Catalysts Optimization of WO 3 ‐SiO 2 Supported Iridium for NOx Reduction by CO under Excess Oxygen Conditions

Abstract A series of Ir‐based catalysts were prepared by ultrasonic‐assisted equal‐volume impregnation to evaluate the catalytic performance of selective catalytic reduction of NOx by CO (CO‐SCR) with excess O 2 in simulated flue gas. We investigated the effects of different carrier, Ir loading, and composite carrier ratio (W/Si) on the CO‐SCR activities. The results showed that WO 3 and SiO 2 were effective carriers for the CO‐SCR reaction under oxygen‐rich conditions. Results of XRD and H 2 ‐TPR studies indicated that metal Ir strongly interacted with carrier WO 3 and SiO 2 , respectively, which improved the surface dispersion of active component Ir species and was conducive to the removal of NOx and CO. When W/Si molar ratio was 1/9 and Ir loading was 2 wt%, the Ir/WO 3 ‐SiO 2 catalyst reached 49 % NOx conversion and 76 % CO conversion at 225°C, while NO 2 yield was also only 5 ppm. The effects of O 2 , SO 2 , and H 2 O on the structure of Ir/WO 3 ‐SiO 2 were analyzed by XRD and XPS characterization methods. It was found that O 2 could oxidize Ir species to IrO 2 , thereby inhibiting NOx reduction. A low concentration of SO 2 can weaken the process of Ir oxidation, promote NOx reduction, and improve catalytic activity. H 2 O can reduce the NOx conversion rate and inhibit the CO‐SCR reaction, but the inhibition effect is reversible.