Pt-Fe+2O sites directly responsible for ambient temperature catalytic oxidation activity as discovered by operando XAS

Operando X-ray absorption spectroscopy (XAS) identified that the concentration of Fe2+ species in the working state-of-the-art Pt-FeOx catalysts quantitatively correlates to their preferential carbon monoxide oxidation (PROX) steady-state reaction rate at ambient temperature. Deactivation of such catalysts with time on stream originates from irreversible oxidation of active Fe2+ sites. The active Fe2+ species are presumably Fe+2O-2 clusters in contact with platinum nanoparticles; they coexist with spectator trivalent oxidic iron (Fe3+) and metallic iron (Fe0) partially alloyed with platinum. Concentration of active sites and, therefore, the catalyst activity strongly depends on the pretreatment conditions. Fe2+ is the resting state of the active sites in the PROX cycle.