Solvent-Free Synthesis and Characterization of Bimetallic UiO-66(Zr/Sn) Heterogeneous Catalyst for Biodiesel Production

It has been verified that UiO-66(Zr) is an effective heterogeneous catalyst for the production of biodiesel. The construction of multimetal sites in the structure of UiO-66(Zr) can be a promising way to enhance the catalytic performance of UiO-66(Zr). In this contribution, UiO-66(Zr) with tin sites is simply fabricated under solvent-free conditions. The results from XRD, EDX, and XPS analyses indicate that tin species have been introduced into the structure of UiO-66(Zr). The nitrogen sorption data show that UiO-66(Zr/Sn)-5-130-24 obtained under optimized synthesis conditions maintains a large BET specific surface area (1170 m²/g) and pore volume (0.84 cm³/g). The NH₃-TPD results reveal that UiO-66(Zr/Sn)-5-130-24 possesses more acid sites than UiO-66(Zr) probably because the introduction of tin species brought about the missing of linkers in the structure of UiO-66(Zr). As a consequence, UiO-66(Zr/Sn)-5-130-24 exhibits higher catalytic efficiency with an oleic acid conversion of 98.8% than UiO-66(Zr) (oleic acid conversion of 86.2%) at 333 K in the esterification reaction of oleic acid with methanol to obtain biodiesel. Furthermore, the reusability test demonstrates that such a catalyst can be readily recycled and reused.