Defective Ce-Doped Mixed Ligand-UiO-66 MOFs with Controlled Fluorination for CO₂ Conversion: Synthesis and Thorough Characterization

UiO-66 is one of the most robust and versatile MOFs, widely employed in gas adsorption, catalysis, and separation. Recently, defect engineering on this material has gained more attention: missing linker and cluster defects can be selectively introduced to create more reactive exposed metal sites. Additionally, substituting Zr Lewis acid sites with Ce ions can enhance reactivity, particularly towards the conversion of CO₂ and methanol into dimethyl carbonate (DMC)[1]. This reaction is important for CO₂ fixation, as DMC is a greener alternative to phosgene and dimethyl sulphate, used in polycarbonate synthesis, carbonylations, methylations, and fuel additives. Studies on Zr and Ce-based MOF-derived oxides have shown that water produced during the reaction deactivates Ce sites, lowering catalytic activity[2]. Using UiO-66 to maintain an even distribution of active sites, could slow water diffusion to Lewis acid centres and improving activity. Moreover, trifluoroacetic acid-modulated UiO-66 catalysts have demonstrated improved performance in DMC synthesis[3], highlighting the role of hydrophobicity in water expulsion. With this in mind, we succeeded in the synthesis of a series of potential Zr0.9Ce0.1-UiO-66 catalytic systems by substituting the ligand with fluorinecontaining ones and applying a mixed linkers approach by introducing mixtures of fluorinated and non-fluorinated ligands at different ratios. These materials are subject of a deep characterization, involving PXRD, porosimetry, TGA, SEM-EDX and ICP-OES analysis as well as synchrotron radiation techniques, HR-PXRD and in-operando AP-XAS.