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In order to understand the mechanism of C-NO reaction, the detailed material balance was established by analyzing all the gas species produced during the reaction with mass spectroscopy and gas chromatography. The amount of nitrogen-containing surface species was estimated in the temperature range between 600 and 950°C and with NO concentration of, mainly, 540 ppm. Then the effect of surface species on the reaction rate was examined. The step response experiments were carried out by switching the feed gas from 14 N 16 O to 15 N 18 O. The results reveal not only the reaction mechanism but also the depletion rate of surface nitrogen species during the experiment. N 2 formation rate was correlated with NO concentration and the amount of surface nitrogen species. It is concluded that N 2 is mainly formed by the first-order reaction between C(N) and NO.

The reaction between nitrogen oxides and carbon generates nitrogen-containing complexes on the carbon surface. The use of X-ray photoelectron spectroscopy allowed the characterization of these surface complexes. Five distinct structures have been distinguished, corresponding to nitrogen incorporated in five- and six-member ring as well as pyridine N-oxide and nitrate. Temperature has been found to be the determinant in the repartition of surface species. The reaction with NO−O2 at 600 °C has produced both pyrrolic and pyridinic nitrogens, while the reaction with NO at 950 °C mainly produced a pyridinic one. Quaternary nitrogen increased upon the heat treatment in He at 950 °C after the char was reacted with NO−O2 at 600 °C.

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