m+n=2-7?cluster show that:the NO molecule is attached to a single metal atom via the N atom in all ground state structures.In the doped clusters,NO molecule prefers to be adsorbed near the Ir atom top site than the Pt atom.Adsorption energies studies show that the addition of an appropriate amount of Ir atoms in pure Pt clusters improves the adsorption strength of clusters.And the adsorption energy of bimetallic Pt_mIr_nNO?m+n=2,4,6?clusters is larger than that of pure clusters with the same cluster size,showing that the interaction of even alloy clusters and NO molecule are stronger.There exist clear even-odd oscillations on second-order energy difference curves of the Pt_mIrNO and PtIr_nNO clusters.It is obvious that there exist odd-even oscillations in the energy gap curves of m+n=3,4 and 6,indicating that the peaks cluster are stronger in chemical stability.The spd hybridization not only occurs in different orbits,but also occurs between different atoms.?3?The results of study of the Pt_mIr_n?m+n=8-10?cluster show that:simple cube structure is expected to be an effective basic structural units for Ir-rich clusters.The second-order energy difference of the Pt_4-6Ir₄,Pt₆Ir₂,Pt₇Ir_1-2,Pt_1-2Ir₈,and Pt₄Ir₆ clusters are large relative to other clusters,which means that these clusters are more stable.The second-order energy difference curve of Pt_nIr_?9-n?clusters shows the evident even-odd oscillations,suggesting that PtIr₈,Pt₃Ir₆,Pt₅Ir₄,and Pt₇Ir₂ clusters are more stable than their neighbor clusters.The minimum excess energies values are seen for Pt₇Ir,PtIr₈ and Pt₂Ir₈,indicating that these clusters have stronger stabilities.The results of study of NO adsorbed into Pt_mIr_n?m+n=8-10?clusters show that:NO molecule is adsorbed on the top site of all bare cluster via the N atom.Moreover,NO molecule prefers to be adsorbed on the Ir atom in all alloy clusters,which is consistent with the result of Pt_mIr_nNO?m+n=8-10?clusters.By analyzing the adsorption energy of Pt_mIr_nNO?m+n=8-10?clusters,it can be found that the peak of each size is corresponding to the Pt₅Ir₃NO,Pt₂Ir₇NO and PtIr₉NO,respectively.This illustrates that the combination of NO molecules are better than those of their neighbors.The adsorption energy of bimetallic Pt_mIr_nNO?m+n=8?except Pt₂Ir₆NO is larger than that of8-atom pure clusters,suggesting that the interaction of 8-atom alloy clusters and NO molecule are stronger.The second-order energy difference curves of Pt_nIr_?N-n?NO?N=8-10?clusters show the evident even-odd oscillations.The maximum values of energy gap are seen for PtIr₇NO,Pt₇Ir₂NO and Pt₅Ir₅NO with the same cluster size,indicating that these clusters are stronger in chemical stability.The surface adsorption properties and reactivity of binary alloy clusters are more dominants than those of pure clusters,showing that binary alloy clusters have great potential in the field of catalysts.Therefore,the study of platinum-iridium binary alloy clusters and its adsorption of micromolecule has great research value and application prospect.