Developing high-performance Ir-based catalysts for selective catalytic reduction of NOx by CO(CO-SCR) under low temperatures remains challenging. This study presents an Ir-based catalyst encapsulated in ZSM-5 (Ir@ZSM-5), with Ir species partially confined in micropores (Irδ+) and partially aggregated on the surface (Ir0), achieving ~88% NOx conversion at 230 °C in the presence of 5% O2 and 100 ppm SO2. The confined Irδ+ species exhibit enhanced stability and oxidized states, while surface-aggregated Ir0 species, with weaker oxygen coordination, remain in a metallic state. The dynamic equilibrium between Irδ+ and Ir0 significantly improves the balance of CO oxidation and NO reduction. O2 promotes the oxidation of Ir0 to Irδ+, while SO2 facilitates the reverse, forming a reversible cycle that sustains catalytic efficiency. This work underscores the strategic interplay of Ir valence states and highlights a pathway for designing stable, high-performance Ir-based catalysts tailored for CO-SCR under complex reaction conditions.