Regulating the coordination environment of Co@C catalysts for selective hydrogenation of adiponitrile to hexamethylenediamine

Selective production of hexamethylenediamine (HMDA) by hydrogenation of adiponitrile (ADN) is a precondition to produce high-value added polyamides (e.g., nylon-66) and is still a great challenge by metal catalyst under alkali-free condition. Rational design of metal reactive center via modulated coordination endows a practical cure. We presented the significant role by forming Co-Nx coordinated sties in heterogeneous Co@C catalysts, which induced well crystallization of metallic Co phase with high-yield of HMDA under ultrafast intrinsic reaction rate (TOF of 2746 h−1). Characterizations suggested the simultaneous reduction of Coδ+ accompanied with carbon decomposition during pre-reduction, resulting in the strong Co-C interaction via Co-Nx coordination. Fine and stable Co particles around 5 nm were confined by mesoporous carbon layers with clear lattice distortion/expansion at Co-C interface. DFT calculation confirmed the electron modulation on the d-band center of Co with the strong affinity toward semi-hydrogenated ACN, facilitating the in-depth hydrogenation to HMDA. The Co coordinated states tuned by N was a fine regulator to modulate the spatial and electronic structure of Co active sites, positively correlating with the intrinsic activity. The Co@C-Z400 transformed ADN to HMDA with 90.7 % yield under sharply reduced activation energy of 37.9 kJ/mol.