Carbon monoxide oxidation on bare and Pt-modified Ru(101̄0) and Ru(0001) single crystal electrodes

Carbon monoxide oxidation on bare and Pt-modified ruthenium surfaces with the (101̄0) and (0001) orientations was investigated with cyclic voltammetry, scanning-tunneling microscopy and in situ Fourier transform infrared spectroscopy. Facile oxidation kinetics of CO on Ru(101̄0) are observed, in contrast with a slow reaction on Ru(0001). Scanning tunneling microscopy (STM) measurements confirmed that spontaneous deposition of Pt produces island-like structures on both single crystal Ru surfaces. CO oxidation on a bimetallic Pt/Ru(101̄0) surface with a Pt coverage of approximately one monolayer occurs at potentials that are 140 mV more negative than those for bare Pt. This potential is, however, more positive than the potential of the onset of the oxidation on Ru(101̄0). IR spectroscopy shows one peak for linearly adsorbed CO on bare and Pt-modified Ru(101̄0) surfaces, while two peaks are visible for the Pt-modified Ru(0001) structure. A single broad peak for the bimetallic Pt/Ru(101̄0) surface may result from addition of the red-shifted peak for Pt and the peak for the Ru(101̄0) substrate. A large red shift of CO on the Pt/Ru(101̄0) surface requires further work to be explained. A negative shift of CO oxidation on Pt/Ru(101̄0) indicates a decrease of the PtCO bond strength on that surface compared with the bond with bulk Pt.