Interaction of Pt clusters with the anatase TiO2(101) surface:: A first principles study

The adsorption of Pt-n (n = 1-3) clusters oil the defect-free anatase TiO2(101) surface has been studied using total energy pseudopotential calculations based on density functional theory. The defect-free anatase TiO2-(101) surface has a stepped structure with a step width of two O-Ti bond distances in the (100) plane along the [10 $$(1) over bar] direction and the edge of the step is formed by 2-fold-coordinated oxygen atoms along the [010] direction. For a single Pt adatom, three adsorption sites were found to be stable. Energetically, the Pt adatom prefers the bridge site formed by 2 2-fold-coordinated oxygen atoms with an adsorption energy of 2.84 eV. Electronic structure analysis showed that the Pt-O bonds formed upon Pt adsorption are covalent. Among six stable Pt-2 adsorption configurations examined, Pt-2 was found to energetically favor the O-O bridge sites on the step edge along [010] with the Pt-Pt bond axis perpendicular to [010]. In these configurations, one of the Pt atoms occupies the same O-O bridge site as for a single Pt adatom and the other one either binds a different 2-fold-coordinated oxygen atom on the upper step or a 5-fold-coordinated Ti atom on the lower terrace. Three triangular and three open Pt-3 Structures were determined as minima for Pt-3 adsorption on the surface. Platinum trimers adsorbed in triangular structures are more stable than in open structures. In the most stable configuration, Pt-3 occupies the edge O-O site with the Pt-3 plane being upright and almost perpendicular to the [001] terrace. The preference of Pt,, to the coordinately unsaturated 2-fold-coordinated oxygen sites indicates that these sites may serve as nucleation centers for the growth of metal clusters on the oxide surface. The increase in clustering energy with increasing size of the adsorbed Pt clusters indicates that the growth of Pt oil this surface will lead to the formation of three-dimensional particles.