Direct catalytic conversion of carbohydrates to methyl levulinate: Synergy of solid Brønsted acid and Lewis acid

Abstract

Conversion of biomass derived carbohydrates to alkyl levulinates is an important process due to the wide application of alkyl levulinates as chemicals and biofuel additives. Efficient conversion of cheap and abundant glucose to alkyl levulinates over easily separated and regenerated solid catalyst is highly desirable. Here, the transformation of glucose to methyl levulinate (MLE) was studied over dual solid acid catalysts. The synergistic effect of solid Brønsted (B) acid and solid Lewis (L) acid was observed. A combined catalyst system consisting of both B acid and L acid was found to be more efficient for the production of MLE from glucose. 62% yield of MLE was given over the combined catalyst of SO42−/ZrO2 and Sn-Beta prepared by postsynthesis method at 170°C for 24h. The roles of L acid sites of SO42−/ZrO2 and Sn-Beta, and B acid sites of SO42−/ZrO2 were discussed in detail. Alternative biomass-derived carbohydrates also gave moderate to good yields of MLE. Recyclability studies indicated that the combined catalyst system can be reused without significant change in the yield of MLE, proving its easy recovery and thermal stability during regeneration.