Abstract

In this work, Ni2P supported on SiO2 was investigated to evaluate the influence of particle size on the reductive amination of levulinic acid. The catalysts were prepared by incipient wetness impregnation and characterized by N2 adsorption-desorption, H2-TPD, XRD, CO-chemisorption, pyridine-FTIR, and XPS. Catalytic tests were carried out using aniline and 1-octylamine to produce the corresponding 5-methyl-1-substituted-2-pyrrolidones. The hydrogenation steps showed a clear volcano-type dependence on Ni2P particle size. The catalyst containing 5 wt % Ni (8.8 nm) exhibited the highest hydrogenation turnover frequencies (TOFs) for both amines. However, the highest hydrogenation rate for the formation of 5-methyl-1-phenyl-2-pyrrolidone was obtained with the 5 wt% Ni catalyst, whereas the maximum rate for 5-methyl-1-octyl-2-pyrrolidone was achieved with the 3 wt% Ni catalyst (4.9 nm). These differences are attributed to particle-size-dependent hydrogen adsorption: smaller particles bind hydrogen too weakly, while larger particles adsorb it too strongly. Optimal catalytic performance is therefore obtained at intermediate particle sizes, where hydrogen adsorption and surface reactivity are balanced.