Temperature-driven mechanistic transition in propylene oxidation over Pt/CeO₂ ensemble catalysts

Pt/CeO₂ ensemble catalysts are promising for propylene (C₃H₆) oxidation in vehicle exhaust, yet identifying the intrinsic active sites and understanding how the metal-support interface evolves at varying reaction temperatures remains contentious. Herein, we demonstrate that H₂-activated Pt/CeO₂ ensemble catalysts feature metallic Pt ensembles as intrinsic active sites, lowering the 50% conversion temperature by 120 °C after hydrogen activation. Various operando characterization techniques reveal an approximately 170 °C threshold temperature for the dynamic change of the reaction models. Meanwhile, kinetics and theoretical analysis illustrates that oxygen-facilitated dehydrogenation of sp³ C-H bonds is the rate-determining step. At low temperatures, both C₃H₆ and O₂ adsorb and activate on metallic Pt, without CeO₂ involvement. Once the temperature exceeds threshold, C₃H₆ fully covers Pt sites, while O₂ activates over Pt-O-Ce interfaces and participates in dehydrogenation. This study highlights the dynamic nature of oxygen activation, leading to distinct reaction temperature regimes during C₃H₆ oxidation.