Harnessing the synergism between Ni particles and an Ni–ceria interface for efficient biomass reductive amination

Abstract

Catalytic reductive amination of 5-hydroxymethylfurfural (HMF) into primary amine has become a very promising upgrading route for cellulosic biomass. Ingenious integration of distinct catalytic centers on a single catalyst can synergistically drive the transformation of organic reactants and H₂ molecules, controlling product selectivity in this complex amination process. Herein, a ceria-supported Ni nanocatalyst with bifunctional Ni sites from the Ni particle surface and Ni–CeO₂ interface is reported. Regulating the size of Ni particles can gradually tune the interaction between Ni and ceria. Thus, the exposed amount of Ni⁰ active sites and the catalytic function of Ni at distinct locations can be finely modulated. The designed Ni catalyst achieved 100% yield of 5-aminomethyl-2-furanyl alcohol (AMF) and a high formation rate (10.6 g_AMF⁻¹ g_Ni⁻¹ h⁻¹) at 100 °C under a hypobaric H₂ pressure of only 2 bar. The investigation of the Ni size effect and reaction parameters revealed significant differences in product distribution, enabling a deeper understanding of the complex reaction path. It was disclosed that further selective transformations of reaction intermediates (i.e., imine and Schiff bases) are crucial for inhibiting byproducts (i.e., trimers and furfurine) and increasing the AMF yield. Physical characterizations and advanced chemisorption techniques revealed that the adsorption and activation of the Schiff base and H₂ occurred at the Ni surface and Ni–CeO₂ interface, respectively. The ammonolysis process involving NH₃ activation occurred on Ni²⁺ sites. The designed Ni/CeO₂ catalyst demonstrated good substrate scope for various bio-amine syntheses and exhibited stable reusability after suitable regeneration.