Facile synthesis of polyoxometalates tethered to post Fe-BTC frameworks for esterification of free fatty acids to biodiesel

Abstract

A phosphomolybdic acid (PMA) was sequentially incorporated into highly porous metal–organic frameworks (MOFs, Fe-BTC) by using a facile one-pot synthesis method, and the prepared composite (PMA/Fe-BTC) was employed as an efficient and stable solid acid catalyst for biodiesel production. N₂ adsorption–desorption, X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), thermogravimetric (TG) analysis, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterization techniques were employed to reveal the structure–performance relationship. The effects of reaction parameters like catalyst amount, reaction time and temperature were further investigated. This solid acid gave good catalytic performance in the esterification of free fatty acids with methanol, which is attributed to large surface area and thermal stability. The PMA/Fe-BTC was successfully reused for up to six cycles and exhibited high stability. From the kinetic study performed at different reaction temperatures (140 °C, 150 °C and 160 °C) E_a = 49.5 kJ mol⁻¹ was obtained. In addition, due to the high activity presented in various esterifications of free fatty acids, this composite catalytic material has immense potential for industrial biodiesel production.