Reexploring Size-Dependent Catalytic Performance under Same Metal Loadings and Identifying Real Active Species: From Single Atom, Cluster to Nanoparticle

Size-dependent catalysis is a classic and yet challenging issue in heterocatalysis because it is influenced by multiple factors such as varied metal loading and potential support effects. To the best of our knowledge, size-dependent catalytic research under the same metal loadings has rarely been reported. Herein, we designed and synthesized a series of unreducible SiO₂-supported Pt-based catalysts with the same metal loadings (0.3 wt %) but different particle sizes from single atom (SA), cluster to nanoparticle by combining amino group-assisted atomic layer deposition with the designed activation strategy. Their catalytic properties were probed in the archetypal CO oxidation reaction. The catalytic activity boosts prominently with increased particle size, which is well consistent with the directly observed gradual aggregation-activation process during the reaction process tracked by in situ STEM and isotope-labeled surface reaction and rationalized by theoretical calculations. The dynamic size transform and surface-confinement effect of porous SiO₂ also enable the Pt catalysts to achieve ultrahigh durability (> 2160 h) under the complete oxidation of CO, which is predominantly catalyzed by Pt nanoclusters/nanoparticles through the combined Mars-van Krevelen (66%) and Langmuir-Hinshelwood (34%) mechanisms. Similar phenomena were also found in catalytic hydrogenation and H₂O₂-involved oxidation reactions, i.e., SAs were poorly active, and nanoclusters/nanoparticles were clearly identified as the real active species. The dissociation energy of key small molecules (H₂/O₂/H₂O₂) is correlated with the particle size and catalytic activity, which can potentially act as a descriptor for the reaction activity. The present findings will afford deeper insights for deciphering the nature of size-dependent catalysis.