Efficient dual acidic carbo-catalyst for one-pot conversion of carbohydrates to levulinic acid

Abstract

Levulinic acid (LA) is an important platform intermediate for several high value renewable bioproducts. One-pot synthesis of LA from carbohydrates is disadvantaged by the lack of proximity of the active sites required for sequential isomerization, dehydration and rehydration reactions. Herein, we report an efficient one-pot conversion of C₆ sugars to LA using a carbo-catalyst (ZrHyC), containing Lewis acidic zirconium and Brønsted acidic carboxyl and hydroxyl sites. The proximity of the two acid sites on a hydrothermally prepared carbon support makes the catalyst highly effective enabling a maximum 73% LA yield from glucose conversion. Fructose conversion achieved a higher LA yield (89%) because of a facile reaction without involving an isomerization step. The effects of solvents, the glucose to catalyst ratio, and the reaction time on glucose conversion and LA yield are systemically examined. Detailed characterization of the catalyst using FTIR, Raman spectroscopy, XPS, XRD, FESEM and NH₃-TPD techniques are presented to elucidate the presence of the two acid sites and zirconium in the +4 oxidation state.