Strong Ir–W interaction boosts CO-SCR denitration over supported Ir-based catalysts and influential mechanism of oxygen

Selective catalytic reduction of NO x with CO (CO-SCR) is deemed to be prospective technology instead of NH 3 -SCR denitration, while poor CO-SCR performance in the presence of excess O 2 profoundly hinders its further development. Herein, supported Ir catalysts with abundant active sites (Ir 0 and Ir–WO 3−x species) were prepared by ultrasonic-assisted impregnation, which achieved above 70 % NO x conversion and around 80 % N 2 selectivity at 250 °C in the presence of 5 % O 2. Also, NOx conversion maintained stable for more than 100 h due to the superior oxidation resistance of Ir-based catalysts that the ratio of Ir 0 /(Ir 0  + Ir 4+ ) only decreased by 1 % after the reaction. More importantly, a variety of characterization techniques including BET, XRD, XPS, H 2 -TPR, NO-TPD, and in situ DRIFTS measurements were employed. These results indicated that the highly dispersed Ir and WO 3 species had contributed to the strong Ir-W interaction, bringing about more exposed Ir 0 and Ir–WO 3−x active sites, and enhancing the adsorption and dissociation of NO. Meanwhile, the influential mechanism of O 2 on CO-SCR was studied. On the one hand, O 2 accelerated the adsorption of NO to generate more NO-adsorbed species (NO 3 –, NO 2 –, NO 2, and N 2 O 4 ), especially for monodentate nitrates, when the reaction temperature was below 250 °C and the oxygen concentration was below 5 %. They acted as active intermediates to react with CO to form N 2 and CO 2, which was beneficial to CO-SCR performance. On the other hand, as the reaction temperature increased, the absorption of NO was inhibited because active sites were occupied by oxygen, thus promoting CO oxidation with O 2 and inhibiting NO reduction with CO.