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.