Green and selective hydrogenation of aromatic diamines over the nanosheet Ru/g–C₃N₄–H₂ catalyst prepared by ultrasonic assisted impregnation-deposition method

In this study, nanosheet g–C₃N₄–H₂ was prepared by thermal exfoliation of bulk g-C₃N₄ under hydrogen. A series of Ru/g–C₃N₄–H₂ catalysts with Ru species supported on the nanosheet g–C₃N₄–H₂ were synthesized via ultrasonic assisted impregnation-deposition method. Ultrafine Ru nanoparticles (<2 nm) were highly dispersed on nanosheet g–C₃N₄–H₂. Strong interaction due to Ru-N_x coordination facilitated the uniform distribution of Ru species. Meanwhile, the involvement of surface basicity derived from abundant nitrogen sites was favourable for enhancing the selective hydrogenation performance of bi-benzene ring, i.e. almost complete 4,4′-diaminodiphenylmethane (MDA) conversion and >99% 4,4′-diaminodicyclohexylmethane selectivity, corresponding to a reaction activity of 35.7 mol_MDA mol_Ru⁻¹h⁻¹. Moreover, the reaction activity of catalyst in the fifth run was 36.5 mol_MDA mol_Ru⁻¹h⁻¹, which was comparable with that of the fresh one. The computational results showed that g-C₃N₄ as support was favorable for adsorption and dissociation of H₂ molecules. Moreover, the substrate scope can be successfully expanded to a variety of other aromatic diamines. Therefore, this work provides an efficient and green catalyst system for selective hydrogenation of aromatic diamines.