Selective reduction of NO with CO in the presence of O2 with Ir/WO3 catalysts: Influence of preparation variables on the catalytic performance

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 O2 (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 Ir loading of 0.5–1.0 wt.%. The good catalytic performance was achieved when the Ir precursors (IrOx) supported on WO3 were reduced under mild conditions by He at 400 °C or H2/He at a lower temperature of 130 °C. The catalysts were characterized by XRD, FTIR after CO adsorption, and H2-TPR. The characterization results show that the active sites are exposed zero-valent Ir species, in accordance with previous works using Ir on WO3 and other supports, and that the fraction of these active species is larger for a higher degree of Ir dispersion (smaller Ir particles). The preparation conditions for highly active Ir/WO3 catalysts were confirmed and possible reaction mechanisms were discussed.