Rate-Determining Steps in CO Oxidation on Pt Single Atom Sites on CeO₂ Surfaces

A recent experimental study on singly dispersed Pt atoms on CeO2 found that Pt atoms in the Ce substitution site show higher CO oxidation activity when found at the step edge than on the terrace. We present here the results of kinetic Monte Carlo simulations, based on reaction pathways from density functional theory-based calculations, to understand the rationale for the difference in the catalytic activity of the above-mentioned Pt single atom sites. Using the degree of rate control analysis, we find for CO oxidation reaction that O2 dissociation and desorption are the rate-determining steps for Pt single atom species on ceria terraces, while CO desorption is the primary rate-determining step for Pt single atom species at step edge sites, although O2 dissociation also becomes a rate-determining step at elevated temperatures. These results show that the main difference in CO oxidation activity on the two catalysts is their capacity for O2 dissociation, which correlates with the relative size of the energy barrier for the process on them. The kinetic Monte Carlo results are in qualitative agreement with experimental findings.