Selective dehydration of glucose to 5-hydroxymethylfurfural on acidic mesoporous tantalum phosphate

• Mesoporous tantalum phosphate is active in dehydration of glucose at 170 °C.
• The catalytic reaction is very selective to 5-hydroxymethylfurfural (HMF).
• HMF is not hydrated to produce levulinic acid.
• No leaching of tantalum or phosphate is detected and catalysts can be reutilized.

Mesoporous tantalum phosphate was prepared from tantalum tartrate and ammonium phosphate monobasic in the presence of an ionic surfactant at room temperature, and subsequent calcined at 550 °C. This solid exhibits a high specific surface area (256 m2 g−1) and strong acidity (1.48 mmol NH3 g−1), and it has been successfully used as solid acid catalyst in the dehydration of glucose to 5-hydroxymethylfurfural (HMF) in a biphasic water/methyl isobutyl ketone medium. By using a glucose:catalyst weight ratio of 3:1, a glucose conversion of 56.3% and a HMF yield of 32.8% were achieved at 170 °C, and after only 1 h of reaction time. The reaction is very selective towards HMF, which is the unique product detected and moreover it is preserved from ulterior hydration to levulinic acid. Fructose was never found as by-product in the reaction. The catalyst is very stable under these experimental conditions, since no leaching of phosphorus or tantalum species to the liquid phase was found. The catalytic performance of this acid solid is well maintained after three catalytic cycles. The high catalytic activity of this mesoporous solid in the dehydration of glucose could be associated to its high acidity and the presence of both Brönsted and Lewis acid sites, which are maintained in water.

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