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

Abstract

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 Ag1H2PW 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, NH3-TPD and Py-IR to build a relationship between the catalytic activity and their natures. Ag1H2PW exhibited much higher activity for catalytic dehydration of sorbitol to isosorbide compared with Ag2H1PW and Ag3PW under the same reaction conditions, which was attributed to the stronger acidity and higher amount of Brönsted acid sites. Moreover, Ag1H2PW could be easily regenerated by 65% HNO3 solutions and used repeatedly at least 3 times without obvious loss of catalytic activity.