Direct Amination of Biomass-based Furfuryl Alcohol and 5-(Aminomethyl)-2-furanmethanol with NH₃ over Hydrotalcite-derived Nickel Catalysts via the Hydrogen-borrowing Strategy

A series of hydrotalcite-derived nickel catalysts were synthesized and employed for the direct amination of biomass-based furfuryl alcohol with NH₃ via the hydrogen borrowing strategy. The effects of the Ni/Al molar ratio and calcination temperature of the NiAl hydrotalcite-like precursors on the performance of the Ni_xAl-CT catalyst were investigated. The systematic characterization showed that the synergistic catalysis of the metal and acid-base sites was of vital importance for the amination of alcohols. In particular, the Ni₂Al-600 catalyst with high amount of Ni⁰ sites (1.26 mmol g⁻¹) and suitable density of acid-base sites (0.71 mmol g⁻¹ and 1.10 mmol g⁻¹, respectively) exhibited the best dehydrogenation capability and therefore excellent catalytic activity. An 84.1 % yield of furfurylamine with complete conversion of furfuryl alcohol was obtained under the reaction conditions of 180 °C and 0.4 MPa NH₃ in 36 h. The presence of Ni₃N in the spent catalyst, confirmed by XRD, TEM and XPS characterizations, was demonstrated to be responsible for the deactivation of the Ni_xAl-CT catalyst. In addition, the Ni₂Al-600 catalyst exhibited satisfactory performance toward another important biomass-related transformation of 5-(aminomethyl)-2-furanmethanol to 2,5-bis(aminomethyl)furan, with a yield of 70.5 %.