Hydroxyl‑Mediated SO₂ Promotion Enables Efficient NO_x Reduction by CO over IrIn/Beta under Oxygen‑Rich Conditions

Developing high-performance Ir-based catalysts for the selective catalytic reduction of NO_x with CO (CO-SCR) under oxygen-rich conditions remains a formidable challenge. Here, we identify a hydroxyl-mediated reaction pathway over IrIn/Beta catalysts, termed the ammonium sulfate mechanism. Tailoring the support's Si/Al ratio modulates surface hydroxyls (Si-OH-Al), governing the rapid transformation of ammonium sulfate intermediates. Density functional theory calculations confirm that the formation of these intermediates is thermodynamically spontaneous and highly exothermic. These in situ-generated species rapidly decompose at 167 °C to release NH₃, triggering a built-in NH₃-SCR cycle. Notably, the IrIn/Beta-30 catalyst achieves 88% NO_x conversion under harsh simulated industrial conditions (15% O₂ and 200 ppm SO₂). This work establishes SO₂ as a contributing factor, providing a rational design strategy for robust denitration catalysts applicable to real-world industrial flue gas.