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.