Dehydration Of Sorbitol Into Isosorbide Over Silver-exchanged Phosphotungstic Acid And WO₃/ZrO₂ 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 Ag₁H₂PW catalyst at 140 ^oC 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 Br?nsted acid sites.Moreover,Ag₁H₂PW could be easily regenerated by 65%HNO₃ solutions and used repeatedly at least 3times without obvious loss of catalytic activity.WO₃/ZrO₂ solid acid catalysts have attracted much attention recently,a series of WO₃/ZrO₂ catalysts which possessed different WO₃ amounts and calcined at different temperatures were prepared by coprecipitation and refluxing impregnation methods and dehydration of sorbitol into isosorbide was performed under solvent-free conditions.More than99%conversion of sorbitol was obtained with 73%selectivity of isosorbide at 200 ^oC within 3h over 15%WO₃/ZrO₂ catalyst which calcined at 800 ^oC.The WO₃/ZrO₂ solid acid catalysts were characterized by various techniques such as XRD,BET,Raman,NH₃-TPD and Py-IR to build a relationship between the catalytic activity and their natures.15%WO₃/ZrO₂ catalyst which calcined at 800 ^oC exhibited much higher activity for catalytic dehydration of sorbitol to isosorbide compared with other catalysts with different WO₃ amounts and different calcinations temperatures under the same reaction conditions,which was attributed to the stronger acidity and higher amount of Br?nsted acid sites.The acidity of WO₃/ZrO₂ catalysts can be affected by crystalline structures and surface area.