IR spectroscopy study of NO adsorption and NO + O2 co-adsorption on Al2O3
Abstract
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.