Efficient catalytic conversion of glucose into 5-hydroxymethylfurfural by aluminum oxide in ionic liquid

Conversion of biomass-derived glucose to 5-hydroxymethylfurfural (HMF) is an important step for valorizing lignocellulosic biomass. In conventional reaction systems such as aqueous or water-organic solvent biphasic system, degradation of the formed HMF and other intermediates into undesired products is inevitable due to the presence of Brønsted acid, limiting HMF production efficiency. Here, we develop a novel reaction system consisting of heterogeneous catalyst with reduced Brønsted acidity and ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIMBr) to achieve the efficient conversion of high-concentration glucose to HMF. A series of Al-containing materials was synthesized and characterized by N2 adsorption-desorption, XRD, XPS, FIIR, Py-IR and CO2 TPD, among which the Al2O3-b-0.05 prepared by simple alkaline treatment exhibited high Lewis acidity and low Brønsted acidity. The Al2O3-b-0.05 in the medium of EMIMBr leaded to the highest HMF yield of 49.7% from high-concentration glucose (up to 10 wt%), as is more efficient than the heterogeneous EMIMCl/Al2O3-b-0.05 and homogeneous EMIMBr/AlCl3 system. This work provides a paradigm of improving HMF production efficiency via the combined use of heterogeneous Lewis acid catalyst and ionic liquid.