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.