CO OXIDATION BY ATOMICALLY ADSORBED OXYGEN ON AG(110) IN THE TEMPERATURE-RANGE 100-300 K

The catalytic CO oxidation reaction with atomically adsorbed oxygen on Ag(110) has been analyzed by means of molecular beam titration, molec ular beam relaxation (MBRS), qualitative LEED, and reactive thermal de sorption measurements (RTDS). The reaction has been observed and chara cterized in the temperature range 100-300 K. The CO2 formation rate de pends strongly on the reaction temperature. Additionally, the angular distribution of the desorbing CO2 is strongly peaked along the surface normal independent of the angle of incidence. Consequently, a Langmui r-Hinshelwood (LH) type model has to be applied for the whole reaction temperature range. The titration curves show two separate structures which are assigned to two reaction channels due to the existence of ki netically distinct oxygen species. These oxygen species are metastable in the sense that they are passivated in a thermally activated proces s which is proposed to be connected with the formation of the oxygen-i nduced reconstruction. The stabilized oxygen reacts again with CO at h igher temperatures (above 250 K). A reaction scheme is presented which consistently reproduces the experimental results and allows the deter mination of the kinetic parameters of the reaction.