Identifying Spatially Segregated Ir Sites Within ZSM‐5 for Enhanced Redox Cycle in NO<i>_x</i> Reduction by CO

Abstract Developing high‐performance Ir‐based catalysts for selective catalytic reduction of NO x by CO (CO‐SCR) under low temperatures remains challenging. This study presents an Ir‐based catalyst encapsulated in Zeolite Socony Mobil‐5 (Ir@ZSM‐5), with Ir species partially confined in micropores (Ir δ+ ) and partially aggregated on the surface (Ir 0 ), achieving ∼88% NO x conversion at 230 ° C in the presence of 5% O 2 and 100 ppm SO 2 . The confined Ir δ+ species exhibit enhanced stability and oxidation states, whereas surface‐aggregated Ir 0 species, with weaker oxygen coordination, remain in a metallic state. The dynamic equilibrium between Ir δ+ and Ir 0 significantly improves the balance of CO oxidation and NO reduction. O 2 promotes the oxidation of Ir 0 to Ir δ+ , whereas SO 2 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.