Several Ir/WO3 catalysts were prepared, which were different in the loading of Ir (up to 10 wt.%) and in the pretreatment conditions, and used for the reduction of NO (500 ppm) with CO (3000 ppm) in the presence of excess O-2 (5%). SO2 (2 ppm), and H2O (1%). The rate of NO conversion per unit mole of Ir was found to be maximal at a small It loading of 0.5-1.0 wt.%. The good catalytic performance was achieved when the it precursors (IrOx) supported on WO3 Were reduced under mild conditions by He at 400 degrees C or H-2/He at a lower temperature of 130 degrees C. The catalysts were characterized by XRD, FTIR after CO adsorption, and H-2-TPR. The characterization results show that the active sites are exposed zero-valent Ir species, in accordance with previous works using it on WO3 and other supports, and that the fraction of these active species is larger for a higher degree of It dispersion (smaller It particles). The preparation conditions for highly active Ir/WO3 Catalysts were confirmed and possible reaction mechanisms were discussed. (C) 2008 Elsevier B.V. All rights reserved.