Cascade Upgrading of Biomass-Derived Levulinic Acid to γ-Valerolactone (GVL): A Biofuel Precursor over a Zr-Coordinated Hydrothermal Carbon Sphere via Catalytic Transfer Hydrogenation

Biomass-derived γ-valerolactone (GVL) is a high-quality liquid biofuel or value-added chemical and green solvent for various reactions commonly produced through the hydrogenation of levulinic acid (LA). The design of high-performance catalysts with superior catalytic universality is a particularly fascinating and important task, as it enables the easy and practical manufacture of GVL. Herein, a glucose-derived hydrothermal carbon (GHTC) sphere with plenty of oxygen-containing functional groups, serving as a cheap organic ligand, coordinated with Zr, was used as an efficient heterogeneous catalyst for a catalytic transfer hydrogenation reaction (CTH) in cascade conversion of LA into GVL. Among a series of different weight percentages of GHTC and metal precursor (ZrO(NO3)2), the sample with a 1:1 weight ratio shows the highest activity in LA hydrogenation. The selectivity for GVL formation was tuned by modulating Zr4+ with the formation of alkyl levulinate ester as an intermediate product. The conversion of LA into GVL is performed using the catalytic transfer hydrogenation method, where alcohol serves as both the solvent and a hydrogen donor during the reaction. The proposed reaction protocol is optimized by varying various reaction parameters, including catalyst amount, temperature, time, and different alcohols as hydrogen donors, to achieve the maximum yield and selectivity toward GVL formation. Under optimal conditions at 160 °C for 4 h, Zr-GHTC (1:1) achieved 99.58% conversion of LA and 98.71% yield of GVL using 2-propanol as a hydrogen donor with a turnover frequency (TOF) of 1.75 s–1. Moreover, the Zr-GHTC (1:1) catalyst demonstrated consistent performance across four successive cycles. Its straightforward, cost-effective, and easy synthesis of catalyst within a short time, along with its strong catalytic activity with high selectivity toward GVL formation under mild, inert atmospheric pressure conditions, offers a promising approach for the conversion of biomass-derived LA into value-added chemicals through a hydrogenation process that does not require molecular hydrogen. The synthesis of γ-valerolactone (GVL) from renewable biomass resources supports the principles of a circular economy and carbon neutrality, thereby providing a foundation for future research aimed at the sustainable production of environmentally benign solvents and fuel additives.