Unraveling the Synergistic Mechanism of Ir Species with Various Electron Densities over an Ir/ZSM-5 Catalyst Enables High-Efficiency NO Reduction by CO.

Selective catalytic reduction using CO as a reducing agent (CO-SCR) has exhibited its application potential in coal-fired, steel, and other industrial sectors. In comparison to NH 3 -SCR, CO-SCR can achieve synergistic control of CO and NO pollutants, making it a powerful denitrification technology that treats waste with waste. Unfortunately, the competitive adsorption of O 2 and NO on CO-SCR catalysts inhibits efficient conversion of NO x under O 2 -containing conditions. In this work, we obtained two Ir sites with different electron densities, Ir 1 single atoms in the oxidized Ir δ+ state and Ir 0 nanoparticles in the metallic state, by controlled pretreatment of the Ir/ZSM-5 catalyst with H 2 at 200 °C. The coexistence of Ir 1 single atoms and Ir 0 nanoparticles on ZSM-5 creates a synergistic effect, which facilitates the reduction of NO through CO in the presence of O 2 , following the Langmuir-Hinshelwood mechanism. The ONNO dimer is formed on the Ir 1 single atom sites and then spills over to the neighboring Ir 0 nanoparticles for subsequent reduction to N 2 by CO. Specifically, this tandem reaction enables 83% NO conversion and 100% CO conversion on an Ir-based catalyst at 250 °C under 3% O 2 .