The activity of potassium-containing coal pellets for NOx reduction in an oxygen-rich environment was investigated at 350 degreesC, during lifetime tests, until the sample was completely consumed. A complex reaction profile is exhibited by the samples, consisting of four different steps. As the potassium content increases, the selectivity towards NOx reduction, the amounts of NOx reduced per gram of sample (ash-free basis), and the maximum NOx conversion reached progressively increase. The highest potassium content sample can remove a considerable amount of NOx 3.1 g/g free-ash sample. (C) 2002 Elsevier Science B.V. All rights reserved.