Platinum-Iron(II) Oxide Sites Directly Responsible for Preferential Carbon Monoxide Oxidation at Ambient Temperature: An Operando X-ray Absorption Spectroscopy Study.

Operando X-ray absorption spectroscopy identified that the concentration of Fe 2+ species in the working state-of-the-art Pt-FeO x catalysts quantitatively correlates to their preferential carbon monoxide oxidation steady-state reaction rate at ambient temperature. Deactivation of such catalysts with time on stream originates from irreversible oxidation of active Fe 2+ sites. The active Fe 2+ species are presumably Fe +2 O -2 clusters in contact with platinum nanoparticles; they coexist with spectator trivalent oxidic iron (Fe 3+ ) and metallic iron (Fe 0 ) partially alloyed with platinum. The concentration of active sites and, therefore, the catalyst activity strongly depends on the pretreatment conditions. Fe 2+ is the resting state of the active sites in the preferential carbon monoxide oxidation cycle.