A DRIFTS study of the heterogeneous reaction of NO2 with carbonaceous materials at elevated temperature

Commercial carbon black, spark generator soot, Diesel soot from passenger car and high-purity graphite were used for the investigation of the reaction of carbonaceous materials with NO2 applying diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The occurrence of infrared bands was analyzed as they were depending on the reaction temperature. The focus of interest was particularly on the conversion at an elevated temperature of 400 °C. The formation of oxidation products and the adsorption of NO2 on the surface of the samples were observed. Infrared bands could be attributed to C(O)OR, RNO2, and RONO as the main functionalities. The comparison of the results from the different samples revealed that different infrared signals appear when NO2 is adsorbed either on aliphatic or graphitic domains of soot. However, the formation of characteristic bands for an acidic functional group did not occur. This supports the assumption, made in a prior temperature programmed desorption mass spectroscopy (TPD-MS) study, that this group is a transition state.