Beta zeolite: a universally applicable catalyst for the conversion of various types of saccharides into furfurals†
Carbohydrates, which consist of various types of saccharides, have been regarded as the potential alternative to fossil resources. However, the conversion of carbohydrates to chemical products generally requires energy- and time-consuming multiple processes. The present study shows that beta zeolites with both Lewis and Brønsted acid sites, prepared by facile calcination of the ammonium form of zeolite, promoted the direct conversion of various types of saccharides into furfurals. Beta zeolites with a large number of Lewis acid sites effectively promoted the direct conversion of glucose, other hexoses and even cellulose into 5-hydroxymethylfurfural (HMF). In the direct conversion of cellulose, the developed reaction system gave 42% yield of HMF; this value is significantly high for a heterogeneous reaction system. On the other hand, a beta zeolite with a small number of Lewis acid sites showed a better performance in the conversion of xylose into furfural than the one with a large number of Lewis acid sites. Suitable acid properties for the conversion of glucose and xylose are discussed in terms of reactivity of each substrate toward isomerization.