Mesoporous tantalum oxide as catalyst for dehydration of glucose to 5-hydroxymethylfurfural

• Mesoporous tantalum oxide is active in dehydration of glucose at 175 °C.
• The catalytic reaction is selective to 5-hydroxymethylfurfural (HMF).
• HMF is not rehydrated to produce levulinic acid.
• The catalyst can be fully recovered after calcination at 550 °C for 2 h.

Mesoporous tantalum oxide was prepared by acid hydrolysis of tantalum penta-ethoxide in the presence of a triblock co-polymer Pluronic L-121, a non-ionic surfactant, at room temperature and subsequent calcination at 550 °C for 6 h. This solid exhibits a suitable specific surface area (79 m2 g−1) and a high acidity (353 μmol NH3 g−1) with the presence of both Brönsted and Lewis acid sites, demonstrating to be active as solid acid catalyst in the dehydration of glucose to 5-hydroxymethylfurfural (HMF), in a biphasic water/methyl-iso-butyl ketone (MIBK) system. Thus, by using a glucose:catalyst weight ratio of 3:1, a glucose conversion of 69% and a HMF yield of 23% were achieved at 175 °C, and after only 90 min of reaction time. The catalytic process is selective toward HMF, which is preserved from ulterior hydration to levulinic acid. Fructose was also detected as by-product of glucose isomerisation with 14% of selectivity. The catalyst is very stable, since no leaching of tantalum species to the liquid phase was found; moreover, the catalytic performance of this acid solid is well recovered after calcination at 550 °C for 2 h.

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