Revealing the Active Species for Aerobic Alcohol Oxidation by Using Uniform Supported Palladium Catalysts

The active species in supported metal catalysts are elusive to identify, and large quantities of inert species can cause significant waste. Herein, using a stoichiometrically precise synthetic method, we prepare atomically dispersed palladium–cerium oxide (Pd1/CeO2) and hexapalladium cluster–cerium oxide (Pd6/CeO2), as confirmed by spherical‐aberration‐corrected transmission electron microscopy and X‐ray absorption fine structure spectroscopy. For aerobic alcohol oxidation, Pd1/CeO2 shows extremely high catalytic activity with a TOF of 6739 h−1 and satisfactory selectivity (almost 100 % for benzaldehyde), while Pd6/CeO2 is inactive, indicating that the true active species are single Pd atoms. Theoretical simulations reveal that the bulkier Pd6 clusters hinder the interactions between hydroxy groups and the CeO2 surface, thus suppressing synergy of Pd‐Ce perimeter. Pd1 versus Pd6: Two different cerium oxide supported Pd catalysts with either Pd single atoms or Pd6 clusters are used for aerobic alcohol oxidation. Pd1/CeO2 shows high catalytic activity and satisfactory selectivity, but Pd6/CeO2 is inactive. Simulations reveal that the Pd6 clusters not only hinder the interactions between OH groups and the CeO2 surface, but also have a high barrier of H transfer from clusters to CeO2.