Synthesis, characterization and properties of Ce-modified S 2 O 8 2− /ZnAl 2 O 4 solid acid catalysts

A new spinel solid acid catalyst of S 2 O 8 2− /ZnAl 2 O 4 - x wt% Ce was simply prepared by modifying S 2 O 8 2− /ZnAl 2 O 4 with Ce for acid catalysis of acetic acid and n -butanol. The prepared catalysts were characterized by means of XRD, IR, TG, XPS, NH 3 -TPD, SEM and N 2 -physisorption. The experimental results showed S 2 O 8 2− /ZnAl 2 O 4 - x wt% Ce solid acid catalysts belonged to the spinel-type ZnAl 2 O 4 structure. The addition of Ce played a key role in stabilizing the surface sulfur species and consequently increasing the acid strength of S 2 O 8 2− /ZnAl 2 O 4 - x wt% Ce. The appropriate modification of Ce was 4 wt% and S 2 O 8 2− /ZnAl 2 O 4 -4 wt% Ce catalyst had 95.9% esterification efficiency under the optimum reaction conditions. Compared with unmodified S 2 O 8 2− /ZnAl 2 O 4 catalyst, S 2 O 8 2− /ZnAl 2 O 4 -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 S 2 O 8 2− /ZnAl 2 O 4 -4 wt% Ce solid acid was one of the essential reasons for its deactivation during the acid catalyzed reaction.