Zeolite-promoted transformation of glucose into 5-hydroxymethylfurfural in ionic liquid

• Hβ-zeolite (Si/Al = 25) was very efficient for the conversion of glucose into HMF.
• The reaction kinetics was studied and determined to be first-order.
• Imidazolium cation and chloride anion of [BMIM]Cl had a synergistic effect.
• A plausible mechanism involving Lewis and Brønsted acid sites was proposed.
• Hβ-zeolite (Si/Al = 25) and [BMIM]Cl could be easily regenerated and recycled.

A variety of zeolite catalysts were investigated for the conversion of glucose into 5-hydroxymethylfurfural (HMF) in ionic liquid 1-butyl-3-methylimidazolium chloride ([BMIM]Cl), and the results revealed that Hβ-zeolite with a unique BEA structure and a moderate Si/Al ratio of 25 possessed the highest catalytic activity, which resulted in 50.3% HMF yield with 80.6% glucose conversion at a reaction temperature of 150 °C for only 50 min. In the presence of Hβ-zeolite (Si/Al = 25) and [BMIM]Cl, the reaction kinetics for the conversion of glucose into HMF was studied and determined to be in accordance with a first-order reaction rate equation, and the activation energy and pre-exponential factor were 97.4 kJ mol−1 and 2.2 × 1010 min−1, respectively. Moreover, a plausible mechanism involving the isomerization of glucose into fructose followed by the dehydration of fructose into HMF was proposed on the basis of the synergistic catalytic effect between Lewis acid sites and Brønsted acid sites of Hβ-zeolite. Hβ-zeolite (Si/Al = 25) could be easily regenerated via a simple calcination, and a similar HMF yield with the first reaction run was observed in the seventh reaction run. More importantly, Hβ-zeolite (Si/Al = 25) and [BMIM]Cl were also confirmed to be an excellent combination for the conversion of other carbohydrates such as fructose, sucrose, maltose, cellobiose, starch and cellulose into HMF.

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