Chemisorption and Reaction of NO and N2O on Oxidized and Reduced Ceria Surfaces Studied by Soft X-ray Photoemission Spectroscopy and Desorption Spectroscopy
Journal of Catalysis 186 (1999) 296.
The chemisorption and reaction of NO and N2O on seria surfaces were studied by soft x-ray photoelectron spectroscopy (SXPS) and temperature programmed desorption spectroscopy (TPD). CeO2 thin films were grown in situ allowing control over the oxidation state of the cerium. The oxidation state was determined by Ce 3d, Ce 4d and valence band photoemission.
Following NO exposure at 100 K, various N-containing species were observed in the N 1s photoemission as shown at right. N2O forms on both the oxidized and the reduced surface. Nitrite, NO2-, also forms on the oxidized surface. This results from the adsorption of NO on the oxygen anions. These are the only species formed on the fully oxidized surface. Alternatively, NO- is formed on the reduced surface through the adsorption of NO on the Ce+3 cations. A small amount of NO- is formed on the oxidized surface, presumably at surface defects.
Different N-containing species are formed on the reduced surface depending on the adsorption temperature as shown at left. N2O and NO- are formed at 100 K. There is no N2O on the surface following adsorption at 145 K. At higher temperatures there are few molecular forms of N remaining on the surface. The NO dissociates, resulting in the oxidation of the substrate accompanied by N2 desorption and the formation of atomic and anionic N on the surface. At high NO exposures at 400 K, the oxygen from the NO dissociation displaces the N3- from the surface.
