Chars prepared from coals treated with concentrated acids of HF and HCl to remove mineral matter were combusted under programmed temperature and isothermal conditions.The results showed that mineral matter in coal char played an important role in the conversion of char-N to NO. Alkali metals Na and K shifted the production of NO from char-N to a lower temperatures and inhibited NO emission. However

Ca and Fe increased the conversion of char-N to NO at a lower temperatures but decreased the release of NO at a higher temperatures

which implied the importance of catalytic condition and the complicated mechanism of NO formation and reduction. It was demonstrated that inert mineral matter in the char enhanced the conversion of char-N to NO. The net effect of mineral matter on NO emission level was combined effect of many components in mineral matter. It was also found that char-N conversion to NO increased with coal rank and NO emission increased with increasing temperature to maximum then decreased at a high temperature. The effect of mineral matter on NO emission depended on its relative catalytic activity in the oxidation of char-N to NO and reduction of NO by char.