Water-induced efficient isomerization of glucose into fructose over the lithium loaded silicalite-1 catalyst at 50 °C

Abstract

Efficient H₂O-induced isomerization of glucose into fructose in 1 h at 50 °C over a novel lithium loaded silicalite-1 (Li/S-1) catalyst was demonstrated with 40.7% yield and 99.9% selectivity. The XRD, CO₂-TPD and ²⁹Si/⁷Li NMR results revealed the formation of the Si–O–Li group on the surface of S-1 zeolite, while the typical alkali-catalyzed reaction of glucose isomerization including the formation of enol intermediates and proton transfer at the C1 and C2 positions was revealed through the in situ FTIR and product liquid NMR analyses. In this catalytic process, the water-activated [Si–O–Li] group facilitates the polarization of α-carbon-linked carbonyl in glucose to result in the production of an enol intermediate, and subsequently the transfer and exchange of proton occurred to finally form fructose over the Li/S-1 catalyst.