High-Yield and High-Efficiency Conversion of HMF to Levulinic Acid in a Green and Facile Catalytic Process by a Dual-Function Bronsted-Lewis Acid HScCl4 Catalyst

Lignocellulosic biorefineries have received considerable attention for the purpose of producing high-value chemicals and materials. Levulinic acid (LA) is an important biomass-derived platform chemical that is produced from sugar-based biomass. Unfortunately, the catalysts reported thus far have shortcomings, such as expensive starting materials, complicated synthesis or purification operations, and a low LA yield under harsh reaction conditions. Herein, we develop a novel dual-functional catalyst, HScCl4, by combining Bronsted acid (HCl) and Lewis acid (ScCl3) sites. The as-prepared HScCl4 catalyst shows high efficiency and high selectivity for converting 5-hydroxymethylfurfural (HMF) to LA in a biphasic system consisting of methyl isobutyl ketone (MIBK) and water. The density functional theory (DFT) results show that the synergistic catalytic effect, originating from the Brensted and Lewis acidic sites of HScCl4, significantly decreases the energy barriers of reactants and intermediates, thus facilitating the conversion of HMF to LA. Moreover, the efficient separation of LA in the water-MIBK biphasic system by extracting LA to the MIBK phase minimizes the side reactions of LA and thus the formation of humins while significantly improving the LA yield. The conversion of HMF and the selectivity for LA are 100 and 95.6% at 120 degrees C for 35 min, respectively. The free energy (Delta G) and activation energy (E-a) of the reaction are -30 kcal mol(-1) and 13.7 kJ mol(-1), respectively. The developed process provides a green, sustainable, and efficient pathway to produce LA from biomass-derived HMF under mild conditions.

Automated summary

A novel dual-functional catalyst, HScCl4, was developed to efficiently convert 5-hydroxymethylfurfural (HMF) to levulinic acid (LA) with high yield and selectivity. The synergistic catalytic effect of the Brensted and Lewis acidic sites in HScCl4 significantly decreased energy barriers and facilitated the conversion process. Efficient separation of LA in the water-MIBK biphasic system minimized side reactions and improved the LA yield, providing a green and sustainable pathway to produce LA from biomass-derived HMF under mild conditions.