Deactivation of Single-Atom Catalysts by Nanoparticles

Single-atom catalysts (SACs) represent a pinnacle of atomic efficiency and catalytic precision. Their remarkable activity and selectivity arise from isolated, low-coordinate metal centers that engage directly in bond-forming events. However, under realistic reaction conditions, SACs are far from static. Increasing evidence reveals that single atoms undergo dynamic evolution over the reaction time. In this perspective, we challenge the conventional dichotomy that views SACs and nanoparticles (NPs) as fundamentally distinct catalytic systems. We propose that NPs, rather than acting as parallel or cooperative catalysts, may function as catalytic poisonants for SACs by trapping active metal atoms. This transformation results in loss of activity, reduced selectivity, and degradation of the catalytic system. Drawing on mechanistic studies, thermodynamic data, and experimental observations across diverse reaction classes, including hydrogenation, oxidation, and cross-coupling, we show that the aggregation of SACs into NPs is not merely a side process but rather a limitation to their stability and utility. We further outline thermodynamic and kinetic strategies to suppress this deactivation pathway and propose design principles that elevate NP suppression from a synthetic challenge to a foundational criterion in catalyst development. This perspective reframes the SAC-NP relationship as a dynamic continuum and emphasizes the importance of stabilizing isolated active sites in next-generation catalytic technologies.