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

Little is known about the detailed structural information at the interface of Pt cluster and γ-Al₂O₃(001) surface, which plays an important role in the dehydrogenation and cracking of hydrocarbons. Here, the nucleation and growth of Pt (n = 1-8, 13) clusters on a γ-Al₂O₃(001) surface have been examined using density functional theory. For the most stable configuration Pt /γ-Al₂O₃(001) (n = 1-8, 13), Pt clusters bond to the γ-Al₂O₃(001) surface through Pt-O and Pt-Al bonds at the expense of electron density of the Pt cluster. With the increase in the Pt cluster size, both the metal-support interaction and the nucleation energies exhibit an odd-even oscillation pattern, which are lower for an even Pt 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.