Nanoconfinement of Pd Ensembles in Ceria’s Bridging Hydroxyl Nests for Enhanced C–H Bond Activation

Precise engineering of the metal-support interaction (MSI) is paramount for manipulating the geometric and electronic structures of supported metal catalysts, yet tailoring the local anchoring microenvironment at the atomic level remains a challenge. This study demonstrates how modulating the hydroxyl chemistry on CeO₂ can direct the MSI to stabilize distinct Pd species─from single atoms to subnanometric PdOx ensembles. We show that conventional terminal hydroxyl groups on CeO₂ favor the anchoring of Pd single atoms, whereas engineered bridging hydroxyl nests effectively confine undercoordinated PdOx clusters. This PdOx ensemble results in a moderate 4d orbital occupancy of Pd sites, which optimizes the σ-electron-acceptance and back-donation processes critical for C-H bond activation. Consequently, the PdOx ensemble catalyst achieves a dramatic decrease in methane combustion temperatures (T₅₀ and T₉₀ values are 340 and 402 °C, lowered by 175 and 226 °C, respectively) compared to the single-atom counterpart, alongside exceptional stability and water resistance under practical conditions. This work establishes the engineering of the support's hydroxyl microenvironment as a powerful strategy for designing highly efficient metal ensemble catalysts.