Adlayer inhomogeneity without lateral interactions: Rationalizing correlation effects in CO oxidation at RuO2(110) with first-principles kinetic Monte Carlo

Abstract

Microkinetic modeling of surface chemical reactions still relies heavily on the mean-field based rate equation approach. This approach is expected to be most accurate for systems without appreciable lateral interactions among the adsorbed chemicals, and there in particular for the uniform adlayers resulting in poisoned regimes with predominant coverage of one species. Using first-principles kinetic Monte Carlo simulations and the CO oxidation at RuO(2)(110) as a showcase, we demonstrate that even in this limit mean-field rate equations fail to predict the catalytic activity by orders of magnitude. This deficiency is traced back to the inability to account for the vacancy pair formation that is kinetically driven by the ongoing reactions.

Transitions between strongly correlated and random steady-states for catalytic CO-oxidation on surfaces at high-pressure

“…It is clear from our above analysis of various truncation approximations, and from the earlier work of Matera et al, 25 that an accurate treatment of the empty site statistics is the key to a reliable description of reactivity. Thus, we are motivated to improve on the descriptions in Sec.…”

“…The dominant processes are singlesite CO adsorption and desorption, thus producing a random CO adlayer with coverage determined by the CO adsorptiondesorption balance. This simple behavior, for which MF kinetics naturally applies, was noted by Reuter et al in their modeling, 24,25 and will not be the focus of our analysis. We find a fairly sudden crossover through a peak in the TOF to a Regime II for lower p CO below about 0.1 which corresponds to a near Ocovered surface with strong spatial correlations.…”

“…A key observation by Matera, Meskine, and K. Reuter (MMR) 25 for the analogous regime in their model of CO-oxidation on RuO 2 (110) is that strong correlations in the adlayer are associated with the feature that empty sites are mainly created in NN pairs. The dominance of vacancy pairs, which implies that [E|E] = 1/(2d), was attributed to their creation by dimer desorption and CO + O reaction.…”

“…(We will see that these correlations are similar to those in the reaction model for low p CO . 25 ) For dimension d = 1 or 2, this implies that…”

“…16 However, in the current study, we instead focus on elucidating distinct generic regimes of behavior and the associated spatial correlations in the mixed reactant adlayer. Of specific interest is the observation by Reuter and coworkers 24,25 of a transition from primarily CO-populated surface for higher COpartial pressure, p CO , with a random distribution of CO (or of isolated vacancies) to a near O-covered surface for lower p CO but with strong correlations in the distribution of O adatoms (or of vacancies). These correlations invalidate a treatment based on MF kinetics.…”