Self blocking of CO dissociation on a stepped ruthenium surface

The influence of steps on CO reactions has been studied on a (RU01154) single crystal with a step density of 4%. Based on temperature programmed desorption (TPD) and oxygen titration experiments as well as density functional theory (DFT) calculations, we show that the CO dissociation reaction only occurs on the steps. Under ultra high vacuum (UHV) conditions CO dissociates on the step, the oxygen reacts with CO to form CO₂ and the residual carbon blocks the step from further CO dissociation. This mechanism competes with the recombination of carbon and oxygen. At high CO pressures, we find step blocking no longer dominates the CO dissociation reaction to the same extent and further carbon uptake is observed. This self-poisoning effect is discussed in relation to similar studies of Ni(14 13 13) where such effects were not observed. We find the apparent dissociation energy on the step from experiments is in the range 1.3-1.5 eV, while the theoretical barrier for dissociation at low coverage is about 1.4 eV.