The effects of calcium and iron impregnated on coal chars as catalysts on NO-char reaction have been investigated under various atmospheres in a quartz fixed bed reactor. Temperature programmed reaction and isothermal reaction were used to determine the catalytic activities of calcium and iron in NO-char reaction. The results showed that the higher the pretreatment temperatures are, the lower is the catalytic activity of calcium, while the pretreatment temperatures had little effect on iron. Both calcium and iron promoted the NO-char reaction, but the catalytic activity of the latter was higher than that of the former. NO reduction by CO was strongly promoted by Fe and Ca impregnated on char, The presence of O-2 in the char-NO-Ca and char-NO-Fe or pure char-NO systems significantly promoted the NO reduction over carbon. Oxidation/reduction mechanisms were proposed for the NO reduction over char catalyzed by Ca and Fe. (C) 2002 Elsevier Science Ltd. All rights reserved.