Resolving the Nanostructure of Carbon Nitride-Supported Single-Atom Catalysts.

Single-atom catalysts (SACs) are gathering significant attention in chemistry due to their unique properties, offering uniform active site distribution and enhanced selectivity. However, their precise structure often remains unclear, with multiple models proposed in the literature. Understanding the coordination environment of the active site at the atomic level is crucial for explaining catalytic activity. Here, a comprehensive study of SACs made of carbon nitride (CN) containing isolated nickel atoms is presented. Using a combination of synthesis techniques and characterization methods including Fourier-transform infrared spectroscopy, X-ray absorption spectroscopy (XAS), and density functional theory (DFT) calculations, the local environment of nickel active centers in CN-supported SACs is investigated. These results challenge conventional structural models and propose a new architecture that better aligns with current experimental evidence. This new structure serves as a foundational step toward a rational approach to catalyst development and can facilitate more precise design and application of these innovative catalysts.