Nature and thermal stability of adsorbed intermediates formed during the reaction of diesel soot with nitrogen dioxide

Abstract The reactivity of a diesel exhaust soot sample towards 1000 ppm NO 2 /balance Ar was investigated at moderate temperature using thermogravimetric analysis (TGA), temperature-programmed desorption (TPD-MS) and diffuse reflectance infrared spectroscopy (DRIFTS) with the aim to evidence the nature and thermal stability of adsorbed intermediates formed during the reaction. In the range 25–200 °C, the reaction pathways are influenced by the temperature dependency of the reaction regimes. While weak adsorption of NO 2 prevails at temperatures under ca. 60 °C, it is found that associative and dissociative chemisorption occurs on the whole range of temperatures investigated, creating, respectively, nitrogenated (RNO x ) and oxygenated (RO x ) adsorbed intermediates on soot surface. DRIFTS and TPD experiments reveal that major surface species include on the one hand alkyl-nitrite and -nitrate esters adopting presumably a chelated or bidentate configuration on soot surface and on the other hand more stable acidic oxygenated surface complexes formed by reduction of NO 2 .