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 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+2O−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. Operando X‐ray absorption spectroscopy revealed a linear correlation between the amount of oxidic Fe2+ and the ambient temperature activity of Pt−FeOx preferential carbon monoxide oxidation catalysts. The hydrogen prereduction temperature and pressure determines the amount of active Fe2+ sites for alumina‐ and silica‐supported Pt−Fe catalysts. Catalyst deactivation is linked with the oxidation of these sites.