Operando X-ray absorption spectroscopy 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 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+2 O-2 clusters in contact with platinum nanoparticles; they coexist with spectator trivalent oxidic iron (Fe3+ ) and metallic iron (Fe0 ) partially alloyed with platinum. The 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 preferential carbon monoxide oxidation cycle.
Keywords: Heterogeneous Catalysis; Operando; Pt−Fe; Structure-Activity Relationships; X-Ray Absorption Spectroscopy.
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