Aluminum doped solid acid with suitable ratio of Brønsted and Lewis acid sites synthesized by electric-flocculation of phosphotungstic acid via hydrothermal treatment for producing 5-hydroxymethylfurfural from glucose

Novel solid acid catalyst PWAl-200 was synthesized by a new green method of electric-flocculation of phosphotungstic acid (PW) with aluminum as electrodes to transform glucose to 5-hydroxymethylfurfural (5-HMF). Through electric-flocculation, PW was deposited in the hydrated aluminum received from electrolysis. Then the obtained floc was treated by hydrothermal process to get solid acid. Characterization results showed that after electric-flocculation, the electron-withdrawing influence of terminal W O in the PW on hydrated aluminum formed Lewis (L) acid sites on these six-coordinated aluminum. The H + derived from PW could supply Brønsted (B) acid sites. In the further hydrothermal treatment, hydrated aluminum dehydrated to produce reformed six-coordinated aluminum. It was linked to heteropoly anions ligands through oxygen bridges, producing more L acid center. Besides, four-coordinated aluminum formed from the hydrated aluminum. The positive charge it produced increased L acid sites due to the strong effect of nearby tungsten species, further adjusting to a moderate ratio of Lewis/Brønsted (L/B) on solid acid for catalytic synthesis 5-HMF from glucose. The highest yield was 61.7% at 170 ℃ for 4 h and the catalyst could be recycled for four times and tend to stabilize.