Ammonia present in the product gas from coal gasification may increase NOx emissions from IGCC systems. A fixed bed reactor was used to study the effect of calcined limestone (CaO) on NH3 decomposition and reaction of NH3 and NO. Reactions at temperatures to 900 degrees C in helium and in gas compositions typical of air-blown gasifiers were studied. Although CaO enhanced ammonia decomposition in helium, reaction in the gasification atmosphere resulted in the loss of this catalytic activity. Increasing the total pressure further reduced the rate of NH3 decomposition. CaO enhanced conversion of NO to NH3 in gasification atmospheres.