CO adsorption and dissociation on Ru(0001) at elevated pressures

We have investigated the adsorption and dissociation of CO on Ru(0001) surfaces at pressures from ultra-high vacuum up to 1 Torr and temperatures from 293 to 575 K using Ambient Pressure X-ray Photoelectron Spectroscopy (AP-XPS). At CO pressures above similar to 10(-6) Torr additional CO is adsorbed on the surface, leading to a CO coverage greater than the saturation coverage (0.66 ML) observed under UHV conditions. Binding energy shifts of the O 15 core level indicate that most of the additional adsorbed CO is located in bridge sites between two Ru atoms. At pressures above 10(-2) Torr the coverage of CO saturates at similar to 0.88 ML Isobaric measurements at 0.04 Torr CO indicate that the bridge bonded CO is stable up to a temperature of similar to 350 K and desorbs entirely by similar to 400 K. Additional CO desorbs over the temperature range of similar to 450 K to similar to 485 K. decreasing the CO coverage to similar to 0.58 ML. Above 520 K we observe the build-up of carbon on the surface which we attribute to the dissociation of CO. At 575 K and 0.04 Tort CO the equivalent of similar to 3.8 ML of carbon is present on the Ru(0001) surface. Potential mechanisms for the formation of this large amount of carbon on the surface will be discussed. (C) 2012 Elsevier B.V. All rights reserved.