Synergistic interactions between Ti–OOH and (PO₄[WO₂(O₂)]₄)^3- of HPW/Zn-Ti hydrotalcites: Efficient heterogeneous catalysts for the epoxidation of fatty acid methyl ester

A series of HPW/Zn-Ti layered double hydroxides (LDHs) were prepared by immobilizing phosphotungstic acid (HPW) on the Zn-Ti LDHs. Systematically characterizations were performed to elucidate their structure. These HPW/Zn-Ti LDHs hybrids were used as heterogeneous catalysts in the epoxidation of fatty acid methyl ester (FAMEs) with H₂O₂. The HPW/Zn-Ti LDHs showed higher activity than bulk HPW and Zn-Ti LDHs. The conversion of FAMEs and the selectivity to epoxy fatty acid methyl ester (EFAME) were up to 90.6 and 86.0%, respectively. (PO₄[WO₂(O₂)]₄)^3-was presumed to be the active site for the epoxidation in this work. The formed oxygen-donating intermediate Ti−OOH transferred oxygen free radicals to (PO₄[WO₂(O₂)]₄)^3- in the catalytic process, accelerating the transfer of oxygen free radicals. Therefore, high catalytic activity of HPW/Zn-Ti LDHs is related to the potential synergistic interactions of Ti−OOH and PW anions.