Systematic optimization of the Ni-to-Mo ratio in bimetallic Ni–Mo₂C catalysts for efficient selective hydrogenation of levulinic acid to γ-valerolactone

Abstract

In this investigation, the optimization of Ni-to-Mo ratios in synergistic bimetallic Ni–Mo₂C catalysts was systematically investigated through a co-impregnation method, followed by the transformation of the calcined precursors into carbide structures via a carbothermal reduction process. The catalytic performance was evaluated for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL). Comprehensive physical and structural characterizations were carried out to elucidate the structure–activity relationships. In the designed Ni<inf>x</inf>Mo<inf>y</inf>C catalysts, a Ni to Mo ratio of 1.0: 1.0, corresponding to the Ni<inf>1.0</inf>Mo<inf>1.0</inf>C catalyst, exhibited the highest activity for hydrogenating LA into GVL. The superior performance of the Ni<inf>1.0</inf>Mo<inf>1.0</inf>C catalyst is attributed to the synergistic interfacial electronic interactions between the metallic Ni⁰ and Mo<inf>2</inf>C species, along with the presence of well-ordered carbon layer structures. Under optimized reaction conditions (160 °C, 20 bar H₂ pressure, 8 h reaction time, and 20 wt% catalyst loading), the Ni<inf>1.0</inf>Mo<inf>1.0</inf>C catalyst achieved complete LA conversion and a GVL yield of 97.4 %. This high performance is attributed to its small particle size, improved H<inf>2</inf> adsorption–desorption capacity, and the presence of appropriately distributed acidic sites. These findings highlight the competitive performance of Ni–Mo₂C catalysts for the efficient production of GVL from LA, offering promising applications in sustainable biorefinery processes.