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.