From Isolated Atoms to Ensembles: Precision-Tailored Active Sites on C 3 N 4 for Synergistic Phenylacetylene Carboxylation with CO 2

Regulating the dispersion of metal nanostructures is a central challenge in development of supported catalysts. The inevitable coarsening of these nanostructures during synthesis and catalytic reactions results in unwanted size evolutions driven by critical dynamic events such as redispersion and sintering. In this work, we propose a "shape-then-lock" strategy to achieve a stable and tailorable dispersion of supported Ag nanostructures over graphitic C3N4. By modulating the Ag coverage to balance competitive support-metal and metal-metal interactions within the Ag/C3N4 system, specific atomic dispersion systems can be predicted and engineered. This approach also allows for a crossover between supported Ag single atoms and monodispersed Ag nanoparticles as two extreme states. Utilizing this strategy, the optimal 2% Ag/C3N4 comprising tailored Ag single atoms and sub-nanometer clusters was achieved, which displayed a 94% yield in the carboxylation reaction of phenylacetylene with CO2 under mild conditions, significantly outperforming the single-dispersion system (65%) and the nanoparticle system (53%). Our approach not only facilitates the creation of monodisperse metal nanostructures for monofunctional catalysis but also enables the tailoring of specific multifunctional active sites that leverage cooperative effects among single atoms, clusters, and nanoparticles for tandem catalysis.