Cu–ZrO2 nanocomposite catalyst for selective hydrogenation of levulinic acid and its ester to γ-valerolactone

Abstract

Several copper based catalysts were prepared, characterized and evaluated for the hydrogenation of levulinic acid and its methyl ester. Among these, nanocomposites of Cu–ZrO₂ and Cu–Al₂O₃ quantitatively catalyzed the hydrogenation of levulinic acid and its methyl ester to give 90–100% selectivity to γ-valerolactone in methanol and water respectively. Both the Cu–ZrO₂ and Cu–Al₂O₃ nanocomposites were prepared by the co-precipitation method using mixed precursors under controlled conditions. XRD results showed that the main active phase of the reduced Cu–ZrO₂ catalyst was metallic copper and particle size was found to be of 10–14 nm by HRTEM. The active metal leaching was at a maximum for the Cu–Al₂O₃ catalyst in a water medium due to the formation of a copper–carboxylate complex that was blue in colour. Surprisingly, copper leaching was completely suppressed in the case of the Cu–ZrO₂ catalyst in methanol in spite of the substrate loading was increased from 5 to 20% w/w. The excellent recyclability of the Cu–ZrO₂ catalyst with complete LA conversion and >90% GVL selectivity makes it a sustainable process having a commercial potential.