Scanning tunneling microscopy evidence for the Mars-van Krevelen type mechanism of low temperature CO oxidation on an FeO(1 1 1) film on Pt(1 1 1)

We provide experimental evidence that the low temperature CO oxidation reaction on an ultrathin FeO(1 1 1) film on Pt(1 1 1) proceeds through the Mars-van Krevelen type mechanism which includes the following steps: the FeO film is oxidized into an FeO2−x film with trilayer O–Fe–O structure; CO reacts with the weakly bound, topmost oxygen atoms, effectively reducing the FeO2−x surface to FeO-like; and the subsequent oxidation by O2 recovers the FeO2−x structure.

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► CO oxidation over FeO(1 1 1) thin films on Pt(1 1 1) is examined by STM.
► Sequential exposure to O2 and CO causes reversible transformations of the FeO film into the FeO2−x film.
► Strong evidence for the Mars-van Krevelen type mechanism of CO oxidation on these films.