Efficient Reductive Amination of Furfural to a Primary Amine on a Pt/TiO2 Catalyst: A Manifestation of the Nanocluster Proximity Effect

Controlling both the hydrogenation performance and the activation of Schiff base intermediate in catalysts is crucial for attaining high slectivity toward primary amine in the reduction amination of furfural. However, it remains pending for Pt-based catalysts, on which the reduction amination reactions rarely generate primary amines so far. In this work, we developed a Pt/TiO₂ nanocluster (NC) catalyst with a size distribution independent of the reduction temperature and loading amount. The reductive amination performance was investigated by regulating the surface electronic state and the distance between Pt NCs, and the results, attractively, revealed that the catalyst with a lower loading amount exhibited a higher furfurylamine (FAM) yield. Further studies unraveled that the catalyst with a larger Pt NC proximity had more abundant effective adsorption sites for the key intermediate Schiff base, i.e., the surface Ti⁴⁺ sites adjacent to the Pt NC, promoting the transformation of the Schiff base. Meanwhile, reducing the surface density of Pt NCs helped control the intensity of hydrogen spillover, thereby inhibiting the occurrence of overhydrogenation reactions. Optimal activity for primary amine generation from furfural reductive amination was achieved with a Pt NC catalyst reduced at 500 °C and with a loading amount of only 0.1 wt %, resulting in a FAM yield exceeding 93% and a production rate of 297.9 g_FAM g_Pt h^–1. The reaction mechanism, involving the competitive relationship between NH₃ and H₂, was elucidated through kinetic studies and theoretical calculations. This work provides insights for the designation of catalysts with controllable hydrogenation activity and adsorption selectivity and contributes to the understanding of the mechanism of the reductive amination reaction.