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

Millimeter size gamma-Al2O3 beads were prepared by alginate assisted sol-gel method and grafting organic groups with propyl sulfonic acid and alkyl groups as functionalized gamma-Al2O3 bead catalysts for fructose dehydration to 5-hydroxymethylfurfural (5-HMF). Experiment results showed that the porous structure of gamma-Al2O3 beads was favorable to the loading and dispersion of active components, and had an obvious effect on the properties of the catalyst. The lower calcination temperature of gamma-Al2O3 beads increased the specific surface area, the hydrophobicity and the activity of catalysts. Competition between the reaction of alkyl groups and -SH groups with surface hydroxyl during the preparation process of the catalyst influenced greatly the acid site densities, hydrophobic properties and activity of the catalyst. With an increase in the alkyl group chain, the hydrophobicity of catalysts increased obviously and the activity of the catalyst was enhanced. The most hydrophobic catalyst C-16-SO3H-gamma-Al2O3-650 degrees C exhibited the highest yield of 5-HMF (84%) under the following reaction conditions: reaction medium of dimethylsulfoxide/H2O (V/V, 4:1), catalyst amount of 30 mg, temperature of 110 degrees C and reaction time of 4 hr.