(211c) Investigation of Structure Sensitivity for the CO Oxidation Chemistry On Pt and Au

The CO oxidation is a prototypic catalytic reaction for the study of structure sensitivity on metal surfaces. Yet, experimental results from different groups appear contradictory: studies on single crystal Pt, Ir, Rh and Pd surfaces have shown that CO oxidation is structure insensitive and attribute this effect on the surface being predominantly covered by CO, resulting in the rate being controlled by the CO desorption. Other studies, however, show that steps and terraces exhibit different activity, with the latter being much more active than the former, due to the preferential poisoning of the steps by CO. Thus, it still remains an open question whether the CO oxidation chemistry is structure sensitive and under what conditions.

In this study, we perform multiscale simulations that combine kinetic Monte Carlo with density functional theory based input on two different metals, namely Pt which exhibits strong binding for CO and O, and Au which exhibits weak binding for these species. We consider several surfaces with different ratios of step/terrace site numbers under various conditions, and investigate whether CO oxidation is structure sensitive. We show that the steps in the Au surfaces are much more active than the terraces. However, for Pt surfaces, poisoning effects by CO and/or O are important and may render the steps inactive, thereby resulting in the CO oxidation chemistry appearing structure insensitive under certain conditions.