Precision Selenium Doping Unlocks Palladium Nanocluster for Efficient Chemoselective Hydrogenations

Supported subnanometric metal clusters have attracted widespread interest in heterogeneous catalysis owing to their high atom exposure and increased density of low-coordinated metals. However, these reactive metals are often in a highly charged state due to the strong metal-support interaction, leading to limited chemoselectivity toward multifunctional substrates and poor resistance to poisoning. This study demonstrates that the site-specific doping of trace selenium (Se) can sustain the metallic state of fully exposed palladium (Pd) nanoclusters, enabling chemoselective hydrogenation of halonitrobenzenes to haloanilines, an important yet highly challenging transformation. The precision Se-doped Pd nanoclusters outperform many reported noble-metal catalysts, achieving >99% selectivity at full conversion and a turnover frequency of 15,593 h^-1, together with excellent poison resistance and reusability. Mechanistic investigations reveal a semiquantitative correlation between the Pd⁰/Pd^δ+ ratio and haloaniline selectivity. Trace Se doping enriches electron density on Pd sites, enhancing H₂ activation while suppressing undesired hydrodehalogenation by modulating the adsorption and activation of haloanilines. This work not only establishes a versatile strategy to precisely tune the metallic state of metal clusters via Se doping but also provides insights for designing efficient catalysts that overcome support-induced electronic perturbations.