Catalysts Optimization of WO3-SiO2 Supported Iridium for NOx Reduction by CO under Excess Oxygen Conditions

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 WO3 and SiO2 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 WO3 and SiO2, 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/WO3-SiO2 catalyst reached 49 % NOx conversion and 76 % CO conversion at 225 degrees C, while NO2 yield was also only 5 ppm. The effects of O-2, SO2, and H2O on the structure of Ir/WO3-SiO2 were analyzed by XRD and XPS characterization methods. It was found that O-2 could oxidize Ir species to IrO2, thereby inhibiting NOx reduction. A low concentration of SO2 can weaken the process of Ir oxidation, promote NOx reduction, and improve catalytic activity. H2O can reduce the NOx conversion rate and inhibit the CO-SCR reaction, but the inhibition effect is reversible.