Self-Stimulated NO Reduction and CO Oxidation by Iron Oxide Clusters

It is shown that a bare Fe₂O₃ cluster can oxidize CO to form CO₂ and reduce NO to form N₂ by undergoing compositional changes between Fe₂O₂ and Fe₂O₃ states. Investigations based on density functional theory reveal that the above reactions occur through an interesting sequence. An initial CO or NO adsorbed on the Fe₂O₃ weakens one of the O-Fe bonds to create a loosely attached O site. A subsequent CO gets oxidized by this O and transforms the cluster to a reduced Fe₂O₂ that now reduces NO via multiple oxidation and reduction steps that return the cluster to the oxidized Fe₂O₃ state. It is shown that the small size allows geometrical rearrangements that eliminate reaction barriers, allowing energetics and not barriers to be the primary motor for catalysis. Detailed reaction paths and the corresponding energetics are presented to illustrate the viability of the proposed mechanisms.