Catalytic hydrogenation of levulinic acid for the preparation of γ-valerolactone using CuAgZrO2-graphene nanocomposites

Hydrogenation of biomass-derived levulinic acid (LA) could produce a high value-added compound, gamma-valerolactone (GVL). However, metal leaching is a major issue in the efficient production of GVL from LA due to the acidity of LA. Some endeavors have tended to focus on the external factors of the catalysts for preventing metal leaching, such as reaction at high temperature and H-2 pressure or the esterification of LA with alcohols. Focusing on the catalyst itself, in this work, metal leaching was overcome by the selection of suitable catalyst compositions and preparation methods. The CuAgZrGO catalyst was synthesized by regulating the pH of the precipitation system to achieve a one-pot layered assembly of Zr4+, Cu2+, and Ag+ components on the graphene oxide (GO) surface at the atomic level. The catalyst without reduction pretreatment resulted in the complete conversion of LA and achieved approximately 100% yield of GVL, and metal leaching in the LA aqueous phase could be substantially prevented. Under mild reaction conditions, the catalyst exhibited good stability after four times of recycling in the aqueous phase. The positive-titration co-precipitation method controls the Ag more scattered on the surface of Cu and Zr precipitates, which makes CuAgZrGO a metal-leaching-resistant catalyst for aqueous-phase hydrogenation of LA.