Ferrocene particles incorporated into Zr-based metal-organic frameworks for selective phenol hydroxylation to dihydroxybenzenes

UiO-66 with high dispersibility and a cuboctahedron morphology was synthesized by an improved solvothermal method. The morphology of UiO-66 was adjusted using benzoic acid as a modulator. UiO-66 with a regular morphology was then used as the support to load ferrocene (Fc). A series of Fc@UiO-66 composites were prepared via a facile impregnation method. The composites were characterized by powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), SEM/EDX mapping, FT-IR, UV/vis, TG analysis, N-2 adsorption-desorption, and X-ray photoelectron spectroscopy (XPS). The results showed that Fc was incorporated into UiO-66, thus preventing the agglomeration of Fc particles in water. The Fc@UiO-66 composites with a Fc loading of 5% (FU-5) exhibited the highest catalytic activity for hydroxylation of phenol with H2O2 at room temperature in water, which gave a phenol conversion of 38.5% and 87.4% selectivity for dihydroxybenzenes (DHB). UiO-66 played a crucial role in the enhancement of catalytic performance compared with conventional supports such as gamma-Al2O3, etc. A hydroxyl radical mechanism was proposed for this catalytic hydroxylation process and the high selectivity was attributed to the interaction between Fc particles and UiO-66.