Quantum-chemical calculations of CO and OH interacting with bimetallic surfaces

In this work we present results of a periodic density-functional theory study of the adsorption of carbon monoxide (CO) and hydroxyl (OH) on platinum-ruthenium, platinum-molybdenum and platinum-tin alloys as well as the adsorption of CO on a series of transition metals modified with a Pt overlayer. The surfaces are modelled as four-layer slabs (three-layer slab in case of Pt3Sn(111)). The binding energies and geometries of CO and OH are computed. In the case of PtRu, the mixing of Pt by Ru leads to a weaker bond of both CO and OH to the Pt sites, whereas mixing of Ru by Pt causes a stronger bond of CO and OH to the Ru sites. The binding energy trends for CO do not show a clear-cut relationship with its vibrational characteristics. The mixing of Pt by Mo leads to weakly adsorbed CO on both Pt and Mo sites, and OH strongly adsorbed only on Mo sites. This suggests that PtMo could be a better bifunctional catalyst for CO oxidation then PtRu. On Pt3Sn(111) the calculations show that CO binds only to Pt and not to the Sn, whereas OH has an energetic preference for the Sri sites. This also implies that PtSn should be a good CO oxidation catalyst. For Pt-monolayer systems, we demonstrate a relationship between the Pt-Pt distance in the monolayer and the changes in the CO binding energy. The nature of the substrate seems to be of secondary importance. (C) 2002 Published by Elsevier Science Ltd.