Mg–Fe mixed oxides as solid base catalysts for the transesterification of microalgae oil

Abstract

The Mg–Fe layered double hydroxide (Mg–Fe LDH) precursors were prepared using an improved urea method and characterized by XRD, ICP-AES and SEM analyses, indicating that the pH played a crucial role in the precipitation. The precipitation of the Mg–Fe LDH precursors was obtained when adjusting the initial pH to 9.3 by adding NaOH solution and controlling the urea/Fe³⁺ molar ratio as 36 in the precipitation solution at 110 °C for 10 h, where the relative yield was 85.4%. The calcined Mg–Fe LDH (LDO) was determined by XRD and CO₂-TPD analyses. The LDO with Mg/Fe molar ratio of 3 (LDO-3) was found to have the highest catalytic activity for the transesterification of microalgae oil due to its strongest basicity and highest crystallinity. Finally, the stability and the leaching of the catalytically active species as well as the reusability of the LDO-3 were confirmed by hot-filtration test and multiple reuses. The LDO-3 catalyst could be reused, but catalytic activity decreased after each run due to active species leaching although it retained high activity for the fourth use.