ADSORPTION OF CO ON ORDERED ALLOY SURFACES

The adsorption of CO on two ordered alloy surfaces, Cu{001}c(2 x 2)-Pd and Ni{001}c(2 x 2)-Al, has been studied by high-resolution electron-energy-loss spectroscopy. For Cu{001}c(2 x 2)-Pd, CO molecules are bonded only in on-top positions of Pd atoms at 240 K; at 135 K, CO molecules are bonded in on-top positions of Pd atoms also for low coverage, and CO adsorbed both in on-top positions of Pd and Cu atoms for high coverage. For oxygen-contaminated Ni{001}c(2 x 2)-Al, CO molecules are bonded in on-top positions of Ni atoms and fourfold bridge positions between two Ni and two Al atoms, and the dissociation of CO has been observed at room temperature and low temperatures. The CO-dissociation rate is proportional to the degree of oxygen contamination on the surface.