CO Oxidation on Pd(111): A First-Principles-Based Kinetic Monte Carlo Study

CO oxidation on O-precovered Pd(111) surfaces exhibits remarkably different reactivities at different temperatures, which correlate with structural changes in the atomic O overlayer. Stoichiometric titration experiments by Nakai et al. (J. Chem. Phys. 2006, 124, 224712) show that although the p(2 x 2) ordered phase is inert, the (root 3 x root 3) and p(2 x 1) phases that form at 320 and 190 K, respectively, have different apparent activation energies and reaction orders with respect to O coverage. In this work, we perform first-principles-based kinetic Monte Carlo (kMC) simulations to understand the behavior of this catalytic system and shed light on the origin of the changes in reactivity. Accounting explicitly for lateral interactions among adsorbates and for their impact on the activation energies of the elementary processes, our simulations reproduce quantitatively the main features of the experimental measurements, and we show that the relative rates of CO adsorption and surface reaction are different as the temperature changes. We find that ordering of the adsorbate layer strongly depends on the strength of the lateral interactions but does not have a significant role on the catalytic properties of the system.