Density Functional Theory Study on the Nucleation and Growth of Pt n Clusters on γ-Al2O3(001) Surface.

Abstract

Little is known about the detailed structural information at the interface of Ptn cluster and γ-Al2O3(001) surface, which plays an important role in the dehydrogenation and cracking of hydrocarbons. Here, the nucleation and growth of Ptn (n = 1–8, 13) clusters on a γ-Al2O3(001) surface have been examined using density functional theory. For the most stable configuration Ptn/γ-Al2O3(001) (n = 1–8, 13), Ptn clusters bond to the γ-Al2O3(001) surface through Pt–O and Pt–Al bonds at the expense of electron density of the Ptn cluster. With the increase in the Ptn cluster size, both the metal–support interaction and the nucleation energies exhibit an odd–even oscillation pattern, which are lower for an even Ptn cluster size than those for its adjacent odd ones. Both the metal–surface and metal–metal interactions are competitive, which control the nanoparticle morphology transition from two-dimension (2D) to three-dimension (3D). On the γ-Al2O3(001) surface, when the metal–support interaction governs, smaller clusters such as Pt1, Pt2, Pt3, and Pt4 prefer a planar 2D nature. Alternatively, when the metal–metal interaction dominates, larger clusters such as Pt5, Pt6, Pt7, Pt8, and Pt13 exhibit a two-layer structure with one or more Pt atoms on the top layer not interacting directly with the support. Herein, the Pt4 cluster is the most stable 2D structure; Pt5 and Pt6 clusters are the transition from the 2D to the 3D structure; and the Pt7 cluster is the smallest 3D structure.