Theoretical Study on Nitrobenzene Hydrogenation by N-Doped Carbon-Supported Late Transition Metal Single-Atom Catalysts

A density functional theory (DFT) study was performed to investigate the activities of 12 late transition metal single-atom-supported nitrogen-doped carbon-based catalysts (M1-N4/C SACs) nitrobenzene hydrogenation. Three different dihydrogen (H2) dissociation mechanisms are proposed: homolytic cleavage at the metal (M) site, heterolytic cleavage at M–N sites, and heterolytic cleavage at M–N–C sites. The coadsorption of nitrobenzene (PhNO2) and H2 was proposed, and the effect of charge change of hydrogen atoms caused by the coverage of PhNO2 on the H2 dissociation activity was revealed. Six M1–N4/C SACs (M = Ru, Os, Fe, Ag, Ir, Rh) with a potentially high activity of H2 dissociation were screened. Then, the two crucial steps, H2 dissociation and the second N–O bond breaking (PhNOH* + H* → PhN* + H2O), were compared. The obtained results indicate that different M1–N4/C SACs might have different rate-determining steps for nitrobenzene hydrogenation and that Ru1–N4/C SAC could be one of the most promising catalysts with good catalytic activities for nitrobenzene hydrogenation.