Alkali ion-promoted palladium subnanoclusters stabilized on porous alumina nanosheets with enhanced catalytic activity for benzene oxidation

Catalytic C−H bond activation is one of the backbones of the chemical industry. Supported metal subnanoclusters consisting of a few atoms have shown attractive properties for heterogeneous catalysis. However, the creation of such catalyst systems with high activity and excellent anti-sintering ability remains a grand challenge. Here, we report on alkali ion-promoted Pd subnanoclusters supported over defective γ-Al₂O₃ nanosheets, which display exceptional catalytic activity for C−H bond activation in the benzene oxidation reaction. The presence of Pd subnanoclusters is verified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy, X-ray absorption spectroscopy, and X-ray photoelectron spectroscopy. This catalyst shows excellent catalytic activity, with a turnover frequency of 280 h⁻¹ and yield of 98%, in benzene oxidation reaction to give phenol under mild conditions. Moreover, the introduction of alkali ion greatly retards the diffusion and migration of metal atoms when tested under high-temperature sintering conditions. Density functional theory (DFT) calculations reveal that the addition of alkali ion to Pd nanoclusters can significantly impact the catalyst’s structure and electronic properties, and eventually promote its activity and stability. This work sheds light on the facile and scalable synthesis of highly active and stable catalyst systems with alkali additives for industrially important reactions.