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.

Atomically dispersed single atom catalysts represent an ideal means of converting less valuable organics into value-added chemicals of interest with high efficiency. Herein, we describe a facile synthetic approach to create defect-containing β-FeOOH doped with isolated palladium atoms that bond covalently to the nearby oxygen and iron atoms. The presence of singly dispersed palladium atoms is confirmed by spherical aberration correction electron microscopy and extended X-ray absorption fine structure measurements. This single palladium atom catalyst manifests outstanding catalytic efficiency (conversion: 99%; selectivity 99%; turnover frequency: 2,440 h⁻¹) in the selective hydrogenation of cinnamaldehyde to afford hydrocinnamaldehyde. Experimental measurements and density functional theory (DFT) calculations elucidate the high catalytic activity and the strong metal-support interaction stem from the unique coordination environment of the isolated palladium atoms. These findings may pave the way for the facile construction of single atom catalysts in a defect-mediated strategy for efficient organic transformations in heterogeneous catalysis.