Dealuminated Beta zeolite as effective bifunctional catalyst for direct transformation of glucose to 5-hydroxymethylfurfural

• Beta zeolites are effective catalysts in the transformation of glucose to HMF.
• Isomerization of glucose proceeds over Lewis acid sites generated by dealumination.
• The isomerization proceeds through intramolecular hydride transfer mechanism.
• Original Brønsted acid sites promote dehydration of fructose to HMF.
• The Beta zeolite catalyst can be regenerated by simple calcination.

To improve the catalytic performance of Beta zeolite in the direct transformation of glucose into 5-hydroxymethylfurfural (HMF), effects of calcination and steam treatment on the structure of Al atoms in the framework and acid properties of Beta zeolite were examined in detail. 27Al MAS NMR measurement and IR observation revealed that a part of Si–O–Al bonds in the framework were cleaved to form Al species out of the *BEA framework during the treatments and these species showed Lewis acidity. Especially, when the ammonium-type Beta was calcined over 700 °C or treated with steam (50 kPa in N2 balance) over 500 °C, the amount of Lewis acid sites was increased at the expense of Brønsted acid sites. Thus prepared Beta zeolite catalysts having a sufficient amount of Lewis acid sites were found to be effective bifunctional catalysts in synthesis of HMF from glucose; for example, Beta zeolite prepared by the calcination at 750 °C showed 55% selectivity to HMF at 78% conversion of glucose. We clarified the roles of Lewis and Brønsted acid sites on the Beta zeolite in the direct transformation of glucose to HMF. Furthermore, the reaction mechanism for the isomerization of glucose was investigated by means of isotope experiment using deuterated glucose. Finally, reusability of the Beta zeolite was also investigated.

Dealuminated Beta zeolites, which have two types of acid sites, are effective catalysts in the transformation of glucose to 5-hydroxymethylfurfural (HMF). Isomerization of glucose to fructose was promoted by Lewis acid sites through intramolecular hydride transfer and then fructose was dehydrated to HMF over Brønsted acid sites.Figure optionsDownload high-quality image (123 K)Download as PowerPoint slide