The properties of Irn (n = 2–10) clusters and their nucleation on γ-Al2O3 and MgO surfaces: from ab initio studies

Abstract

The structural stability and magnetic properties of iridium clusters Ir_n (n = 2–10) and their interaction on γ-Al₂O₃(001) and MgO(100) surfaces have been investigated from first principles calculations. It is found that the adsorption energy of Ir_n (n = 2–10)/γ-Al₂O₃(001) is lower than that of Ir_n/MgO(100); meanwhile, the strongest adsorption energy cluster for γ-Al₂O₃(001) is the tetrahedral Ir₄ cluster, while for MgO(100) is a cubic Ir₈ cluster. On the other hand, the nucleation of Ir_n (n = 2–10) clusters on both surfaces is thermodynamically favorable and exothermic. Moreover, the nucleation energy of Ir_n (n = 2–10) clusters on the γ-Al₂O₃(001) surface is close to the corresponding energy on the MgO(100) surface, except for Ir₃, Ir₄ and Ir₆ clusters. Interestingly, the nucleation of Ir₃ and Ir₆ clusters on the MgO(100) surface is more favorable than that on the γ-Al₂O₃(001) surface, while the nucleation of the Ir₄ cluster is reverse and very close to the gas phase Ir₄ cluster. More importantly, deformation energy and charge density analysis show that the adsorbed Ir₄ cluster on the γ-Al₂O₃(001) surface has obviously charge transfer between Ir atoms and surface Al, O atoms with negligible deformation. However, for the MgO(100) surface, the Ir₄ cluster connects directly to three surface O atoms with severe distortion, which inhibits the activity of the tetrahedral Ir₄ cluster as a catalyst.