An Ir/WO3 catalyst for selective reduction of NO with CO in the presence of O2 and/or SO2 Original Research Article

The catalytic performance of Ir/WO3 catalyst has been studied in the reduction of NO with CO in the presence of O2 and/or SO2. The catalyst was active for the selective reduction of NO to N2 without foreign gases. The conversion of NO to N2 was further enhanced by the addition of a small amount of O2 while that to N2O was reduced. The N2 conversion went through a maximum, which depended on the composition of the reacting gaseous mixture (NO and CO). The catalyst was still active at higher O2 concentrations up to 5%, so this Ir/WO3 catalyst can be used effectively under lean-burn conditions. The presence of SO2 (100 ppm) caused a significant deactivation but this negative effect was completely removed by co-existing O2. The reaction mechanisms and the effects of co-existing O2 and SO2 gases are discussed on the bases of those reaction results, those of the reduction of NO2 instead of NO, and FTIR measurements of the catalysts after the reactions under various conditions. Possible reaction pathways are proposed, which depend on the concentration of O2 added in the reaction mixture.