The activity of potassium-containing bituminous coal briquettes for NOx reduction in an oxygen-rich environment has been investigated at temperatures of 300 and 350 degreesC. Two different procedures have been used for sample preparation: adding the alkali as the humic acid, or in a combined method (KOH + humic acid). The reaction has been followed by gas chromatography and chemiluminescence analysis. The main reaction products are N-2 and CO2. The potassium-containing coal briquettes improve the performance of the original char (without potassium) in the following aspects: (i) increasing the NOx conversion; (ii) decreasing the CO/CO2 ratio in the reaction products, and (iii) enhancing the selectivity toward the NOx reduction against combustion by oxygen. In this sense, a very interesting potassium-containing coal briquette has been prepared by using KOH + humic acid, as precursors. This sample exhibits a medium NOx conversion level, a high selectivity factor, and a low burnoff during an experiment carried out at 350 degreesC.