Toward a Silver-Alumina Model System for NOx Reduction Catalysis

The growth and morphology of Ag deposited on NiAl(110) and on oxidized NiAl(110) have been investigated by a combination of scanning tunneling microscopy (STM) and high-resolution core-level spectroscopy (HRCLS). While the STM measurements reveal complete wetting and a bilayer growth on clean NiAl(110), Ag nanoparticles with a minimum size of 5 nm were obtained on the oxidized NiAl(110). The difference in Ag growth mode on clean and oxidized NiAl(110) is supported by Ag 3d HRCLS. The binding energy for Ag on clean NiAl(110) is the same as for bulk Ag, while the Ag 3d peak for particles on oxidized NiAl(110) shifts toward the bulk binding energy with increasing size. The adsorption properties at 100 K of CO and NO on oxidized NiAl(110) and on Ag particles on oxidized NiAl(110) were also investigated by probing the C 1s and N 1s core levels. In the case of oxidized NiAl(110), neither CO nor NO adsorbs. In the case of Ag particles on oxidized NiAl(110), CO does not adsorb, but a component at 397 eV is observed in the N 1s level after NO exposures. This component is tentatively assigned to silver nitride, suggesting NO dissociation in the presence of Ag particles on oxidized NiAl(110).