Tailoring Iridium Valence States on ZSM-5 for Enhanced Catalytic Performance in CO Selective Catalytic Reduction of NO under Oxygen-Enriched Environments.

Barium and iridium supported on Zeolite Socony Mobil-5 (ZSM-5) are efficient catalysts for the selective catalytic reduction of nitric oxide by carbon monoxide (CO-SCR), with enhanced cyclic stability. The introduction of Ba hindered the oxidation of metallic Ir active species and enabled Ir to maintain an active metallic state, thereby preventing a decrease in catalytic activity in the CO-SCR reaction. Moreover, the Ba modification increased the NO adsorption of the catalyst, further improving the catalytic activity. Owing to the better anti-oxidation ability of Ir0 in IrBa0.2/ZSM-5(27) than in Ir/ZSM-5(27), IrBa0.2/ZSM-5(27) showed better stability than Ir/ZSM-5(27). Considering that all samples in the present study were tested to simulate actual flue gases (such as sintering flue gas and coke oven flue gas), NH3 was introduced into the reaction system to serve as an extra reductant for NOx. The NOx conversion to N2 (77.1%) was substantially improved using the NH3-CO-SCR system. The proposed catalysts and reaction systems are promising alternatives for treating flue gas, which contains considerable amounts of NOx and CO in oxygen-enriched environments.