Dehydration of sorbitol into isosorbide over silver-exchanged phosphotungstic acid catalysts

Transformation of renewable biomass into chemicals has attracted much attention recently. Efficient catalytic dehydration of biomass-derived sorbitol into isosorbide over solid acid catalysts under moderate reaction conditions is still a technical challenge. A series of silver-exchanged phosphotungstic acid catalysts were prepared by an ion-exchanged process, and dehydration of sorbitol into isosorbide was performed under solvent-free conditions. More than 99% conversion of sorbitol was obtained with 83% selectivity of isosorbide over Ag 1 H 2 PW catalyst at 140 °C within 1 h, which are comparable with that using a homogeneous phosphotungstic acid (HPW) catalyst. The silver-exchanged phosphotungstic acid catalysts were characterized by various techniques such as XRD, FT-IR, Raman, NH 3 -TPD and Py-IR to build a relationship between the catalytic activity and their natures. Ag 1 H 2 PW exhibited much higher activity for catalytic dehydration of sorbitol to isosorbide compared with Ag 2 H 1 PW and Ag 3 PW under the same reaction conditions, which was attributed to the stronger acidity and higher amount of Brönsted acid sites. Moreover, Ag 1 H 2 PW could be easily regenerated by 65% HNO 3 solutions and used repeatedly at least 3 times without obvious loss of catalytic activity.