Synthesis of SO42−/TiO2-ZnAl2O4 composite solid acids as the esterification catalysts

Abstract

A series of novel sulfated ZnAl2O4-TiO2 (SO42−/ZnAl2O4-TiO2) composite solid acids were synthesized for the esterification of biomass derived acids. The properties were characterized by XRD, FT-IR, XPS, NH3-TPD, acid-base titration, TG and FE-SEM. The experimental results showed that the introduction of ZnAl2O4 spinel oxide played a key role in stabilizing the structure of the composite catalysts as well as the surface sulfate groups. The composition of SO42−/TiO2-ZnAl2O4 catalysts significantly influenced their catalytic properties and performance in esterification reactions. The optimal SO42−/ZnAl2O4-TiO2 (6 : 4) catalyst with the largest number of acid sites showed superior conversion of 95.8% in oleic acid esterification and 98.5% conversion in acetic acid esterification. Moreover, the SO42−/ZnAl2O4-TiO2 (6 : 4) catalyst showed excellent reusability in these reactions, which was ascribed to its stable structure and good resistance of the surface sulfate groups. The efficient and reusable SO42−/ZnAl2O4-TiO2 composite solid acid coupled with spinel modification is expected to bring new opportunities in the design of favorable acid catalysts.