Engineering Asymmetric Strain within C-Shaped CeO₂ Nanofibers for Stabilizing Sub-3 nm Pt Clusters against Sintering

Ultrafine noble metals have emerged as advanced nanocatalysts in modern society but still suffer from unavoidable sintering at temperatures above 250 °C (e.g., Pt). In this work, closely packed CeO₂ grains were confined elegantly in fibrous nanostructures and served as a porous support for stabilizing sub-3 nm Pt clusters. Through precisely manipulating the asymmetry of obtained nanofibers, uneven strain was induced within C-shaped CeO₂ nanofibers with tensile strain at the outer side and compressive strain at the inner side. As a result, the enriched oxygen vacancies significantly improved adhesion of Pt to CeO₂, thereby boosting the sinter-resistance of ultraclose sub-3 nm Pt clusters. Notably, no aggregation was observed even after exposure to humid air at 750 °C for 12 h, which is far beyond their Tammann temperature (sintering onset temperature, below 250 °C). In situ HAADF-STEM observation revealed a unique sintering mechanism, wherein Pt clusters initially migrate toward the grain boundaries with concentrated stain and undergo slight coalescence, followed by subsequent Ostwald ripening at higher temperatures. Moreover, the sinter-resistant Pt/C-shaped CeO₂ effectively catalyzed soot combustion (over 700 °C) in a durable manner. This work provides a new insight for developing sinter-resistant catalysts from the perspective of strain engineering within nano-oxides.