Mo-Modified Zirconium Phosphate Solid Acid Catalysts for Sustainable Biodiesel Production from Low-Value Acidic Oils

Abstract

To develop robust solid acid catalysts for the simultaneous transesterification and esterification of low-value oils into biodiesel, a Mo-modified zirconium phosphate (Mo/ZrP) catalyst was prepared via the intercalation of Mo precursors into layered ZrP using an impregnation method. N₂ adsorption-desorption, NH₃-TPD, and Py-FTIR analyses indicated that the 40%Mo/ZrP catalyst possesses a high specific surface area, hierarchically porous structures, and strong acidic properties. Such catalyst demonstrates outstanding performance, achieving 97% oil conversion under the optimal reaction conditions. Furthermore, the catalyst shows not only high resistance to free fatty acid (FFA) and water, but good reusability, maintaining oil conversion of >85% after five reuse cycles. This performance meets the requirements for biodiesel production from low-quality oil feedstocks containing moisture and FFA. As evidenced by XRD, UV–vis-DRS, and H₂-TPR results, the intercalation of Mo species can induce strong interactions between the layered ZrP and Mo, enhancing catalytic stability by preventing the leaching of acidic Mo species. Additionally, the synergistic effect between Brønsted and Lewis acid sites contributes to excellent co-catalysis ability for simultaneous transesterification and esterification in acidic oil conversion.