Electron acceptor NiO regulates the reduction of Cu supported on TiO2 for the efficient vapor-phase reductive amination of 1, 6-hexanediol

The conversion of alcohols recovered from biomass fuel into amine fine chemicals via C-O bond cleavage and C-N bond formation represents a highly desirable approach for amine compound preparation. Hexamethyleneimine (HMI) serves as a pivotal intermediate in the pharmaceutical, agrochemical, and insecticide industries. Industrial HMI production is currently constrained by limited scale and stringent process requirements. This study presents a novel strategy for the selective synthesis of HMI through vapor-phase one-step amination of 1,6-hexanediol (HDO) with ammonia, catalyzed by cost-effective NiO-decorated Cu/TiO₂. Under 1.5 MPa and 215 °C, the NiO-Cu/TiO₂ catalyst achieves complete HDO conversion, with a 98.5 % HMI selectivity and a 1.4-fold enhancement over copper active site alone. Comprehensive characterizations, including XRD, TEM, SEM-EDS, and XPS, elucidate the electronic interactions between copper and nickel oxide that nickel oxide incorporation effectively mitigates charge accumulation on copper, enhancing its hydrogenation capacity and facilitating the conversion of enamine intermediates to imines. DFT calculations reveal that dehydrogenation and hydrogenation processes are rate-determining steps of alcohol amination reaction. This catalyst system, leveraging inexpensive transition metals, holds promise for industrial-scale HMI production via efficient HDO amination.