Abstract
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.
Highlights
The hydroxylation of phenol to catechol (CTL) and hydroquinone (HQ) is a prominent industrial reaction
Catalysts consumption of H2O2), the adsorbed phenol seems to evolve into more complex molecules, postulated as the tar component, according to the broad peak detected by differential scanning calorimetry (DSC)-thermogravimetric analysis (TGA) (Figure S1)
At the end of the reaction, the adsorbed phenol seems to evolve into more complex molecules, postulated as the tar component, according to the broad peak detected by DSC-TGA (Figure S1)
Summary
The hydroxylation of phenol to catechol (CTL) and hydroquinone (HQ) is a prominent industrial reaction. Metal–organic frameworks (MOFs) are novel hybrid materials constructed from organic ligands and inorganic metal ions Due to their inherent porosity and well dispersed active sites, MOFs are potential catalysts in a wide number of reactions [11,12,13,14]. New environmentally favorable synthesis methods have been reported [11,18], allowing the use of MOFs in some large-scale applications This method usually sacrifices some properties like crystallinity or porosity [19]. The key issue in view of their actual application is the stability of the MOF-based catalysts, in particular when liquid phase media are involved [24] This necessitates the examination of the stability of MOF catalysts under a wider range of operational conditions in order to select those that avoid the leaching of the metals.
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