CO adsorption on the Pt/Rh(100) surface studied by high-resolution photoemission

Submonolayers of platinum have been deposited on an Rh(100) substrate. Platinum growth and subsequent CO adsorption on the bimetallic surface has been studied by high-resolution photoemission applying synchrotron radiation. Platinum was found to grow as small, single-layer islands on Rh(100). The CO adsorption site on both metals is very sensitive to compositional changes in the bimetallic surface. A site switch from on-top to bridge sites in the c(2×2) CO overlayer on Rh(100) has been observed in the presence of 0.2 monolayers (ML) of platinum. The CO saturation coverage is found to decrease dramatically with increasing platinum coverages. 0.9 ML of platinum on Rh(100) binds approximately half the CO bound by Pt(100). We explain this in terms of a reduced COPt bond strength through a ‘ligand effect’.