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.