Structure Sensitivity in Adsorption and Decomposition of NO on Ir

Abstract

The adsorption and decomposition of NO on planar Ir(210) and nanofaceted Ir(210) with tunable facet sizes (5−14 nm) have been studied by means of temperature programmed desorption (TPD), high-resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT). Evidence has been found for structure sensitivity in adsorption sites and thermal decomposition of NO on planar Ir(210) versus those on faceted Ir(210). Both planar and faceted Ir(210) surfaces are very active for NO decomposition with high selectivity to N2. Heating NO-saturated planar Ir(210) leads to desorption of large amounts of N2 and small amounts of NO together with traces of N2O. Annealing NO-saturated faceted Ir(210) also produces large amounts of N2 and small amounts of NO without the formation of N2O. Adsorption of NO at 300 K on both surfaces is predominantly molecular. On planar Ir(210) NO adsorbs on atop sites for the entire NO coverage range. On faceted Ir(210) that contains (110) and {311} faces, NO adsorbs on bridge and atop sites at low NO coverage while only on atop sites at high NO coverage. No evidence has been found for size effects in the thermal decomposition of NO over faceted Ir(210) for average facet size ranging from 5 to 14 nm.