Development of VCl3-free synthetic routes for MIL-100(V) and its application in heterogeneous catalysis

Abstract

This research investigates the development of sustainable, VCl₃-free synthetic routes for vanadium-containing MIL-100 metal-organic frameworks. Traditional VCl₃-based synthesis methods pose significant environmental and safety concerns due to the hazardous nature of the precursor. This study explores alternative vanadium sources, namely VOSO₄·5H₂O, V(acac)₃, and V₂O₅, through both direct solvothermal synthesis and bimetallic synthesis strategies. Material characterization was performed using powder X-ray diffraction, Fourier-transform infrared spectroscopy, thermogravimetric analysis, and X-ray fluorescence spectroscopy to evaluate crystallinity, structural stability, and elemental composition. Results reveal that direct synthesis routes typically yield materials with low crystallinity or phase impurities. In contrast, bimetallic synthesis of vanadium containing MIL-100(Fe) and MIL-100(Al) frameworks successfully preserves the characteristic MIL-100 topology while incorporating vanadium into the structure. Catalytic evaluations using tert-butyl hydroperoxide as oxidant demonstrate that vanadium-incorporated MIL-100 materials exhibit redox activity in the oxidation of diverse substrates, including cis-cyclooctene, thioanisole, benzyl alcohol, and benzoin. Complete conversion was achieved for benzoin oxidation, while other substrates showed partial conversion. The study concludes that vanadium-incorporated MIL-100 materials are promising catalysts for redox-mediated transformations, though catalytic efficiency depends critically on the uniformity and accessibility of active sites within the framework. While bimetallic synthesis strategies overcome synthesis barriers associated with direct crystallization, maintaining long-range order remains a critical challenge for optimizing the performance of vanadium-based MIL-100 frameworks in catalytic applications.