A New Fe(III)/MOF-5(Ni) Catalyst for Highly Selective Synthesis of Catechol from Phenol and Hydrogen Peroxide

The pioneering role of metal-organic framework-5 in ever-growing contemporary applications - a review

MOF-5 with a Zn(ii) cluster and terephthalic acid is a distinctive porous material among the metal–organic frameworks (MOFs), with unique physical, chemical and mechanical properties. MOF-5 based composites possess ample applications in modern chemistry. Huge surface area, suitable pore dimensions and scope of tunability make MOF-5 noteworthy in advanced materials. The extensive features of MOF-5 provided an opportunity for researchers to explore atomic/molecular scale materials. Various MOF-5 based composites have been designed with revamped properties appropriate to the application by altering and fabricating MOF-5 in situ or using a post-synthetic approach. Surface modification via the dispersion and impregnation of active substances into the pores of MOF-5 enhances its applicability. The boundless topologies and morphologies of MOF-5 combined with other chemical entities has provided opportunities in various fields, including catalysis, gas storage and sensors. The present review illuminates the leading role of MOF-5 and its composites in contemporary applications based on the current literature in heterogeneous catalysis, H₂ and CO₂ storage and sensors.

MOF-5 with a Zn(ii) cluster and terephthalic acid is a distinctive porous material among the metal–organic frameworks (MOFs), with unique physical, chemical and mechanical properties.

3D-Printed Fe/γ-Al2O3 Monoliths from MOF-Based Boehmite Inks for the Catalytic Hydroxylation of Phenol

The synthesis of dihydroxybenzenes (DHBZ), essential chemical reagents in numerous industrial processes, with a high degree of selectivity and yield from the hydroxylation of phenol is progressively attracting great interest in the catalysis field. Furthermore, the additive manufacturing of catalysts to produce 3D printed monoliths would provide additional benefits to enhance the DHBZ synthesis performance. Herein, 3D cellular Fe/γ-Al₂O₃ monoliths with a total porosity of 88% and low density (0.43 g·cm^-3) are printed by Robocasting from pseudoplastic Fe-metal-organic frameworks (Fe-MOF)-based aqueous boehmite inks to develop catalytic monoliths containing a Fe network of dispersed clusters (≤5 μm), nanoclusters (<50 nm), and nanoparticles (∼20 nm) into the porous ceramic skeleton. The hydroxylation of phenol in the presence of hydrogen peroxide is carried out at different reaction temperatures (65-85 °C) in a flow reactor filled with eight stacked 3D Fe/γ-Al₂O₃ monoliths and with the following operating conditions: C_phenol,0 = 0.33 M, C_phenol,0/C_H2O2,0 = 1:1 molar, W_R = 2.2 g, and space time (τ = W·Q_L^-1) = 0-147 g_cat·h·L^-1. The scaffolds present a good mechanical resistance (∼1 MPa) to be employed in a catalytic reactor and do not show any cracks or damage after the chemical reaction. DHBZ selectivity (S_DHBZ) of 100% with a yield (Y_DHBZ) of 32% due to the presence of the Fe network in the monoliths is reported at 85 °C, which represents an improved synthesis performance as compared to that obtained by using the conventional Enichem process and the well-known titanium silicalite-1 catalysts (S_DHBZ = 99.1% and Y_DHBZ = 29.6% at 80 °C). This printing strategy allows manufacturing novel 3D structured catalysts for the synthesis of critical chemical compounds with higher reaction efficiencies.

Direct Hydroxylation of Phenol to Dihydroxybenzenes by H2O2 and Fe-based Metal-Organic Framework Catalyst at Room Temperature

A semi-crystalline iron-based metal-organic framework (MOF), in particular Fe-BTC, that contained 20 wt.% Fe, was sustainably synthesized at room temperature and extensively characterized. Fe-BTC nanopowders could be used as an efficient heterogeneous catalyst for the synthesis of dihydroxybenzenes (DHBZ), from phenol with hydrogen peroxide (H2O2), as oxidant under organic solvent-free conditions. The influence of the reaction temperature, H2O2 concentration and catalyst dose were studied in the hydroxylation performance of phenol and MOF stability. Fe-BTC was active and stable (with negligible Fe leaching) at room conditions. By using intermittent dosing of H2O2, the catalytic performance resulted in a high DHBZ selectivity (65%) and yield (35%), higher than those obtained for other Fe-based MOFs that typically require reaction temperatures above 70 °C. The long-term experiments in a fixed-bed flow reactor demonstrated good Fe-BTC durability at the above conditions.

Preparation of Fe(II)/MOF-5 Catalyst for Highly Selective Catalytic Hydroxylation of Phenol by Equivalent Loading at Room Temperature

The metal-organic framework MOF-5 was synthesized by self-assembling of Zn(NO3)2·7H2O and H2BDC using DMF as solvent by the direct precipitation method and loaded with Fe2+ by the equivalent loading method at room temperature to prepare Fe(II)/MOF-5 catalyst and the microstructure, phases, and pore size of which was characterized by IR, XRD, SEM, TEM, and BET. It was found that Fe(II)/MOF-5 had high specific surface and porosity like MOF-5 and uniform pore distribution, and the pore size is 1.2 nm. In order to study the catalytic activity and reaction conditions of Fe(II)/MOF-5, it was used to catalyze the hydroxylation reaction of phenol with hydrogen peroxide. The results showed that the dihydroxybenzene yield of 53.2% and the catechol selectivity of 98.6% were obtained at the Fe2+ content of 3 wt.%, the mass ratio of Fe(II)/MOF-5 to phenol of 0.053, the reaction temperature of 80°C, and the reaction time of 2 h.