The reactions of a potassium-containing bituminous coal briquette and the corresponding catalyst-free char with different NO/O-2 mixtures have been investigated at temperatures between 300 and 325 degrees C. The isothermal reactions have been followed by two techniques: thermogravimetry and gas chromatography + chemiluminescence analysis. A NO/NO2 mixture rich in NO2 results in a high carbon loss compared to that corresponding to the mixture poor in NO2. Despite that, NOx conversion is similar for both mixtures. The extra weight loss in the presence of a high concentration of NO2 is a consequence of NO2 reduction by carbon, producing NO and CO2 evolution.