IR spectroscopy study of NO adsorption and NO+O-2 co- adsorption on Al2O3

Adsorption of NO on Al2O3 leads to the formation of small amounts of surface nitro-nitrito (1461, 1318, 1228, 1220 and 1074 cm(-1)) and nitrato (1652 cm(-1)) complexes. Introduction of oxygen into the system causes oxidation of the NO2- compounds to nitrates (1628, 1591, 1565, 1298, 1259 and 1042 cm(-1)) whose concentration increases with time and with the oxygen amount. The nitrates obtained in this way are stable up to 723 K. They increase the Lewis acidity of Al3+ sites in the vicinity, as a result of which mononitrosyls of the type Al3+(NO3-)-NO(1938 cm(-1)) are formed. In addition, weakly bound N2O3 (1895, 1565, 1298 cm(-1)) and N2O4 (1752 cm(-1)) are obtained. Analysis of the spectra in the 2900-2400 cm(-1) region shows the presence of combination bands at 2883, 2624 and 2546-2526 cm(-1), which can be useful for the spectral identification of the surface anionic nitrogen-oxo species.