Synthesis, characterization and properties of Ce-modified S2O82−/ZnAl2O4 solid acid catalysts

Abstract

A new spinel solid acid catalyst of S₂O₈²⁻/ZnAl₂O₄-x wt% Ce was simply prepared by modifying S₂O₈²⁻/ZnAl₂O₄ with Ce for acid catalysis of acetic acid and n-butanol. The prepared catalysts were characterized by means of XRD, IR, TG, XPS, NH₃-TPD, SEM and N₂-physisorption. The experimental results showed S₂O₈²⁻/ZnAl₂O₄-x wt% Ce solid acid catalysts belonged to the spinel-type ZnAl₂O₄ structure. The addition of Ce played a key role in stabilizing the surface sulfur species and consequently increasing the acid strength of S₂O₈²⁻/ZnAl₂O₄-x wt% Ce. The appropriate modification of Ce was 4 wt% and S₂O₈²⁻/ZnAl₂O₄-4 wt% Ce catalyst had 95.9% esterification efficiency under the optimum reaction conditions. Compared with unmodified S₂O₈²⁻/ZnAl₂O₄ catalyst, S₂O₈²⁻/ZnAl₂O₄-4 wt% Ce solid acid catalyst showed much better reusability, which could remain above 80% esterification even after being used for six times. The loss of sulfur species on the surface of S₂O₈²⁻/ZnAl₂O₄-4 wt% Ce solid acid was one of the essential reasons for its deactivation during the acid catalyzed reaction.