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

Developing high-performance Ir-based catalysts for the selective catalytic reduction of NOx 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% NOx 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. Removing NOx from oxygen-rich industrial flue gas is difficult, especially with SO2 present. An IrIn/Beta catalyst turns SO2 into ammonium sulfate intermediates, promoting NOx high removal under harsh simulated industrial conditions.