NO₂ Adsorption on Ultrathin θ-Al₂O₃ Films:  Formation of Nitrite and Nitrate Species

Abstract

Interaction of NO2 with an ordered theta-Al2O3/NiAl(100) model catalyst surface was investigated using temperature programmed desorption (TPD) and X-ray photoelectron spectroscopy (XPS). The origin of the NO(x) uptake of the catalytic support (i.e., Al2O3) in a NO(x) storage catalyst is identified. Adsorbed NO2 is converted to strongly bound nitrites and nitrates that are stable on the model catalyst surface at temperatures as high as 300 and 650 K, respectively. The results show that alumina is not completely inert and may stabilize some form of NO(x) under certain catalytic conditions. The stability of the NO(x) formed by exposing the theta-Al2O3 model catalyst to NO2 adsorption increases in the order NO2 (physisorbed or N2O4) < NO2 (chemisorbed) < NO2- < NO3-.

Thermal and photochemical oxidation of self-assembled monolayers on alumina particles exposed to nitrogen dioxide

“…Chemisorption of nitrogen oxides on alumina is known to give a complex variety of adsorbed nitrite and nitrate species. 3,13,14,17,18,56,57 The amount of NO 2 that the substrate was exposed to was chosen to optimize the concentration of surface-adsorbed nitrite compared to nitrate. At higher NO 2 doses, nitrite is converted to nitrate via reaction (1): À1 are only observed in the presence of the organic, and track each other with time (i.e., their ratios remain constant), suggesting that they are due to organic products formed by reaction of surface-bound oxides of nitrogen with the C8= moiety.…”

The ozonolysis of primary aliphatic amines in fine particles

“…It should also be noted that there is a weak NO − 3 ion signal in the PERCI spectrum of 1-nitrohexane. This may be an experimental artifact arising from conversion of NO 2 to NO 3 on the metal surfaces (Ozensoy et al, 2005) in the ionization region of the mass spectrometer or from a disproportionation reaction (R1) (Sekimoto and Takayama, 2007):…”

“…There are several possible pathways that we believe exist in forming this ion including: a) disproportionation (R1); b) oxidation of NO 2 by ozone (R2); and c) conversion of NO 2 to NO − 3 via a surface reaction (Ozensoy et al, 2005) that occurs in the volatilization process. Reaction (R2) is likely the most important pathway to NO − 3 due to the concomitant increase in its ion signal intensity with increasing ozone exposure, as well as the very weak ion signal for NO 3 in the gas phase studies that suggest Reaction (R1) and surface processes are minor pathways.…”

Role of the Exposed Pt Active Sites and BaO2 Formation in NOx Storage Reduction Systems: A Model Catalyst Study on BaOx/Pt(111)

“…After an NO 2 exposure of 3600 L (P NO 2 = 10 À6 Torr  60 min, 1 L = 10 À6 Torr 3 s) at 323 K, a relatively strong peak becomes visible at 407.4 eV (Figure 4a, spectrum labeled with "+NO x "), which can be assigned to nitrate (NO 3 À ) species. 10,22 Nitrite (NO 2 À ) species that have a characteristic peak at ∼404 eV 23 are not readily visible in this spectrum (although a minor contribution from such species cannot be excluded). In the previous investigations 5,10 of NO 2 adsorption on BaO/Pt(111) system at 300 K, it has been shown that during the initial stages of NO 2 adsorption, nitrite formation precedes the formation of nitrates, whereas increasingly large exposures of NO 2 lead to the conversion of nitrite species into nitrates on the surface.…”