(91a) Density Functional Theory Study of the Initial Oxidation of the Pt(111) Surface

Expanding the fundamental understanding of catalytic behavior under oxygen-rich conditions on transition metal surfaces, such as Pt(111), has recently garnered interest, since the ability to operate internal combustion engines in fuel-lean, oxygen-rich environments could lead to dramatic improvements in fuel efficiency. However, new catalysts capable of handling the increased NOx emissions would be required. One area of particular importance in the development of such catalysts is to understand the transition of oxygen phases on metal surfaces from chemisorbed oxygen to surface and bulk oxides, since these oxide phases can have dramatically different reactivity. We have used density functional theory (DFT) calculations to examine the initial stages of oxidation of the Pt(111) surface and have determined that subsurface oxygen is not the precursor to oxidation. Instead, we predict a strong preference for the formation and growth of one-dimensional Pt oxide chains within the p(2×1) structure which exhibit large buckling and modification of the charge of the surface Pt atoms. Furthermore, half of the oxygen atoms in the Pt oxide chains reside near hcp sites, contrary to reports that oxygen atoms reside only on fcc sites on Pt(111). Our results agree well with a recent scanning tunneling microscopy study and suggest a precursor mechanism to the oxidation of metal surfaces involving Pt oxide chain formation and growth on terraces at moderate oxygen coverages. We will also briefly discuss the implications of these new structures to current models of CO and NO oxidation on Pt(111).