Activity Enhancement of WO3-Promoted Ir/SiO2 Catalysts by High-Temperature Calcination for the Selective Reduction of NO with CO

Abstract The catalytic activity of WO3-promoted Ir/SiO2 for the selective reduction of NO with CO in the presence of excess O2 is strongly dependent on the catalyst calcination conditions in the preparation process. WO3/Ir/SiO2 catalyst prepared by air calcination showed higher activity than that prepared by H2 reduction. The activity of WO3/Ir/SiO2 catalyst prepared by air calcination was also found to increase with increasing calcination temperature up to 1073 K; however, a further increase in the temperature to 1173 K caused a decrease in the NO reduction activity, although very high selectivity was observed for this catalyst. The lack of a major difference in the apparent activation energy for NO reduction suggests that NO reduction occurs at the same reaction sites, irrespective of calcination temperature. On the other hand, the apparent activation energy for CO oxidation increased with increased calcination temperature, suggesting that the reaction sites for CO oxidation change according to calcination temperature. Catalyst characterizations revealed that iridium species interacting strongly with WO3 are preferentially created by high-temperature air calcination. A combination of partially reduced iridium species (IrO2−x) and WO3 (IrO2−x–WO3) was concluded to act as catalytically active sites of WO3/Ir/SiO2 for NO reduction.