This communication reports the NO reduction activity of potassium containing coal-briquettes prepared at different pyrolysis temperatures. For comparative purposes coal-chars prepared at the same temperatures have also been analyzed. NO reduction experiments were performed in a fix-bed flow reactor at atmospheric pressure using two types of experiment: (i) temperature programmed reaction in a NO/He mixture; and (ii) isothermal reactions at 600 degrees C. The reaction products were monitored in both cases, thus allowing detailed oxygen and nitrogen balances to be determined. It has to be pointed out that a previous in situ heat treatment in He before reaction is necessary for the low temperature activity of potassium containing coal-briquettes. For fresh briquettes, NO direct attack in addition to NO conversion by the catalytic action of potassium is observed at high temperatures. The NO direct attack, both in potassium containing samples and coal-chars, is clearly manifested by a nitrogen imbalance.