Crystalline-dependent valence dynamics of Pt on CaCO3 drives high activity in low-temperature propene combustion

Inverse Pt valence shift (Pt 4+ /Pt 2+ → Pt 0 ) on CaCO 3 during reaction. • Pt valence state depends on CaCO 3 crystal phase (vaterite, calcite, aragonite). • CaCO 3 facets tune surface Ca 2+ /CO 3 2- ratio, directing electron transfer to Pt. • Reaction mechanism shifts from Mars–van Krevelen to Langmuir–Hinshelwood pathway. • New paradigm of metal-support interaction on defect-free ionic solids. Unlike conventional metal oxide supports, the metal–support interactions (MSI) involving ionic crystals such as alkaline earth carbonates (e.g., CaCO 3 ) remain largely unexplored. Herein, we report an inverse transformation from PtO x to Pt 0 in the Pt/CaCO 3 system—a behavior distinctly different from that observed on conventional oxide supports like Pt/CeO 2 . Notably, this dynamic reduction from Pt 4+ to Pt 0 is highly crystalline-dependent: it is most pronounced on vaterite-supported Pt, while negligible on the more stable calcite and aragonite phases. XPS shows that the coordination of Pt with Ca–CO 3 ionic pairs correlates with CaCO 3 phase, governing electron transfer from the support to Pt. Such crystalline-dependent valence modulation enhances reactant co-adsorption and promotes low-temperature propene combustion, enabling synergistic MvK and L–H mechanisms, as corroborated by kinetic and isotopic data. This work introduces a new paradigm for tailoring electronic metal–support interactions (EMSI) on CaCO 3 –type ionic crystals. Download: Download high-res image (295KB) Download: Download full-size image