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.