Interaction of CO with Pt nanoclusters on a graphene-covered Ru(0001) surface

The adsorption of CO on Pt nanoclusters on a single layer of graphene epitaxially grown on the Ru(0001) surface [Gr/Ru(0001)] was studied with reflection absorption infrared spectroscopy (RAIRS) and temperature programmed desorption (TPD). The graphene layer was grown through exposure to ethylene using a method that has previously been shown to completely cover the surface. As CO adsorbs on Ru(0001) but not on graphene, the complete coverage of the Ru(0001) surface by graphene was verified with TPD as no CO adsorption was detectable. Previous work has demonstrated that Pt nanoclusters nucleate in the moiré unit cells of the Gr/Ru(0001) surface. Exposure of the Pt/Gr/Ru(0001) surface to CO gives rise to strong RAIRS peaks at 2065-2085 cm^-1 assigned to CO at Pt atop sites and at 1848 cm^-1 due to CO at Pt bridge sites. The CO TPD peak areas were used to quantify the CO coverage, which allowed for the determination of the RAIRS peak areas per CO molecule. It was found that the RAIRS intensity for CO on Pt/Gr/Ru(0001) is as much as nine times the intensity of CO on Ru(0001) on a per molecule basis. A more modest intensity enhancement was observed compared to CO on Pt islands on the Ru(0001) surface.