Sticking probability of CO on an oxygen covered Pd{110}-surface under reaction conditions

The adsorption of carbon monoxide into an oxygen overlayer on a Pd(110) surface and its conversion to CO2 was studied by quantitative mass spectrometric methods and video recorded LEED. For temperatures with negligible desorption of CO (T≤420 K) the sticking probability of CO into the oxygen adsorbate is reduced by approximately 1/2 compared to a CO adsorbate on a clean Pd(110) surface of the same coverage. The evaluation reveals that each oxygen adatom effectively blocks more than ten sites for CO adsorption, which is explained by the influence of adsorbed oxygen on the transition probability of the CO precursor to the chemisorbed state. Initially due to a locally higher sticking probability CO is adsorbed at defects of the c(2×4) oxygen overlayer. After consumption of less ordered oxygen regions further reaction is restricted to the domain boundaries of the reactands and propagates preferably in an unidirectional fashion along the surface troughs with a constant turnover number until whole domains of oxygen have been consumed by the reaction