Catalytic Hydroxylation Of Phenol Research Articles

Super-Stable Mineralization of Metal Ions from Smelting Wastewater by In Situ Synthesis of NiFe-Based Layered Double Hydroxides for Catalytic Phenol Hydroxylation.

The super-stable mineralization of metal ions from industrial wastewater by in situ synthesis of layered double hydroxides (LDHs) has been regarded as a sustainable approach from environmental protection and resource utilization perspectives. Herein, the study reports a super-stable mineralization of metal ions including Ni, Fe, Cr, Mn, Cu, Ca, Al, etc. from smelting wastewater by in situ synthesis of NiFe-based LDHs through facile coprecipitation. Such approach exhibits superior mineralization efficiency of metal ions simultaneously that can remove hundreds, thousands, or even tens of thousands mg/L of multiple metal ions to below the values of the Chinese National Emission Standards of Pollutants. Furthermore, the obtained NiFe-based LDHs exhibit excellent catalytic performance of phenol hydroxylation due to the mineralization of multiple metals on the laminates, where 48.24% conversion of phenol and 71.58% selectivity of dihydroxybenzenes are realized under room temperature for 3h. This work paves a sustainable strategy for hazardous material disposal and resource utilization.

Novel bioinspired diiron core complexes with rigid chelating diphosphine ligands for highly efficient catalytic phenol hydroxylation

Hydroquinone (HQ) and catechol (CAT) are the important raw materials in the chemical industry, which can be produced through a direct catalytic hydroxylation process using hydrogen peroxide as an oxidant. Herein, we report two novel diiron core complexes (μ-budt)Fe2(CO)5(DPEphos) (1) and (μ-budt)Fe2(CO)5(Xantphos) (2) supported by rigid heterocyclic xanthene-like diphosphine ligands which exhibit high selectivity and activity in phenol hydroxylation. The structures of complexes 1 and 2 were characterized by FT-IR, UV–vis, 1H NMR, 31P-NMR, X-ray crystallography, while the catalytic products were tested by using HPLC. The FT-IR and UV–vis spectra reveal that two diphosphine ligands exhibit similar impacts on the structure of parent complex (μ-budt)Fe2(CO)6 [budt = SCH(CH3)CH2CH2)S]. Despite the similarity of ligands’ impact on the structure of the parent complex, the catalytic behavior was strongly influenced by the electronic and steric effects. The factors influencing the catalytic activity were optimized, including catalyst dosage, phenol/ H2O2 molar ratio, reaction temperature, and time. Under the optimal conditions, 1 exhibits great catalytic performance with 57.7% phenol conversion and 49.6% DHB yield, both of which are remarkable. The mechanism of phenol hydroxylation using 1 as a catalyst was also proposed. Hydroxyl radicals (•OH) were generated in the catalytic reaction, as demonstrated by electron spin resonance (ESR).

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: Cphenol,0 = 0.33 M, Cphenol,0/CH2O2,0 = 1:1 molar, WR = 2.2 g, and space time (τ = W·QL-1) = 0-147 gcat·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 (SDHBZ) of 100% with a yield (YDHBZ) 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 (SDHBZ = 99.1% and YDHBZ = 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.

Enhanced catalytic phenol hydroxylation by CuZnFeAl layered double hydroxides: synergistic effects of Cu+ and oxygen vacancies

In this work, a series of CuZnFeAl-LDH catalysts for phenol oxidation to dihydroxybenzene have been prepared through a co-precipitation method.

Fabrication and catalytic performance of meso-ZSM-5 zeolite encapsulated ferric oxide nanoparticles for phenol hydroxylation

An encapsulation-structured Fe2O3@meso-ZSM-5 (Fe@MZ5) was fabricated by confining Fe2O3 nanoparticles (ca. 4 nm) within the ordered mesopores of hierarchical ZSM-5 zeolite (meso-ZSM-5), with ferric oleate and amphiphilic organosilane as the iron source and meso-porogen, respectively. For comparison, catalysts with Fe2O3 (ca. 12 nm) encapsulated in intra-crystal holes of meso-ZSM-5 and with MCM-41 or ZSM-5 phase as the shell were also prepared via sequential desilication and recrystallization at different pH values and temperatures. Catalytic phenol hydroxylation performance of the as-prepared catalysts using H2O2 as oxidant was compared. Among the encapsulation-structured catalysts, Fe@MZ5 showed the highest phenol conversion and hydroquinone selectivity, which were enhanced by two times compared to the Fe-oxide impregnated ZSM-5 (Fe/Z5). Moreover, the Fe-leaching amount of Fe@MZ5 was only 3% of that for Fe/Z5. The influence of reaction parameters, reusability, and · OH scavenging ability of the catalysts were also investigated. Based on the above results, the structure-performance relationship of these new catalysts was preliminarily described.

Facile Synthesis of CuMgFe Layered Double Hydroxides for Efficient Catalytic Phenol Hydroxylation under Mild Conditions

AbstractA series of CuMgFe layered double hydroxides (denoted as X/CuMgFe–LDHs) with different Cu contents were synthesized by co‐precipitation as catalysts for phenol hydroxylation under mild conditions. The as‐prepared samples were analyzed by X‐ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma emission spectroscopy (ICP‐ES), N2 adsorption–desorption, Fourier transform infrared (FT‐IR), thermogravimetric differential scanning calorimetry (TG‐DSC), X‐ray photoelectron spectroscopy (XPS) and hydrogen temperature‐programmed reduction (H2‐TPR) to investigate the morphologies and physicochemical properties. As presented by the characterization results, introducing a certain amount of copper not only increased the amount of active metal centers but also formed more oxygen vacancies and lattice oxygen to promote electron transport between the double layers in LDHs. However, the excess copper would significantly disrupt the X/CuMgFe–LDH framework, declining the activity. Therefore, the 20/CuMgFe–LDH sample presented the best catalytic performance among all the catalysts in terms of activity, which was correlated with the layered structure, low‐temperature reducibility, oxygen species and low Cu+/Cu2+ and Fe2+/Fe3+ ratios. The catalyst could maintain good stability even after recycling for five times. Finally, a possible mechanism for phenol hydroxylation via Cu+–OV–Fe2+ and Cu2+–O–Fe3+ redox cycles on CuMgFe–LDHs was proposed.

Hydroxylation of Phenol Catalyzed by Iron Metal-Organic Framework (Fe-BTC) with Hydrogen Peroxide

Liquid phase catalytic hydroxylation of phenol by Fe-containing metal-organic framework, Fe-BTC (BTC = 1,3,5-benzenetricarboxylate) using 30% H2O2 as an oxidant and H2O as solvent showed good activity and stability under mild reaction conditions. Phenol reacts with hydrogen peroxide over Fe-BTC to produce two main products, viz., catechol and hydroquinone. The effect of temperature, time, substrate/hydrogen peroxide mole ratio and amount of catalyst on catalytic performance were studied. The catalyst could be reused four times without losing significant loss of catalytic performance. The crystallinity and structure of catalyst were unchanged during the catalysis reaction, as confirmed by comparison of XRD and SEM of the fresh and reused catalyst. A reaction mechanism is proposed based on the experimental results.

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.

Aqueous-phase catalytic hydroxylation of phenol with H2O2 by using a copper incorporated apatite nanocatalyst.

Copper incorporated apatite (Cu-apatite) nanomaterial was prepared by a co-precipitation method. The obtained material was characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) and Raman spectroscopy, scanning electron microscopy (SEM, STEM) and nitrogen adsorption–desorption. The as-prepared Cu-apatite was used to catalyze phenol hydroxylation with hydrogen peroxide as an oxidant. The influencing parameters including reaction time, temperature, H2O2/phenol ratio and catalyst mass have been investigated. Under the optimized conditions, the Cu-apatite catalyst gave a phenol conversion of 64% with 95% selectivity to dihydroxybenzenes. More importantly, the results of catalyst recycling indicated that the same catalytic performance has been obtained after four cycles with a slight loss of activity and selectivity.

Catalytic hydroxylation of phenol to dihydroxybenzene by Fe(II) complex in aqueous phase at ambient temperature

Inspired by natural [Fe]-hydrogenase, mono-iron complex FeII(CO)3I3-[trimethylpyridine-H] (complex 1) was synthesized and characterized by IR, 1H NMR, 13C NMR, EA. The singe crystal structure of the complex 1 was characterized by single crystal X-ray diffraction. The hydroxylation reaction of phenol to dihydroxybenzene was conducted using complex 1 as catalyst in aqueous phase at ambient temperature. Under the optimum conditions, the phenol conversion was 20.5%, dihydroxybenzene selectivity was 83.7%, catechol/hydroquinone (mol/mol) was 2.6. Complex 1 can be a promising catalyst for hydroxylation of phenol to dihydroxybenzene because of mild reaction conditions and good catalytic performance.

Catalytic hydroxylation enables phenol to efficient assembly of ordered mesoporous carbon under highly acidic conditions

As an important route towards the preparation of ordered mesoporous carbon (OMC), the aqueous assembly method with phenol as precursor still faces a challenge of yielding an OMC under acidic conditions because of the formation of thermoplastic resin in acidic conditions, which leads to structure collapse during carbonization. Herein, we developed an approach combined catalytic hydroxylation of phenol with assembly process to prepare OMC under acidic conditions. In our route, phenol was first partially converted into highly reactive phenols (catechol and hydroquinone) by catalytic hydroxylation, and the resulted mixture of phenols then interacted with template of Pluronic block copolymer F127 under acidic conditions to form a thermosetting mesophase through phase separation, which was carbonized to form OMC. The obtained carbon possesses ordered mesostructure with surface area of 435 m2/g, pore volume of 0.41 cm3/g and achieves high capacitance of 231 F/g for supercapacitor compared to that of normal mesoporous carbon (151 F/g) and activated carbon (AC, 119 F/g), which may be attributed to its high oxygen content resulted from catalytic hydroxylation. The developed strategy not only affords a novel approach for the synthesis of OMC but also provides a way to introduce pseudocapacitive oxygen on ordered mesoporous carbon.

Preparation of Fe/activated carbon directly from rice husk pyrolytic carbon and its application in catalytic hydroxylation of phenol

The loading of iron and the formation of activated carbon were combined to one step and the thus-obtained Fe/activated carbon showed good catalytic performance for phenol hydroxylation.

Liquid-phase catalytic hydroxylation of phenol using metal crosslinked alginate catalysts with hydrogen peroxide as an oxidant

A series of divalent metal (Cu, Co, Ni, Fe, Mn, Zn and Pd) crosslinked alginate dry beads catalysts were prepared using metal chloride and sodium alginate. The resulting catalysts were characterized by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, inductively coupled plasma atomic emission spectroscopy, scanning electron microscopy, energy-dispersive X-ray analyses and nitrogen physisorption measurements. The characterization results showed that a series of ion-crosslinked metal-alginate dry beads were synthesized through ion exchange, followed by the coordination of alginate and metal ions. These materials have been assessed as catalysts for liquid-phase hydroxylation of phenol to dihydroxybenzenes using H2O2 as an oxidant. The results showed that Cu-based catalyst exhibited higher activity than other metal-based catalysts for phenol hydroxylation. The influence of key reaction parameters, including the reaction temperature, solvent, reaction time, initial pH, molar ratio of phenol/H2O2 and the amount of catalyst on the reactivity and selectivity were also investigated. Finally, the reusability of Cu-based catalyst illustrated that it could be recovered and reused without notable loss of activity.

Catalytic Phenol Hydroxylation with Dioxygen: Extension of the Tyrosinase Mechanism beyond the Protein Matrix

A new catalyst (see structure) hydroxylates phenols with O2 via a stable side-on peroxide complex, which is similar to the active site of tyrosinase in terms of the ligand environment and its spectroscopic properties. The catalytic oxidation of phenols to quinones proceeds at room temperature in the presence of NEt3 and even non-native substrates can be oxidized catalytically. The reaction mechanism is analogous to that of the enzyme-catalyzed reaction.

Synthesis, structural characterization and catalytic activity study of Mn(II), Fe(III), Ni(II), Cu(II) and Zn(II) complexes of quinoxaline-2-carboxalidine-2-amino-5-methylphenol: Crystal structure of the nickel(II) complex

Five new transition metal complexes [MnL(OAc)]·H 2O ( 1), [FeLCl 2] ( 2), [NiL 2]·H 2O ( 3), [CuLCl] ( 4) and [ZnL 2]·2H 2O ( 5) have been synthesized using a tridentate Schiff base ligand, HL (quinoxaline-2-carboxalidine-2-amino-5-methylphenol) and the complexes have been characterized by physicochemical and spectroscopic techniques. The spectral analyses reveal an octahedral geometry for 3, square pyramidal structure for 2 and square planar structure for 4. Analytical and physicochemical data indicate tetrahedral structure for 1 and octahedral structure for 5. The crystallographic study reveals that [NiL 2]·H 2O shows distorted octahedral geometry with a cis arrangement of N 4O 2 donor set of the bis Schiff base and exhibits a two-dimensional polymeric structure parallel to [0 1 0] plane. The complexes were screened for catalytic phenol hydroxylation reaction. Coordinatively unsaturated manganese(II), iron(III) and copper(II) complexes were found to be active catalysts. The poor catalytic activity of the nickel(II) complex is due to coordinatively saturated octahedral nature of the complex. Maximum conversion of phenol was observed for the copper(II) complex and the major product was catechol.

CATALYTIC PERFORMANCES OF Fe&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt;/TS-1 CATALYST IN PHENOL HYDROXYLATION REACTION

Hydroxylation reaction of phenol into diphenol, such as hydroquinone and catechol, has a great role in many industrial applications. Phenol hydroxylation reaction can be carried out using Titanium Silicalite-1 (TS-1) as catalyst and H2O2 as an oxidant. TS-1 catalyst shows high activity and selectivity for phenol hydroxylation reaction. However, its hydrophobic sites lead to slow H2O2 adsorption toward the active site of TS-1. Consequently, the reaction rate of phenol hydroxylation reaction is tends to be low. Addition of metal oxide Fe2O3 enhanced hydrophilicity of TS-1 catalyst. Liquid phase catalytic phenol hydroxylation using hydrogen peroxide as oxidant was carried out over iron (III) oxide-modified TS-1 catalyst (Fe2O3/TS-1), that were prepared by impregnation method using iron (III) nitrate as precursor and characterized by X-ray diffraction, infrared spectroscopy, nitrogen adsorption, pyridine adsorption, and hydrophilicity techniques. Catalysts 1Fe2O3/TS-1 showed maximum catalytic activity of hydroquinone product. In this research, the increase of hydroquinone formation rate is due to the higher hydrophilicity of Fe2O3/TS-1 catalysts compare to the parent catalyst, TS-1. Keywords: Fe2O3/TS-1, hydrophilic site, phenol hydroxylation

Stable Bulky Particles Formed by TS‐1 Zeolite Nanocrystals in the Presence of H2O2

AbstractBulky particles of TS‐1 zeolite (larger than 20 μm) are successfully collected by simple filtration after crystallization of TS‐1 zeolite in the presence of H2O2. Bulky TS‐1 (B‐TS‐1) has good stability under both ultrasonic conditions and in recycling of the catalyst. Nitrogen isotherms show that B‐TS‐1 has a larger mesopore volume (0.55 cm3 g−1) than conventional TS‐1 nanocrystals (N‐TS‐1; less than 300 nm) obtained from high‐speed centrifugation (0.28 cm3 g−1). In catalytic hydroxylation of phenol with H2O2, both fresh (25 %) and recycled B‐TS‐1 (24 %) show similar high activities to N‐TS‐1 (28 %). B‐TS‐1 was further characterized by X‐ray diffraction, scanning electron microscopy, transmission electron microscopy, UV/Vis spectroscopy, and other techniques. The results suggest that bulky particles of B‐TS‐1 were formed by strong interactions of the nanocrystals with each other in the synthesis of TS‐1 zeolite. Such unique structural features might be responsible for the high stability of the bulky particles, large mesopore volume, and high catalytic activities in phenol hydroxylation, as well as the collection of B‐TS‐1 from a simple filtration route.

Anchoring of Fe(III)salicylamide onto MCM-41 for Catalytic Hydroxylation of Phenol in Aqueous Medium Using Hydrogen Peroxide as Oxidant

Fe(III)salicylamide immobilized on MCM-41 has been developed for hydroxylation of phenol in water medium using hydrogen peroxide as the oxidant. In the first step, the amine group containing 3-aminopropyltrimethoxy silane has been immobilized on the surface of MCM-41 via co-condensation. The amine group upon condensed with methyl salicylate afford a bidentate ligand in the mesoporous matrix for anchoring Fe(III) ions in the second step. Small angle XRD, N2 adsorption–desorption isotherms, 13C and 29Si cross-polarization magic angle spinning NMR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and diffuse reflectance UV–vis spectra were employed for the characterization of the catalysts. The heterogeneous iron salicylamide complex shows excellent catalytic activity in phenol hydroxylation using hydrogen peroxide as the oxidant and water as the solvent. Notably, phenol shows high conversion (64.6%) with very high selectivity for dihydroxybenzene compounds. The heterogeneous catalyst shows a successive slight decrease in catalytic activity when reused for three more times. Fe(III)salicylamide–MCM-41 has been synthesized successfully through an easy co-condensation route. XRD and N2 adsorption–desorption showed mesoporosity is retained even after complexation and FT-IR and diffuse reflectance UV–vis spectra confirmed the formation of complex. The heterogeneous catalyst exhibit excellent catalytic performance and stability in phenol hydroxylation reaction for the formation of dihydroxybenzene derivatives using H2O2.

Photocatalytic Hydroxylation of Phenol over Ti-Containing Zeolites (TS-1, Ti-MCM-41)

The photo-catalytic hydroxylation of phenol with hydrogen peroxide was carried out over TS-1 and Ti-MCM-41 catalysts. For comparison, the dark (thermal)-catalytic hydroxylation of phenol was also performed. The difference in catalytic behaviors of TS-1 and Ti-MCM-41 and product distribution in both the reactions were investigated. The TS-1 and Ti-MCM-41 catalysts having the Si/Ti ratio of 50 were prepared by in-situ crystallization and characterized using XRD, UV-DRS. In the all reactions, the main products were catechol (CAT), hydroquinone (HQ) and benzoquinone (BQ). In dark (thermal)-reaction, TS-1 showed a higher catalytic activity than Ti- MCM-41. In photo-reaction, however, the activity of Ti-MCM-41 was comparable to that of TS-1. The conversion of phenol and the selectivity to CAT in the photo-catalytic reaction were higher than those in dark (thermal)-reaction. In the all reactions, the selectivity to CAT increased remarkably when the selectivities to HQ and BQ decreased with reaction time.

The Synthesis of Copper(II) Salicylaldiminato Complexes and their Catalytic Activity in the Hydroxylation of Phenol

The synthesis of copper(II) salicylaldiminato complexes and their application in the catalytic hydroxylation of phenol is reported. Tetracoordinated copper complexes (Cu(Ln)2) were obtained by reacting the N-phenylsalicylaldimine ligands (HL1 -HL7) with copper acetate in a 2 : 1 mole ratio. The reaction of N-(2,6-diisopropyl)phenyl-3,5-di-tert-butylsalicylaldimine (HL7) with copper acetate in a 1 : 1 mole ratio afforded a dinuclear complex, which was not obtained with the other ligand systems. All complexes were characterized using FT-IR and elemental analysis. X-Ray crystal structures of complexes 2, 5 and 8 have also been obtained. The catalytic activity of these complexes was evaluated in the hydroxylation of phenol using oxygen and hydrogen peroxide as co-oxidants in aqueous media in the pH range 3 - 6. All complexes studied were found to be active for the hydroxylation process over the pH range studied with higher selectivity for catechol formation.