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

It is shown that a bare ${\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3$ cluster can oxidize CO to form ${\mathrm{C}\mathrm{O}}_2$ and reduce NO to form ${\mathrm{N}}_2$ by undergoing compositional changes between ${\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_2$ and ${\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3$ 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 ${\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3$ 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 ${\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_2$ that now reduces NO via multiple oxidation and reduction steps that return the cluster to the oxidized ${\mathrm{F}\mathrm{e}}_2{\mathrm{O}}_3$ 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.