Electronic‐geometric synergy in sub‐nanometer iridium clusters enables efficient m ‐dinitrobenzene hydrogenation

Abstract Sub‐nanometer metal clusters provide an effective platform to bridge the gap between isolated atoms and nanoparticles in heterogeneous catalysis. Herein, we report the rational construction of Ir‐based catalysts with precisely controlled nuclearity on defect‐rich nanodiamond@graphene (ND@G), including single atoms (Ir 1 ‐ND@G), sub‐nanoclusters (Ir 6 ‐ND@G), and well‐defined nanoparticles (Ir N ‐ND@G), for the selective hydrogenation of m ‐dinitrobenzene. Advanced microscopy and spectroscopy confirm the precise structural evolution and electronic modulation of Ir species. Among them, Ir 6 ‐ND@G exhibits good catalytic performance, achieving complete conversion with >98.5% selectivity toward m ‐phenylenediamine under mild reaction conditions and high stability. Combined experimental studies and DFT calculations reveal that sub‐nanoclusters provide optimal ensemble sites for strong substrate adsorption, efficient H 2 activation, and facile product desorption while effectively suppressing undesired side reactions arising from partial hydrogenation and N–N coupling. This work demonstrates that sub‐nanometer Ir clusters effectively overcome the intrinsic activity–selectivity trade‐off and establishes a versatile strategy for designing high‐performance heterogeneous hydrogenation catalysts.