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 o f oxygen species formed by high temperature oxidation procedures. For surfa ces 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 exhi bit a fast and a long term component which reflects the contributions of th e topmost and the subsurface oxygen phases, respectively. Both kinetic comp onents are drastically reduced when working with surfaces resulting from th e application of the same oxidation procedure but at temperatures above 950 K. For preparation temperatures above 1100 K the reaction probability is b elow the detection limit. In this temperature range, the oxygen phases show valence region ultraviolet photoelectron spectroscopy features characteris tic of a regular RuO2 solid phase. Moreover, these non-reactive surfaces ar e 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.