First-principles study of CO oxidation on bismuth-promoted Pt(111) surfaces

Vehicle emission control regulations necessitate the removal of carbon monoxide (CO) from engine exhausts via CO oxidation. Although bismuth (Bi)-promoted platinum (Pt) catalysts show improvement in CO oxidation performance over pure Pt, it is still not known whether Bi acts simply as a site blocker to reduce CO poisoning or whether it is an active participant in the catalytic reactions. In this study, we report density functional theory-based CO oxidation energetics and kinetics in the presence of different Bi dopant configurations. Adsorption energies for both CO and oxygen atoms are found to be reduced by Bi doping. Bi dopant also creates surface areas in its vicinity where CO adsorption is prohibited, whereas molecular oxygen dissociation is promoted. Significant reduction is shown for CO oxidation barriers on Bi-modified Pt(111) surfaces leading to exothermic CO2 formation. Our results elucidate that promoting Pt with Bi affects both the electronic properties of the catalyst and alters the Pt ensemble size available for elementary reactions within CO oxidation mechanism.