Developing Brønsted–Lewis acids bifunctionalized ionic liquids based heteropolyacid hybrid as high-efficient solid acids in esterification and biomass conversion

A class of Brønsted–Lewis acid bifunctionalized ionic liquids based heteropolyacid hybrid (BLA-ILs-HPA) solid acids were developed by combining the double sulfonic groups grafted, ionic liquids based heteropolyacid hybrid with Lewis acidic centers (M = Zn, Co, Fe, Ni, Cu). The prepared BLA-ILs-HPA show both Brønsted and Lewis acidic sites with extremely-high acid strength and enhanced stabilities, as determined by FT-IR, Py-IR, TG, XPS and 31 P solid state NMR results. BLA-ILs-HPA were successfully applied in esterification camphene with acetic acid to produce isobornyl acetate, and dehydration of glucose to produce 5-hydrozymethylfural. BLA-ILs-HPA show enhanced catalytic activities in comparison with various acid catalysts. The effects of reaction temperatures, initial reactant molar ratio, catalyst dosage, and reaction time were studied in detail. The optimal reaction conditions were obtained, and the experimental data was successfully correlated by a pseudohomogeneous (PH) reaction kinetic model in the temperature range of 313.15–333.15 K. The calculated values obtained by the reaction kinetic model were in good agreement with the experimental data. Moreover, as a heterogeneous reaction catalyst, BLA-ILs-HPA can be recovered by simple treatment. After six times cycling, the decreasing in the catalytic activity of BLA-ILs-HPA could not be observed significantly, suggesting their good reusability.