Reactivity of oxygen phases created by the high temperature oxidation of Ru(0001)

The carbon monoxide (CO) oxidation reaction, taking place over oxygen-rich Ru(0001) surfaces, has been used here as a simple probe of the reactivity of oxygen species formed by high temperature oxidation procedures. For surfaces oxidized at temperatures lower than 950 K a high reaction probability, within a range of 10(-2), has been found. The kinetics of CO, emission exhibit a fast and a long term component which reflects the contributions of the topmost and the subsurface oxygen phases, respectively. Both kinetic components are drastically reduced when working with surfaces resulting from the application of the same oxidation procedure but at temperatures above 950 K. For preparation temperatures above 1100 K the reaction probability is below the detection limit. In this temperature range, the oxygen phases show valence region ultraviolet photoelectron spectroscopy features characteristic of a regular RuO2 solid phase. Moreover, these non-reactive surfaces are marked by intense emission of RuO3, RuO4 and Ru2O molecular fragments as appearing in thermal desorption spectra in a temperature range 1000-1300 K. (C) 2000 Elsevier Science B.V. All rights reserved.