Efficient conversion of glucose to 5-hydroxymethylfurfural by multi-functionalized γ-Al2O3 beads

CaO-doped gamma-Al2O3 beads were prepared by an alginate assisted sol-gel method, followed by grafting with alkyl groups and impregnation of NbCl5 to construct multi-functionalized gamma-Al2O3 beads for efficient catalytic conversion of glucose to 5-hydroxymethylfurfural (5-HMF). Doping with CaO improved the binding capacity of the catalyst with glucose and increased the Lewis acid amount. However, a high CaO content would cover the Lewis acid sites of gamma-Al2O3, resulting in a lower isomeric conversion of glucose to fructose. When the C-8-Ca(10%)-g-Al2O3 catalyst was loaded with Nb2O5, intermediate fructose was consumed rapidly resulting in complete conversion of glucose, which indicated that conversion of glucose to 5-HMF involved the isomeric conversion of glucose to fructose followed by dehydration of fructose to 5-HMF. This was necessary to balance hydrophilic isomerization reactions with restraining the rehydration of 5-HMF by hydrophobic modification. This is similar to the reaction in which a medium with a certain amount of water was beneficial for glucose isomerization. Under the synergistic effect of Lewis acid provided by gamma-Al2O3 and Bronsted acid offered by Nb2O5, C-8-Ca(10%)-gamma-Al2O3-Nb(3%), a glucose conversation rate of 100% and the highest yield of 5-HMF (68.4%) were achieved in the reaction medium with a dimethylsulfoxide/H2O (V/V) ratio of 4 : 1, a catalyst amount of 33 mg, a reaction temperature of 140 degrees C and a reaction time of 4 h.

Automated summary

By doping CaO, alkyl grafting and NbCl5 impregnation on γ-Al2O3 beads, an efficient catalyst was constructed for the conversion of glucose to 5-HMF. Under suitable reaction conditions, complete conversion of glucose and high yield of 5-HMF can be achieved.