Fully exposed palladium clusters mitigate catalyst poisoning during water contaminant reduction

Palladium-based catalysts hold great promise for water treatment applications but are often poisoned by sulfur species and natural organic matter (NOM). Here, we present a photochemical strategy to synthesize fully exposed Pd clusters through oxygen coordination to mitigate sulfur and NOM poisoning. These ultrasmall Pd clusters efficiently catalyze the hydrogenation of carbon–halogen bonds in sulfur-rich (50 µM) and NOM-rich (10 mg C/L) water matrices. Experimental and computational studies reveal that oxygen-coordinated Pd-Pd sites in fully exposed Pd clusters exhibit weaker sulfur and NOM adsorption at top and bridge sites, thereby mitigating catalyst poisoning. In contrast, conventional Pd nanoparticles possess predominantly metallic Pd sites that strongly bind poisoning species at hollow sites, resulting in rapid deactivation. These fully exposed clusters not only mitigate deactivation by sulfur and organic species, but also maintain high catalytic activity across a broad range of water contaminants and complex water matrices. This work presents a new design strategy for developing robust and selective hydrogenation catalysts for advanced water treatment applications.