Catalytic valorization of biomass carbohydrates into levulinic acid/ester by using bifunctional catalysts

Methyl levulinate (ML) and levulinic acid (LA), important platform chemicals derived from biomass carbohydrates, are potential candidates for use as fuel additives and chemicals. In this work, bifunctional solid acid catalysts were prepared by impregnation via an environmentally friendly method and used for the conversion of glucose to ML and LA. In the conversion of glucose to levulinate, the isomeric conversion of glucose into fructose mainly utilized the Lewis acid sites properties exhibited by chromium, and the dehydration of fructose to 5-hydroxymethylfurfural and its degradation to levulinate mainly exploited the Brønsted acid sites properties exhibited by A15. The yield of ML and LA was 43.1 % and 1.2 %, respectively, and glucose was completely transformed into methanol within 2.0 h at 200 °C. The excellent activity of the best catalyst may be due to the sufficient total acidity and suitable ratio of the number of Lewis acid sites to that of Brønsted acid sites. The results for five catalysis cycles proved that the catalyst has good stability and reusability. In addition, the catalyst prepared was effective for the conversion of other carbohydrates, namely, sucrose, cellobiose, and 5-hydroxymethylfurfural to ML with yields of 83.3 %, 77.7 %, and 57.4 %, respectively.