Effects of the chemical states of N sites and mesoporosity of N-doped carbon supports on single-atom Ru catalysts during CO₂-to-formate conversion

This study explores the fabrication and characterization of mesoporous nitrogen-doped carbon replicas (MNCs) as Ru catalyst supports for CO₂ hydrogenation to formate. MNC supports with a cubic Ia3d-like structure were successfully synthesized from a KIT-6 template. The mesoporosity, N content, and N states in the MNCs differed according to the precursor type, which substantially influenced the stability of single-atom Ru catalysts during CO₂ conversion. In hydrogenation tests, the Ru/MNC prepared using acrylonitrile precursor (Ru/MNC-A) demonstrated the best stability, whereas the Ru/MNCs prepared using pyrrole and melamine exhibited low activity owing to Ru agglomeration and limited reactant diffusion, respectively. The excellent stability of Ru/MNC-A resulted from Ru migration and rearrangement, as evidenced by near edge X-ray absorption fine structure analyses. Ru/MNC-A and Ru/MNC-A-400 achieved an outstanding turnover number of 69,000 in CO₂ hydrogenation over 72 h. Remarkably, the Ru/MNC-A catalyst demonstrated exceptional stability, attaining a TON of 315,840 over 360 h.