Reduction of NO by CO on Unsupported Ir: Bridging the Materials Gap

Temperature programmed desorption (TPD) and density functional theory (DFT) are used to investigate adsorption sites and reaction of coadsorbed NO and CO on planar Ir(210) and faceted Ir(210) with tailored sizes of three-sided nanopyramids exposing (311), (311) and (110) faces. Both planar and faceted Ir(210) are highly active for reduction of NO by CO with high selectivity to N-2, which is accompanied by simultaneous oxidation of CO. Evidence is found for structure sensitivity in adsorption sites and reaction of coadsorbed NO and CO on faceted Ir(210) versus planar Ir(210). Strong interaction between NO and CO at high NO exposure and one-monolayer CO pre-coverage results in explosive evolution of N-2 and CO, on planar Ir(210) and size effects in reduction of NO by CO on faceted Ir(210) for average facet size ranging from 5 to 14 nm without change in facet structure.