Single-atom catalysts (SACs) have recently attracted broad attention in the catalysis field due to their maximized atom efficiency and unique catalytic properties. An atomic-level understanding of the interaction between the metal atoms and support is vital for developing stable and high-performance SACs. In this work, Pt₁ single atoms with loadings up to 4 wt.% were fabricated on ceria nanorods using the atomic layer deposition technique. To understand the Pt–O–Ce bond interfacial interactions, the stability of Pt₁ single atoms in the hydrogen reducing environment was extensively investigated by using in situ diffuse reflectance infrared Fourier transform spectroscopy CO chemisorption measurements. It was found that ceria defect sites, metal loadings and high-temperature calcination are effective ways to tune the stability of Pt₁ single atoms in the hydrogen environment. X-ray photoemission spectroscopy further showed that Pt₁ single atoms on ceria are dominantly at a +2 valence state at the defect and step edge sites, while those on terrace sites are at a +4 state. The above tailored stability and electronic properties of Pt₁ single atoms are found to be strongly correlated with the catalytic activity in the dry and water-mediated CO oxidation reactions.

Selective hydrogenation is an important industrial catalytic process in chemical upgrading, where Pd-based catalysts are widely used because of their high hydrogenation activities. However, poor selectivity and short catalyst lifetime because of heavy coke formation have been major concerns. In this work, atomically dispersed Pd atoms were successfully synthesized on graphitic carbon nitride (g-C₃N₄) using atomic layer deposition. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) confirmed the dominant presence of isolated Pd atoms without Pd nanoparticle (NP) formation. During selective hydrogenation of acetylene in excess ethylene, the g-C₃N₄-supported Pd NP catalysts had strikingly higher ethylene selectivities than the conventional Pd/Al₂O₃ and Pd/SiO₂ catalysts. In-situ X-ray photoemission spectroscopy revealed that the considerable charge transfer from the Pd NPs to g-C₃N₄ likely plays an important role in the catalytic performance enhancement. More impressively, the single-atom Pd₁/C₃N₄ catalyst exhibited both higher ethylene selectivity and higher coking resistance. Our work demonstrates that the single-atom Pd catalyst is a promising candidate for improving both selectivity and coking-resistance in hydrogenation reactions.