STUDY OF CO OXIDATION OVER RU(0001) AT HIGH GAS-PRESSURES

Experiments performed at high gas partial pressures have demonstrated that the kinetics of the CO oxidation reaction over Ru(0001) are diffe rent and somewhat anomalous compared to those over other transition me tal surfaces and, in particular, that the turnover rate is exceptional ly high. In order to gain insight into the underlying reasons for this behavior, we performed density functional theory calculations using t he generalized gradient approximation for the exchange-correlation fun ctional. We find that the high rate is due to a weakly, but neverthele ss well bound, (1 x 1) oxygen adsorbate layer which may form for high O-2 pressures but not under usual ultra-high vacuum conditions. The ca lculations indicate that reaction to CO2 occurs both via scattering of gas-phase CO molecules and by CO molecules weakly adsorbing at vacanc ies in the oxygen adlayer, where the latter mechanism dominates the ra te.