Sulfated Zirconia Catalysts for D-Sorbitol Cascade Cyclodehydration to Isosorbide: Impact of Zirconia Phase

Isosorbide is a widely touted intermediate for the production of biorenewable polymers and plastics, accessible through the aqueous phase cascade conversion of D-sorbitol to isosorbide via 1,4-sorbitan. However, existing routes to isosorbide typically employ mineral acids under forcing conditions, and hence alternative heterogeneously catalyzed processes are highly desirable. Aqueous phase D-sorbitol conversion was therefore investigated over families of sulfated zirconia (SZ) solid acid catalysts, with the effect of employing monoclinic, tetragonal ZrO2, or Zr(OH)4 as the parent support compared. The cascade proceeds via a stepwise dehydration to 1,4-sorbitan and subsequently isosorbide, with the latter favored over stronger acid sites. Monoclinic SZ exhibits superior activity to tetragonal SZ, reflecting a higher acid site density and pyrosulfate formation at lower SO42- loadings than over the other supports. Isosorbide selectivity at iso-conversion was proportional to acid site density, but independent of zirconia phase.