PNNL

Abstract

The NO;( storage properties of a BaO/?-Al[2]O[3]/NiAl(100) model system, with a BaO coverage of ~2 monolayer equivalent (MLE), was studied. X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) techniques were used to investigate NO[2] adsorption and reaction on the BaO/?-Al[2]O[3]/NiAl(100) surface. These results were compared with those of the ?-Al[2]O[3]/NiAl(100) support material, a thermally aged BaO/?-Al[2]O[3]/NiAl(100) model system, and a realistic BaO (20 wt%)/?-Al[2]O[3] high-surface area counterpart. At T > 300 K, adsorbed NO[2] is converted to nitrates on all of the surfaces studied. Nitrates residing on the alumina sites of the model catalyst surfaces are relatively weakly bound and typically desorb within 300-600 K, leading to NO(g) evolution; while nitrates associated with the baria sites are significantly more stable and desorb within 600-850 K, resulting in NO(g) or NO(g) + O[2](g) evolution. NO[x] uptake by the baria sites of the BaO/?-Al[2]O[3]/NiAl(100) model system was found to be as much as five-fold greater than that of the ?-Al[2]O[3]/NiAl(100) support material. Thermal aging of a BaO/0-Al[2]O[3]/NiAl(100) surface at 1100 K before NO[x] uptake experiments brings about a significant (>70%) reduction in the NO[x] storage capacity of the model catalyst surface.