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 NH₃-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 O₂ and NO on CO-SCR catalysts inhibits efficient conversion of NO_x under O₂-containing conditions. In this work, we obtained two Ir sites with different electron densities, Ir₁ single atoms in the oxidized Ir^δ+ state and Ir⁰ nanoparticles in the metallic state, by controlled pretreatment of the Ir/ZSM-5 catalyst with H₂ at 200 °C. The coexistence of Ir₁ single atoms and Ir⁰ nanoparticles on ZSM-5 creates a synergistic effect, which facilitates the reduction of NO through CO in the presence of O₂, following the Langmuir–Hinshelwood mechanism. The ONNO dimer is formed on the Ir₁ single atom sites and then spills over to the neighboring Ir⁰ nanoparticles for subsequent reduction to N₂ by CO. Specifically, this tandem reaction enables 83% NO conversion and 100% CO conversion on an Ir-based catalyst at 250 °C under 3% O₂.