Production of 5‐Hydroxymethylfurfural from Fructose in Ionic Liquid Efficiently Catalyzed by Cr(III)‐Al2O3 Catalyst

A series of metal‐Al₂O₃ catalysts were prepared simply by the conventional impregnation with Al₂O₃ and metal chlorides, which were applied to the dehydration of fructose to 5‐hydroxymethylfurfural (HMF). An agreeable HMF yield of 93.1% was achieved from fructose at mild conditions (100°C and 40 min) when employing Cr(III)‐Al₂O₃ as catalyst in 1‐butyl‐3‐methylimidazolium chloride ([Bmim]Cl). The Cr(III)‐Al₂O₃ catalyst was characterized via XRD, DRS and Raman spectra and the results clarified the interaction between the Cr(III) and the alumina support. Meanwhile, the reaction solvents ([Bmim]Cl) collected after 1^st reaction run and 5^th reaction run were analyzed by ICP‐OES and LC‐ITMS and the results confirmed that no Cr(III) ion was dropped off from the alumina support during the fructose dehydration. Notably, Cr(III)‐Al₂O₃ catalyst had an excellent catalytic performance for glucose and sucrose and the HMF yields were reached to 73.7% and 84.1% at 120°C for 60 min, respectively. Furthermore, the system of Cr(III)‐Al₂O₃ and [Bmim]Cl exhibited a constant stability and activity at 100°C for 40 min and a favorable HMF yield was maintained after ten recycles.