Y-Shaped FeN₃ Active Sites on Graphyne for Catalytic CO Oxidation: A First-Principles Study

The CO catalytic oxidation process on the surface of Fe-N₃ co-doped graphyne was systematically investigated using first-principles calculations combined with the climbing-image nudged elastic band (CI-NEB) method. The Y-shaped FeN₃ active sites on the graphyne surface were constructed by forming stable N-C covalent bonds between three N atoms and their adjacent C atoms and by establishing coordination between the transition metal Fe atom and three N atoms. CO and O₂ molecules were chemisorbed on the doped surface through the formation of Fe-C and Fe-O bonds with the FeN₃ active sites, with the C1 configuration surface exhibiting a stronger adsorption capacity toward the gas molecules. Comparative analysis of the kinetic behaviors of CO catalytic oxidation under three distinct reaction mechanisms, Eley-Rideal (ER), Langmuir-Hinshelwood (LH), and termolecular Eley-Rideal (TER), revealed that CO molecules preferentially undergo oxidation along the ER1 pathway on the FeN₃-doped graphyne surface. The rate-determining step (RDS) energy barriers are 0.409 and 0.002 eV, respectively, with substantial heat released during the reaction process. Following the desorption of CO₂ via the ER1 pathway, the remaining O atom on the doped surface can further react with another CO molecule at low energy barriers (0.066 eV for C1 and 0.016 eV for C2) to form a second CO₂ molecule, indicating that the catalytic activity of the doped substrate can be fully restored. Owing to the moderate adsorption strength for CO molecules on the C2 surface with an adsorption energy of -1.108 eV, the catalytic oxidation process along the TER pathway presents distinct advantages over several noble-metal catalysts and transition-metal-doped two-dimensional material catalysts. The energy barrier of the RDS is only 0.609 eV, and the reaction proceeds with continuous heat release. Therefore, modifying the graphyne surface via Fe-N₃ coordination doping may provide a new perspective for the design of graphyne-based single-atom catalysts.