Regulation of Ni ⁰ and Ni ²⁺ Active Species for Solvent-Free Reductive Amination of Biomass-Derived Phenol with Ammonia

Synthesis of cyclohexylamine via reductive amination of biomass-derived phenol aligns with sustainable chemistry principles. However, the structure–activity relationships governing catalytic performance remain unexplored, which is crucial for regulating the product selectivity. In this work, an effective Ni3Al1Ox catalyst was developed for reductive amination of phenol to cyclohexylamine, achieving excellent yields. Both Ni0 and Ni2+ species are essential, and the best Ni2+/Ni0 ratio is 2.86. The optimal Ni2+/Ni0 ratio of the Ni3Al1Ox-600 catalyst is favorable for the adsorption of phenol and NH3 and the desorption of cyclohexylamine, which is key for achieving superior catalytic activity and selectivity.