From adlayer to surface alloy - change in chemical properties of bimetallic PtRu/Ru(0001) surfaces

The chemical and catalytic properties of bimetallic surfaces are of high interest as model systems for bimetallic catalysts. We studied the influence of the structural properties of PtRu/Ru(0001) model systems on their chemical properties. STM measurements show a change of the surface morphology in dependence of the deposition/annealing temperature. Deposition of Pt at room temperature (300 K) leads to dendritic Pt islands, while heating to 700 K results in rounded Pt islands. Annealing to even higher temperatures leads to the gradual formation of a surface alloy, which is completed at 1300 K. This surface alloy is characterised by a statistical distribution of the constituents in the surface layer. The change of the structural properties induces changes in the chemical surface properties, which were tested by the interaction of CO and D2 with the model surfaces. The CO and D2 TPD spectra show a redistribution of the intensity in the desorption peaks due to the modification of the surface structure. The influence of the surface structure is also evidenced in IR spectra of CO adsorbed on the model surfaces. We correlate the change of the chemical properties of the bimetallic PtRu/Ru(0001) model systems to the modification of the structural properties and explain the variation of the chemical properties in terms of ligand, ensemble, and strain effect