Structures and energetics of Pt clusters on TiO ₂: Interplay between metal-metal bonds and metal-oxygen bonds

Depositing size-selected nanoclusters on a well-defined support surface provides a way to probe the metal-support interaction and the size dependence of the catalytic activity; however, the detailed structural information at such interface is often missing. Here we examine from density functional theory the interfacial structure of Pt ₄ to Pt ₈ clusters on rutile TiO ₂(110). We find that Pt ₄ prefers a flat, nearly square structure on TiO ₂(110), while larger clusters such as Pt ₅, Pt ₆, Pt ₇, and Pt ₈ have a two-layer structure with the top layer not interacting with the support directly. The interaction strength generally increases with the contact area between Pt _n and TiO ₂(110). The interfacial structure is a result of optimizing the Pt-Pt, Pt-O, and Pt-Ti interactions: Pt ₄ prefers the square planar configuration on TiO ₂(110) with more Pt-Ti interaction over a two-layer, bi-triangle configuration of more Pt-Pt bonds; Pt ₈ prefers a hut-like two-layer structure over an edge-sharing bi-pyramid structure of greater internal strain. Our findings will be useful for understanding the interface of size-selected clusters on a typical reducible support such as TiO ₂ and its catalytic activity for reactions such as CO oxidation.