The heterogeneous reaction between soot and NO2 at elevated temperature

Two commercial soot samples are analysed by temperature programmed desorption mass spectroscopy (TPD-MS) in order to determine the functional groups at their surface. A systematic approach has been developed, which assures that all functional groups decomposing between 100 °C and 900 °C can be distinguished and assigned. For the understanding of the mechanism of the reaction between soot and NO₂ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and TPD-MS are applied. Both spectroscopic techniques monitor the formation of new species. The reaction with NO₂ results in the formation of an acidic functional group, which decomposes into CO₂ and NO at 140 °C. It is proven that NO₂ reacts directly with the carbon surface. Pre-existing functional groups do not interfere. From these results the reaction sequence has been concluded.