Bimetallic Ce-Cr doped metal-organic frameworks as a heterogeneous catalyst for highly efficient biodiesel production from insect lipids

Abstract

Conventional biodiesel production uses a homogeneous catalyst for the conversion of vegetable and animal oils. There is still a need for active, selective, and stable heterogeneous catalysts for the synthesis of biodiesel. Simultaneously incorporating Ce and Cr ions into the metal-organic framework during the crystallization process produced a new recyclable bimetal-doped metal-organic framework (Ce-Cr/ZIFs-8) nanocomposite catalyst in this study. The characterization techniques used, including XRD, SEM, N2 adsorption isotherms, and FT-IR, provide strong evidence of the successful integration of the two cations into the material framework. The addition of Ce and Cr ions has been found to have an impact on the framework's growth and introduces new features to ZIFs-8. The Ce to Cr ratio is the factor that determines the extent of the interconnection and hybrid MOF formation. Subsequently, biodiesel was produced using the Ce-Cr/ZIFs-8 catalyst by converting insect lipids. As expected, the comparison of the conversion behavior of biodiesel from ZIFs-8 and Ce-Cr/ZIFs-8 materials shows that exposed metal sites play a key role in MOF conversion performance. A high biodiesel yield of 92.06% was achieved under optimum conditions (molar ratio of Ce/Cr = 2:1, molar ratio of Ce-Cr/Zn = 20:1, molar ratio of methanol/lipid = 10:1, and catalyst concentration of 2.5 wt% at 65 °C for 8 h). Regeneration experiments revealed that the regenerated catalyst exhibited good catalytic potency after being reused four times (75.66%). Moreover, a reasonable mechanism was proposed to explain the reasons for conversion behavior. The physicochemical properties of the produced biodiesel from insect lipids match the requirements of the ASTM standard.