5-Hydroxymethylfurfural (HMF) is a key versatile building block in the valorization of lignocellulosic biomass. A series of metal oxides and metal phosphates was investigated as heterogeneous catalyst to convert glucose into HMF in the ionic liquid 1-ethyl-3-methylimidazolium bromide (EMIMBr). The heterogeneous conversion of a high-concentration glucose (up to 20 wt%) into HMF in ionic liquid has been achieved for the first time. Tin phosphate in the medium could afford a high HMF yield (58.3%) comparable to the best results obtained with the most effective homogeneous catalysts. To elucidate the reaction mechanism, SnO2, sSnPO and SnPO were characterized by N2 adsorption-desorption, XRD, TEM, XPS, UV–vis, FIIR, Py-IR and CD3CN-IR. It was found that tetra-coordinated Sn4+ sites from tin phosphate are responsible for the isomerization of glucose into fructose, while the conversion of fructose into HMF is mainly catalyzed by the ionic liquid EMIMBr. The excellent catalytic performance was attributed to the synergistic effect between SnPO and EMIMBr.
- Heterogeneous catalysis
- Ionic liquid