Hydroxylation Of Phenol Research Articles

Solvothermal Synthesis of Fe-MOF-74 and Its Catalytic Properties in Phenol Hydroxylation

A Fe-containing metal-organic framework, Fe-MOF-74, was solvothermally synthesized using FeCl2.4H2O and 2,5-di-hydroxy-1,4-benzenedicarboxylic acid. Characterization was conducted by XRD, BET surface area measurement, FT-IR spectroscopy, TGA, and elemental analysis, which confirmed successful preparation of Fe-MOF-74 having an identical framework structure to that reported for MOF-74. Fe-MOF-74 was found to be an effective heterogeneous catalyst for the hydroxylation of phenol using H2O2 as an oxidant; 60% phenol conversion was achieved at 20 degrees C in water with 68 and 32% selectivity to catechol and hydroquinone, respectively. The effect of temperature, phenol/H2O2 mole ratio, catalyst quantity, and solvent on catalytic performance was discussed, and a reaction mechanism is proposed based upon the experimental results.

Synthesis and Catalytic Activity of Cu(II), Fe(III) and Bi(III) Complexes of Thio-Schiff Base Encapsulated in Zeolite-Y for Hydroxylation of Phenol

Coordination of 4-{[(1E)-(2-hydroxyphenyl)methylene]amino}-2,4-dihydro-3H-1,2,4-triazole-3-thione, [sal(thiotriazol)], with M-exchanged zeolite-Y (M = Cu(II), Fe(III) and Bi(III)) leads to the encapsulation of the metal complexes in the supercages of zeolite-Y by flexible ligand method. The prepared encapsulated metal complexes have been characterized by physico-chemical techniques, which indicated that the complexes were effectively encapsulated inside the supercages of Na–Y, without any modification of the morphology and structure of the zeolite. 3D model structure generated for these complexes suggests that zeolite-Y can accommodate these complexes in the FAU supercages without any strain. The catalytic activity of all the catalysts towards the hydroxylation of phenol was evaluated under heterogeneous conditions using hydrogen peroxide as an oxidant. Under the optimized conditions, these catalysts show moderate activity with excellent selectivity (>95%) towards catechol. These catalysts were stable in hydroxylation of phenol and have been reused a further three times after recovering. The results reflect the reusability of the catalysts, as no significant loss in their catalytic activity was noticed.

Catalytic Role of Cu Sites of Cu/MCM-41 in Phenol Hydroxylation

Four types of copper-containing MCM-41 mesoporous silicas were synthesized by the surface organometallic chemistry (SOMC) procedure (Cu/MCM-41-S), mechanical mixing (Cu/MCM-41-M), impregnation (Cu/MCM-41-I), and the hydrothermal technique (Cu/MCM-41-H). The resultant samples were characterized in detail by X-ray diffraction (XRD), N(2) physical adsorption, transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), temperature-programmed reduction (TPR), and infrared spectroscopy (IR) of NO adsorption. Catalytic behaviors of these samples for hydroxylation of phenol with H(2)O(2) were evaluated. The results revealed that depending on the preparation methods the samples contain different copper-oxo species and thus show different catalytic behaviors. Among these samples, the one prepared by SOMC contains a predominant amount of isolated Cu(2+) and exhibits the most excellent catalytic activity and selectivity. The amount of isolated copper species decreases in the order of Cu/MCM-41-S > Cu/MCM-41-H > Cu/MCM-41-I > Cu/MCM-41-M, while the amount of copper oxide clusters increases in a reversal order. The difference in the catalytic activity and product selectivity of these four samples could be rationally explained by the distinction of chemical states of copper species. The highly dispersed isolated Cu(2+) species are identified as the active sites in the phenol hydroxylation, while the nonisolated Cu(2+) clusters or oxide are responsible for the deep oxidation of primary product HQ and the decrease of product selectivity. The mechanism of the copper-catalyzed phenol hydroxylation was proposed.

Cloning, purification and characterization of two components of phenol hydroxylase from Rhodococcus erythropolis UPV-1

Phenol hydroxylase that catalyzes the conversion of phenol to catechol in Rhodococcus erythropolis UPV-1 was identified as a two-component flavin-dependent monooxygenase. The two proteins are encoded by the genes pheA1 and pheA2, located very closely in the genome. The sequenced pheA1 gene was composed of 1,629 bp encoding a protein of 542 amino acids, whereas the pheA2 gene consisted of 570 bp encoding a protein of 189 amino acids. The deduced amino acid sequences of both genes showed high homology with several two-component aromatic hydroxylases. The genes were cloned separately in cells of Escherichia coli M15 as hexahistidine-tagged proteins, and the recombinant proteins His(6)PheA1 and His(6)PheA2 were purified and its catalytic activity characterized. His(6)PheA1 exists as a homotetramer of four identical subunits of 62 kDa that has no phenol hydroxylase activity on its own. His(6)PheA2 is a homodimeric flavin reductase, consisting of two identical subunits of 22 kDa, that uses NAD(P)H in order to reduce flavin adenine dinucleotide (FAD), according to a random sequential kinetic mechanism. The reductase activity was strongly inhibited by thiol-blocking reagents. The hydroxylation of phenol in vitro requires the presence of both His(6)PheA1 and His(6)PheA2 components, in addition to NADH and FAD, but the physical interaction between the proteins is not necessary for the reaction.

Highly Enhanced Phenol Hydroxylation in [h0h]-Oriented Fe–ZSM-5 Membranes

Catechol (CAT) and hydroquinone (HQ) are two important diphenol isomers with a variety of industrial applications. The hydroxylation of phenol catalyzed by transition metal (TM) substituted ZSM-5 is an environmentally benign route for diphenol production, which is usually governed by intracrystalline diffusion. Therefore, the availability of highly oriented TM-ZSM-5 membranes and their utilization in an interphase membrane reactor can significantly promote the hydroxylation of phenol. The continuous and [h0h]-oriented Fe-ZSM-5 membrane on the porous α-Al 2 O 3 was prepared using a new seeded growth method. Characterization was carried out by using SEM, XRD, UV/Vis, and EPMA techniques, which demonstrated that the [h0h]-oriented membrane consists of Fe substituted ZSM-5 crystal grains with an Si/Fe ratio of approximately 75. Compared with the catalytic performance of different sized Fe-ZSM-5 grains loaded in the traditional slurry reactor, the [h0h]-oriented Fe-ZSM-5 membrane in the interphase membrane reactor showed significantly improved phenol conversion and selectivity for CAT and HQ due to the molecular path control in the zeolite membranes.

Surface characterization and catalytic evaluation of copper-promoted Al-MCM-41 toward hydroxylation of phenol

The Mobil Composition of Matter No. 41 (MCM-41) containing Cu and Al with Si/Al ratios varying from 100 to 10 and 1 to 6 wt.% of Cu was synthesized under hydrothermal and impregnation conditions, respectively. The samples were characterized by nitrogen adsorption–desorption measurements, X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), UV–Vis diffuse reflectance spectroscopy (UV–Vis DRS), temperature-programmed reduction (TPR), temperature-programmed desorption (TPD), and 29Si and 27Al magic-angle spinning–nuclear magnetic resonance (MAS–NMR) spectra. X-ray diffraction patterns indicate that the modified materials retain the standard MCM-41 structure. TPR patterns show the two-step reduction of Cu species. TPD study shows that Cu-impregnated Al-MCM-41 samples are more acidic than Al-MCM-41. From the MAS–NMR it was confirmed that most of the Al atoms are present tetrahedrally within the framework and some are present octahedrally in extraframework position. Impregnation of Cu shifted Al to the extraframework position. The catalytic activity of the samples toward hydroxylation of phenol in aqueous medium was evaluated using H 2O 2 as the oxidant at 80 °C. The effects of reaction parameters such as temperature, catalyst amount, amount of H 2O 2, and solvent were also investigated. Sample containing 4 wt.% copper-loaded Al-MCM-41-100 showed high phenol conversion (78%) with 68% catechol and 32% hydroquinone selectivity.

Characterization of AlMCM-41 synthesized with rice husk silica and utilization as supports for platinumiron catalysts

RH-MCM-41 was synthesized by using silica from rice husk and further modified to increase acidity by adding Al with grafting method with Si/Al ratio of 75 and 25. The resulting materials were referred to as RH-AlMCM-41(75) and RH-AlMCM-41(25). The XRD spectra of all RH-AlMCM-41 confirmed a mesoporous structure of MCM-41. Surface areas of all RH-AlMCM-41 were in the range of 700-800 m2/g, lower than that of the parent RH-MCM-41, which was 1230 m2/g. After Al addition the Si/Al ratios of RHAlMCM-41(75) and RH-AlMCM-41(25) were higher than that of the parent RH-MCM-41. The RH-AlMCM41 materials were used as supports for bimetallic platinum-iron catalysts, denoted as Pt-Fe/RH-AlMCM-41, with Pt and Fe amounts of 0.5 and 5.0% by weight, respectively. Results from TPR indicated that the presenceof Al might assist the interaction between Pt and Fe as the reduction temperature of iron oxides shifted to a lower value. All catalysts were active for phenol hydroxylation using H2O2 as an oxidant, for which the highest conversions were observed on the RH-MCM-41 material with the highest surface area. The acidity of the supports did not present a significant role in improving the catalytic performance.

Flexible ligand synthesis, characterization and liquid phase hydroxylation of phenol by H2O2 with host (nanopores of zeolite-Y)/guest [VO([R]2–N2X2)]2+ (R = H, CH3; X = NH, O, S) nanocomposite materials

Encapsulation of Oxovanadium(IV) complexes of 12-membered macrocyclic ligands having N2O2, N2S2 and N4 donor atoms in the nanocavity of zeolite-Y by the Flexible-Ligand Method (FLM) have been described. Oxovanadium(IV) complexes with macrocyclic ligands were entrapped in the nanocavity of zeolite-Y by a two-step process in the liquid phase: (i) adsorption of precursor ligand; 1,2-di(o-aminophenyl-, amino, oxo, thio)ethane, (N2X2); in the supercages of VO(IV)-Y; ([VO(N2X2)]2+-Y (X = NH, O, S); and (ii) in situ condensation of the oxovanadium(IV) precursor complex with glyoxal or biacetyl; [VO([R]2–N2X2)]2+-Y (R = H, CH3). The new Host–Guest Nanocomposite Materials (HGNM, [VO([R]2–N2X2)]2+-Y) have been characterized by FT-IR, DRS and UV–Vis spectroscopic techniques, XRD and elemental analysis, as well as nitrogen adsorption. Liquid-phase selective hydroxylation of phenol with H2O2 to a mixture of catechol and hydroquinone in CH3CN has been reported using [VO([R]2–N2X2)]2+-Y as catalysts. Reaction conditions have been optimized by considering the concentration of substrate and oxidant, amount of catalyst, effect of time, volume of solvent and temperature. Under the optimized reaction conditions, [VO([H]2–N4)]2+-Y gave 50.1% conversion of phenol after 6 h. All these catalysts are more selective toward catechol formation.

Binuclear μ-hydroxo-bridged iron clusters derived from surface organometallic chemistry of ferrocene in cavities of HY zeolite: Local structure, bound sites, and catalytic reactivity

Binuclear iron clusters were constructed successfully in cavities of HY Zeolite by surface organometallic chemistry (SOMC) of ferrocene. UV–visible diffuse reflection (UV–vis DRS), X-ray absorption fine structure (XAFS), electron paramagnetic resonance (EPR), and infrared (IR) spectroscopies were used to characterize the structure of the formed binuclear iron clusters. The results show that the majority is presented as binuclear μ-hydroxo-bridged iron clusters consisting of a [Fe III–( μ-OH)–Fe III] core, which is anchored on the zeolite framework by the bonding of Fe atom and bridging O sites that lie in a plane of a 12-membered ring connecting the supercages. These binuclear iron clusters show better catalytic reactivity towards phenol hydroxylation than large iron oxide clusters. Iron oxide as active component was found to represent a nuclearity-related catalytic behavior for phenol hydroxylation. The decrease in nuclearity of iron oxides from nanoparticles to binuclear iron clusters leads to the increase in conversion and to the drastic decrease in induction time.

Preparation of titanium silicalite-1 catalytic films and application as catalytic membrane reactors

Titanium silicalite-1 (TS-1) films were prepared on porous α-Al 2O 3 tubes using nanosized silicalite-1 (Sil-1) particles as seeds by hydrothermal treatment and a TS-1 catalytic membrane reactors (CMR) was reasonably designed and evaluated by phenol hydroxylation with hydrogen peroxide as oxidant. Some factors on influencing TS-1 film formation and catalytic properties were investigated and the TS-1 films were characterized by scanning electron microscope (SEM), transmission electron micrograph (TEM), X-ray diffractometer (XRD), FTIR, UV–vis and X-ray fluorescence (XRF). It was indicated that TS-1 films prepared from Sil-1 and TS-1 seeds were comparable in structure, morphology and reaction behavior. The crystallization time and times of TS-1 film had a strong effect on its morphology, thickness and orientation. However, the film thickness could be easily controlled by crystallization time and times. The Ti/Si ratio in synthesis solution intensely influenced the content of the titanium atoms incorporated as framework Ti that was correlated well with the activity. The maximum Ti (IV) incorporated corresponds to a Ti/Si ratio of approximately 0.02–0.03. A constant conversion for phenol hydroxylation was obtained with the film thickness of over 7.5 μm. It is demonstrated that most of the reaction occurred in a shallow layer near the film due to the mass transfer effects in the TS-1 films.

Effects of pore structure of post-treated TS-1 on phenol hydroxylation

The present study reports the effects of crystal size of TS-1 (micrometer sized umTS1 and nanometer sized nmTS1) and the post-treatment (TPAOH and NaOH treatment) on the porous structure and the catalytic performances of TS-1 in phenol hydroxylation. TPAOH post-treatment generates hollow crystal and increases the surface area of umTS1 without changing its pore structure. In contrast, NaOH treatment selectively dissolves framework silica to form mesopore and modify microporous structure through which hierarchical material is constructed with agglomerated crystals. The umTS1 sample gives a much lower conversion and lower selectivity of dihydroxylbenzenes (DHB) than the nmTS1 sample. Its activity can be greatly improved by TPAOH post-treatment exhibiting a comparable catalytic activity and DHB selectivity with the nmTS1 sample. Furthermore, successive post-treatment by TPAOH following with NaOH can generate micropores larger than the pore size of TS-1. The higher titanium content and faster diffusivity associated with the successive post-treatment significantly improve the catalytic performance of TS-1.

Cobalt(II), Copper(II) and Zinc (II) complexes of 2-methyl benzimidazole encapsulated in zeolite as catalysts for the hydroxylation of phenol

Cobalt(II), Copper(II) and Zinc (II) complexes of 2-methylbenzimidazole (Mebzlh) encapsulated in the super cages of zeolite-Y and ZSM-5 have been synthesized by flexible ligand method and characterized by various physico-chemical measurements. The catalytic activity of encapsulated complexes was investigated for the decomposition of H2O2 and for the hydroxylation of phenol using H2O2 as an oxidant. The hydroxylation of phenol yielded catechol and hydroquinone as the major products. All catalysts show good selectivity for diphenol products. The results showed that conversion of phenol varies in the order [Cu(Mebzlh)]-Y > [Cu(Mebzlh)]-ZSM-5 > [Zn(Mebzlh)]-Y > [Co(Mebzlh)]-Y > [Zn(Mebzlh)]-ZSM-5 > [Co(Mebzlh)]-ZSM-5 after 6 h of reaction time.

Hybrid macromolecular iron and copper complexes in the phenol hydroxylation reaction

Macromolecular iron and copper complexes based on hybrid materials with grafted polyamine polymers have been synthesized. It has been shown that the silica gel-immobilized iron complexes with polyallylamine-supported EDTA and copper complexes with polyethyleneimine exhibit a high activity in phenol hydroxylation with hydrogen peroxide. The catalysts can be recycled without the loss of activity.

Di-, tri- and tetra-valent ion-exchanged NaY zeolite: Active heterogeneous catalysts for hydroxylation of benzene and phenol

Abstract Ion-exchanged NaY zeolite with various valent cations are tested for hydroxylation of benzene and phenol with H 2 O 2 in 1:1 and 3:1 molar ratios, respectively; the highest conversion of benzene (33%) in green one-step process is achieved using Cu–NaY with 100% selectivity to phenol, while OV–NaY shows >36% phenol conversion with 91% selectivity to catechol, whereas TOF exceeds 1000 with Zn–NaY after 6 h reaction time which is among the highest value reported so far.

Phenol Hydroxylation over Alkaline Treated TS-1 Catalysts

Alkaline treatment on TS-1 can selective remove silica from the framework while MFI zeolitic framework remains intact, which creates new large micropores or even mesopores and increases Si/Ti ratio in the alkaline treated TS-1. Among various alkaline hydroxide, CsOH treatment leads to partial destruction of MFI structure. All the desilicated TS-1 samples show enhanced phenol conversion and dihydroxylbenzene (DHB) yield in acetone solvent by two folds, which can be attributed to the higher Ti/Si ratio and improved diffusivity. Pore structure modified with alkaline treatment affects significantly reaction pathway and product selectivity. The initial product over the parent TS-1 and NaOH treated TS-1 is mainly 4-hydroxycyclohexa-2,5-dienone and catechol enriched DHB, respectively.

Model Study on a Submerged Catalysis/Membrane Filtration System for Phenol Hydroxylation Catalyzed by TS-1

This research is focused on the development of a simple design model of the submerged catalysis/membrane filtration (catalysis/MF) system for phenol hydroxylation over TS-1 based on the material balance of the phenol under steady state and the reported kinetic studies. Based on the developed model, the theoretical phenol conversions at steady state could be calculated using the kinetic parameters obtained from the previous batch experiments. The theoretical conversions are in good agreement with the experimental data obtained in the submerged catalysis/MF system within relative error of ±5%. The model can be used to determine the optimal experimental conditions to carry out the phenol hydroxylation over TS-1 in the submerged catalysis/MF system.

Synthesis of Iron Phthalocyanine Grafted onto SBA-15 through Single Siloxane Bond and its Application in Liquid-Phase Hydroxylation of Phenol

For a long time, iron phthalocyanines are well known as efficient oxidation catalysts. However, the use of ungrafted tert-butyl-substituted iron phthalocyanine (tBuPcFe) complexes is severely limited by the necessity of their isolation from the reaction mixtures after catalytic reactions. This drawback can be avoided by applying their immobilization upon the surface of inorganic supports such as silica gel, MCM-41 or SBA-15. Immobilization of tBuPcFe can be performed through simple adsorption, [1] coordinative bonding with an anchoring group[2,3] and covalent bonding with surface silanol groups of the support.[4] Both free and heterogenized tBuPcFe complexes have been shown to be active in oxidation of cyclohexane,[5] phenol,[2] 2,3,6-trimethylphenol[4] and 2-methyl-1-naphthol.[6] The covalent attaching of Pc complex is also possible by siloxane bond if Pc has an (alkoxy)3Si-containing substituent. In this case siloxane bond is formed between a silicon atom of Pc and oxygen atom of support surface. Iron(III) phthalocyanine complexes symmetrically substituted by (EtO)3Si functional groups were described previously,[7] but monomeric derivatives seem to be more suitable for controlled immobilization that affords a stable heterogeneous catalyst with spatially separated active iron species.

Characterization of platinum–iron catalysts supported on MCM-41 synthesized with rice husk silica and their performance for phenol hydroxylation

Mesoporous material RH-MCM-41 was synthesized with rice husk silica by a hydrothermal method. It was used as a support for bimetallic platinum−iron catalysts Pt–Fe/RH-MCM-41 for phenol hydroxylation. The catalysts were prepared by co-impregnation with Pt and Fe at amounts of 0.5 and 5.0 wt.%, respectively. The RH-MCM-41 structure in the catalysts was studied with x-ray diffraction, and their surface areas were determined by nitrogen adsorption. The oxidation number of Fe supported on RH-MCM-41 was + 3, as determined by x-ray absorption near edge structure (XANES) analysis. Transmission electron microscopy (TEM) images of all the catalysts displayed well-ordered structures, and metal nanoparticles were observed in some catalysts. All the catalysts were active for phenol hydroxylation using H2O2 as the oxidant at phenol : H2O2 mole ratios of 2 : 1, 2 : 2, 2 : 3 and 2 : 4. The first three ratios produced only catechol and hydroquinone, whereas the 2 : 4 ratio also produced benzoquinone. The 2 : 3 ratio gave the highest phenol conversion of 47% at 70 °C. The catalyst prepared by co-impregnation with Pt and Fe was more active than that prepared using a physical mixture of Pt/RH-MCM-41 and Fe/RH-MCM-41.

Theoretical study of the hydroxylation of phenols mediated by an end-on bound superoxo–copper(II) complex

Peptidylglycine alpha-amidating monooxygenase and dopamine beta-monooxygenase are copper-containing proteins which catalyze essential hydroxylation reactions in biological systems. There are several possible mechanisms for the reductive O(2)-activation at their mononuclear copper active site. Recently, Karlin and coworkers reported on the reactivity of a copper(II)-superoxo complex which is capable of inducing the hydroxylation of phenols with incorporated oxygen atoms derived from the Cu(II)-O(2) (.-) moiety. In the present work the reaction mechanism for the abovementioned superoxo complex with phenols is studied. The pathways found are analyzed with the aim of providing some insight into the nature of the chemical and biological copper-promoted oxidative processes with 1:1 Cu(I)/O(2)-derived species.

Theoretical study of the hydroxylation of phenolates by the Cu2O2(N,N′-dimethylethylenediamine)2 2+ complex

Tyrosinase catalyzes the ortho hydroxylation of monophenols and the subsequent oxidation of the diphenolic products to the resulting quinones. In efforts to create biomimetic copper complexes that can oxidize C-H bonds, Stack and coworkers recently reported a synthetic mu-eta(2):eta(2)-peroxodicopper(II)(DBED)(2) complex (DBED is N,N'-di-tert-butylethylenediamine), which rapidly hydroxylates phenolates. A reactive intermediate consistent with a bis-mu-oxo-dicopper(III)-phenolate complex, with the O-O bond fully cleaved, is observed experimentally. Overall, the evidence for sequential O-O bond cleavage and C-O bond formation in this synthetic complex suggests an alternative mechanism to the concerted or late-stage O-O bond scission generally accepted for the phenol hydroxylation reaction performed by tyrosinase. In this work, the reaction mechanism of this peroxodicopper(II) complex was studied with hybrid density functional methods by replacing DBED in the mu-eta(2):eta(2)-peroxodicopper(II)(DBED)(2) complex by N,N'-dimethylethylenediamine ligands to reduce the computational costs. The reaction mechanism obtained is compared with the existing proposals for the catalytic ortho hydroxylation of monophenol and the subsequent oxidation of the diphenolic product to the resulting quinone with the aim of gaining some understanding about the copper-promoted oxidation processes mediated by 2:1 Cu(I)O(2)-derived species.