Synthesis of biofuel via levulinic acid esterification over porous solid acid consisting of tungstophosphoric acid and reduced graphene oxide

Abstract

Reduced graphene oxide (rGO) was synthesized by chemical reduction of graphene oxide with hydrazine hydrate and used as supports to prepare a series of H₃PW₁₂O₄₀ (HPW)-based porous solid acids for the first time. Esterification of levulinic acid with ethanol was used to investigate the catalytic properties of the resulting HPW/rGO catalysts. The results showed that the heterogeneous catalysts possessed a porous structure and that their textural characteristics and catalytic activities were influenced by the loading of HPW. Remarkably, they were efficient in the synthesis of ethyl levulinate, with the one with an HPW loading of 45 wt% exhibiting the best efficiency. The conversion of levulinic acid was as high as 96.9%. Meanwhile, the resulting HPW/rGO catalysts also have satisfactory durability. The conversion of levulinic acid still remains at about 53.1% after five cycles under the present conditions. Furthermore, the various catalytic reaction parameters, such as reaction time, ethanol-to-LA molar ratio, and the catalyst dosage, are optimized to maximize the conversion of levulinic acid over 45 wt% HPW/rGO catalysts.