Study on the mechanism of the reaction of NO2 with aluminium oxide

Abstract

In this study, the reaction of NO2 with aluminium oxide is examined. Aluminium oxide is an important component of NOx storage catalysts (NSC) that are used for the removal of nitrogen oxides from the exhaust gas of lean burn engines. Temperature-programmed desorption (TPD), diffuse reflectance infrared Fourier transformation spectroscopy (DRIFTS) and continuous analysis of gas-phase products are used in order to provide a better understanding of the reactions occurring during formation and thermal decomposition of surface species. For the adsorption of nitrogen dioxide, the experimental data suggest an ionic mechanism, in which molecularly adsorbed NO2 disproportionates into NO+ and NO3− species. The nitrosyl cation reacts with O2− surface species to form NO2− that is subsequently oxidized by NO2. This oxidation results in the production of NO3− and gaseous NO that leaves the surface. Thermal treatment of the surface species formed in NO2 reaction leads to the decomposition of the NO3− species between 380 and 550°C, resulting in the formation of NO2 and O2 in the molar ratio of 4 and reformation of the Al2O3 surface. At lower temperatures chemisorbed NO2 and adsorbed NO+ could desorb.