Cerium‐Organic Framework UiO‐66(Ce) as a Support for Nanoparticulate Gold for Use in Oxidation Catalysis.

An optimised synthesis of the metal‐organic framework (MOF) UiO‐66(Ce) is reported using a modulator‐free route, yielding ~5 g of material with high crystallinity and 22 % ligand defect. Two methods are developed for loading gold nanoparticles onto the MOF. The first uses a double‐solvent method to introduce HAuCl4 onto UiO‐66(Ce), followed by reduction under 5 % H2 in N2, while the second is a novel one‐pot method where HAuCl4 is added to the synthesis mixture, forming Au nanoparticles within the pores of the UiO‐66(Ce) during crystallisation. Analysis using powder X‐ray diffraction (PXRD), nitrogen adsorption isotherms, transmission electron microscopy and small‐angle X‐ray scattering (SAXS) reveals that the two‐step double‐solvent method yields gold crystallites on the external surface of the MOF particles that are visible by PXRD. In contrast, the one‐pot method forms smaller gold crystallites, with a distribution of sizes centred on ~4 nm diameter as seen by SAXS, with evidence from PXRD for the smallest particles being present within the MOF structure. The Au‐loaded UiO‐66(Ce) materials are evaluated for the catalytic oxidation of vanillyl alcohol to vanillin at 60 °C. Our findings indicate that incorporating Au nanoparticles via the one‐pot synthesis method, enhances redox activity, achieving 43 % conversion and 90 % selectivity towards vanillin. [ABSTRACT FROM AUTHOR]