Catalysts For Hydroxylation Of Phenol Research Articles

Transition metal complexes of 4-hydroxy-3-methoxybenzaldehyde embedded in fly ash zeolite as catalysts for phenol hydroxylation

The focus of this work is to use fly ash, a waste generated by thermal power plants, to synthesize an economical and efficient heterogeneous catalyst for the fine chemicals industry. To achieve this goal, fly ash zeolite (FAZ) was prepared from fly ash and Cu(II), Ni(II) and Co(II) complexes of 4-hydroxy-3-methoxybenzaldehyde [M(VAN)-FAZ] were loaded in the channels of zeolite matrix by flexible ligand strategy. The prepared FAZ was characterized by XRD, SEM, FT-IR, TGA, XRF and BET analyses. Encapsulation of metal complexes in zeolite gains the advantage of heterogeneity thereby facilitating easy separation of products and selectivity. The incorporation of metal complexes in the framework of FAZ was further assured by FT-IR, XRD, TGA, AAS and UV–Visible analyses of M(VAN)-FAZ. Thermographs indicated a loading of 6.70–16.09% of the metal complexes in FAZ. The –OH stretching reported at 3184 cm−1 for the free ligand was absent in the FT-IR spectra of the encapsulated metal complexes, indicating the binding of this group with the metal ion. The loading of metal complexes in the pores of FAZ have been further confirmed by AAS reports. The FAZ encapsulated transition metal complexes of vanillin have been established as catalysts for phenol hydroxylation. The extent of phenol conversion increased with time, after 240 min, 90% phenol conversion was observed and the preferential catalytic activity of [M(VAN)-FAZ] was observed as: [Cu(II)(VAN)-FAZ] > [Co(II)(VAN)-FAZ] > [Ni(II)(VAN)-FAZ]. The products were characterized by GC-MS analysis and the recyclability of the prepared catalyst was assessed up to three cycles.

A Type of MOF-Derived Porous Carbon with Low Cost as an Efficient Catalyst for Phenol Hydroxylation

Using MOF-5 as a template, the porous carbon (MDPC-600) possessing high specific surface area was obtained after carbonization and acid washing. After MDPC-600 was loaded with Cu ions, the catalyst Cu/MDPC-600 was acquired by heat treatment under nitrogen atmosphere. The catalyst was characterized by X-ray powder diffraction (XRD), N2 physical adsorption (BET), field emission electron microscope (SEM), energy spectrum, and transmission electron microscope (TEM). The results show that the Cu/MDPC-600 catalyst prepared by using MOF-5 as the template has a very high specific surface area, and Cu is uniformly supported on the carrier. The catalytic hydrogen peroxide oxidation reaction of phenol hydroxylation was investigated and exhibits better catalytic activity and stability in the phenol hydroxylation reaction. The catalytic effect was best when the reaction temperature was 80°C, the reaction time was 2 h, and the amount of catalyst was 0.05 g. The conversion rate of phenol was 47.6%; the yield and selectivity of catechol were 37.8% and 79.4%, respectively. The activity of the catalyst changes little after three cycles of use.

Synthesis and characterization of new binuclear Co(II) and Ni(II) complexes derived from N, N′-bis(4-dimethyl-aminobenzylidene)-benzene-1,3-diamine as active catalysts for hydroxylation of phenol and their antibacterial properties

In the current study, both of Ni(II) and Co(II) complexes were derived from N,N′-bis(4-dimethyl-aminobenzylidene)-benzene-1,3-diamine as a novel ligand. The ligand and complexes were characterized by elemental analysis (CHNS), Fourier transform infrared spectroscopy (FT-IR), Ultraviolet–visible spectroscopy (UV–Vis), ESI mass spectroscopy, conductance, and magnetic moment measurements. Regarding magnetic moment measurements and spectral studies, an octahedral structure was suggested. The free ligand and metal complexes were evaluated in vitro against three bacterial pathogens, including; Staphylococcus aureus, Escherichia coli, and Bacillus subtilis. The growth inhibition zone of Ni(II) and Co(II) complexes was far more extended than the norm. Furthermore, we studied the catalytic activity of these complexes through the hydroxylation of phenol. Comparisons revealed that the catalytic performance of the Ni(II) complex was considerable than that of the Co(II) complex. Four parameters (i.e., duration of reaction, temperature, catalyst amount, and oxidant amount) were regarded for Ni(II) complex (as a catalyst) to achieve an optimum condition for hydroxylation of phenol. Ultimately, adequate time for the reaction was recognized in the 2 h duration and at 60 °C.

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.

Two Synthesis Methods for Fe(III)@MOF‐5‐derived Porous Carbon Composites for Enhanced Phenol Hydroxylation

AbstractMOF‐5‐derived porous carbon (MDPC) materials, MDPC‐600 and MDPC‐1000, were prepared by pyrolysis at 600 °C in nitrogen atmosphere prior to acid treatment and at 1000 °C in nitrogen atmosphere, respectively. The samples were characterized by X‐ray diffraction (XRD), Brunauer–Emmett–Teller (BET), scanning electron microscopy (SEM), X–MaxN energy spectrum, and transmission electron microscopy (TEM). The test results of MDPC‐1000 and MDPC‐600 show that both are microporous amorphous carbon with the 2.7 nm diameter pore size, indicating that the micropore of MOF‐5 is well preserved during pyrolysis. MDPC‐1000 and MDPC‐600 have specific surface areas of 1570.9 m2/g and 1029.5 m2/g, respectively. MDPC‐1000 and MDPC‐600 were loaded with Fe ions to prepare Fe(III)/MDPC composite materials, which were used as catalysts for phenol hydroxylation. The results show that Fe(III)/MDPC‐1000 has higher catalytic effect than Fe(III)/MDPC‐600. During one hour phenol hydroxylation at 80 °C with 3 wt.% Fe concentration and a mass ratio of catalyst to phenol of 0.053, Fe(III)/MDPC‐1000 provides maximum phenol conversion, dihydroxybenzene yield, and dihydroxybenzene selectivity of 61.4%, 54.3%, and 88.4%, respectively.

Structural and Functional Characterization of 4-Hydroxyphenylacetate 3-Hydroxylase from Escherichia coli.

The hydroxylation of phenols into polyphenols, which are valuable chemicals and pharmaceutical products, is a challenging reaction. The search for green synthetic processes has led to considering microorganisms and pure hydroxylases as catalysts for phenol hydroxylation. Herein, we report the structural and functional characterization of the flavin adenine dinucleotide (FAD)-dependent 4-hydroxyphenylacetate 3-monooxygenase from Escherichia coli, named HpaB. It is shown that this enzyme enjoys a relatively broad substrate specificity, which allows the conversion of a number of non-natural phenolic compounds, such as tyrosol, hydroxymandelic acid, coumaric acid, hydroxybenzoic acid and its methyl ester, and phenol, into the corresponding catechols. The reaction can be performed by using a simple chemical assay based on formate as the electron donor and the organometallic complex [Rh(bpy)Cp*(H2 O)]2+ (Cp*: 1,2,3,4,5-pentamethylcyclopentadiene, bpy: 2,2'-bipyridyl) as the catalyst for FAD reduction. The availability of a crystal structure of HpaB in complex with FAD at 1.8 Å resolution opens up the possibility of the rational tuning of the substrate specificity and activity of this interesting class of phenol hydroxylases.

Green energy-efficient synthesis of Fe-ZSM-5 zeolite and its application for hydroxylation of phenol

Abstract Currently, there remains a great challenge to synthesize zeolites in an energy-saving and environmentally friendly manner. Herein we report a novel solvent-free route of synthesizing Fe-ZSM-5 zeolite, which is featured by using Fenton's reagent as a promoter. The influences of crystallization time, amount of hydrogen peroxide and low-temperature pretreatment on the synthesis of Fe-ZSM-5 zeolite were investigated in detail. The results indicate that the combination of solvent-free synthesis with Fenton's reagent can facilitate the rapid crystallization of Fe-ZSM-5 zeolite. The resultant Fe-ZSM-5 zeolite was used as a catalyst for phenol hydroxylation, and characterized by XRD, SEM, ICP-AES, N2 physisorption and UV–Vis diffuse reflectance spectroscopy. Notably, it exhibits a much better catalytic performance as compared with the reference catalyst by conventional solvent-free method. The observed enhanced catalytic performance for this Fe-ZSM-5 catalyst is attributed to its larger BET surface area and mesoporous volume as well as enrichment towards phenol.

Formation of iron active species on HZSM-5 catalysts by varying iron precursors for phenol hydroxylation

Iron-containing HZSM-5 zeolite (Fen+-HZSM-5) are performed by ion exchange method with varying iron precursors of Fe2+, Fe3+ and equivalent molar of Fe2+/Fe3+. The Fen+-HZSM-5 materials are used as catalysts for phenol hydroxylation in the presence of H2O2. Bulk-iron oxides of α-Fe2O3 and α-FeOOH are synthesized via hydrothermal method for catalytic comparison to Fen+-HZSM-5. The iron structures on the Fen+-HZSM-5 catalysts are determined using UV–vis DRS and EXAFS techniques. The iron species found in the Fe2+-HZSM-5 and Fe3+-HZSM-5 catalysts is an isolated Fe3+ ion in tetrahedral geometry. Iron-oxo bonds with oxygen in zeolite framework (Fe-OF) are identified on both catalysts. On the other hand, Fe-O bond distances and coordination number on Fe2+/Fe3+-HZSM-5 exhibit the mixture of iron-oxo and iron-dioxo species (FO-Fe-OF) in octahedral geometry. The present iron species in the Fe2+/Fe3+-HZSM-5 catalyst show a significant improvement of the turnover number (TON) for phenol hydroxylation in comparison to the bulk α-Fe2O3 and α-FeOOH catalysts. Moreover, the existent iron-dioxo species on the Fe2+/Fe3+-HZSM-5 catalyst enhances catalytic selectivity to catechol product.

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.

Hydrothermal synthesis and characterization of aluminum-free Mn-β zeolite: a catalyst for phenol hydroxylation.

Zeolite beta, especially heteroatomic zeolite beta, has been widely used in the industries of fine chemicals and petroleum refining because of its outstanding thermal stability, acid resistance, and unique 3-D open-frame structure. In this paper, aluminum-free Mn-β zeolite was hydrothermally synthesized in the SiO2-MnO2-(TEA)2O-NaF-H2O system. The effect of the chemical composition of the precursor mixture to the crystallization of the Al-free Mn-β zeolite was investigated. The synthesized Al-free Mn-β zeolite was characterized by inductively coupled plasma (ICP), XRD, thermogravimetric/differential thermal analysis (TG/DTA), N2 adsorption-desorption, FT-IR, UV-vis, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). The results show that the synthesized zeolite has a structure of β zeolite with good crystallinity and Mn ions present in the framework of the zeolite. The synthesized Al-free Mn-β zeolite shows great catalytic activity toward the phenol hydroxylation reaction using H2O2 as the oxidant. Approximately 35% of phenol conversion and ∼98% of dihydroxybenzene selectivity can be obtained under the optimal conditions.

Influence of TiO2/TS-1 Calcination on Hydroxylation of Phenol

Titanium oxide (TiO2) was impregnated on the surface of titanosilicate-1 (TiO2/TS-1) and used as catalyst for hydroxylation of phenol with hydrogen peroxide. Calcination was conducted at various temperatures (400, 500, 600 and 700°C)in order to observe the effect on the structure and physicochemical properties towards catalytic activity for producing hydroquinone. The structure and physicochemical properties of the TiO2/TS-1 catalyst were characterized by several techniques, such as X-ray diffraction (XRD), infrared spectroscopy, nitrogen adsorption, pyridine adsorption and hydrophilic measurement. The results show that by increasing the calcination temperature,the surface acidity of the catalyst was also increased.TheTiO2/TS-1 catalyst calcined at 500°Cproved to be optimal for hydroquinone production, in which the anatase-rutile phase may be present dispersed on the MFI framework.

Preparation of ZrO2/Al2O3-montmorillonite composite as catalyst for phenol hydroxylation

Zirconium dispersed in aluminum-pillared montmorillonite was prepared as a catalyst for phenol hydroxylation. The effects of varying the Zr content on the catalyst’s physicochemical character and activity were studied with XRD, BET surface area analysis, surface acidity measurements and scanning electron microscopy before investigating the performance for phenol conversion. The zirconia dispersion significantly affects the specific surface area, the total surface acidity and surface acidity distribution related to the formation of porous zirconia particles on the surface. The prepared samples exhibited excellent catalytic activity during phenol hydroxylation.

Synthesis of Cu2(OH)PO4 Crystals with Various Morphologies and Their Catalytic Activity in Hydroxylation of Phenol

Abstract Copper hydroxyphosphate (Cu2(OH)PO4) crystals with various morphologies have been successfully synthesized by a simple hydrothermal method, using different organic amines as the morphology-controlling agents. These Cu2(OH)PO4 crystals were used as catalysts for phenol hydroxylation by H2O2, and they showed distinct activities. The sheet morphology of Cu2(OH)PO4 crystals with a large percentage of reactive facets ({011} facets) exhibited enhanced catalytic activity in hydroxylation of phenol.

Iron aluminium mixed pillared montmorillonite and the rare earth exchanged analogues as efficient catalysts for phenol oxidation

Iron aluminium mixed pillared montmorillonite prepared by partial hydrolysis method was exchanged with lanthanum, cerium and thorium metal salts. The pillared montmorillonite shows considerable increase in basal spacing and surface area. 27Al and 29Si nuclear magnetic resonance spectra show the presence of iron substituted Keggin cation as the pillaring species. Energy dispersive X-ray analysis shows the presence of about 2% rare earth metals. The prepared systems are excellent catalysts for hydroxylation of phenol underlining the use of eco-friendly clay catalysts for effective removal of pollutants. A detailed study of reaction variables suggests that oxidation of phenol increases with temperature and maximum conversion is obtained at 90°C. Hydroquinone selectivity increases with phenol concentration and time but decreases with temperature.

Synthesis of binary Cu–Pd–alginates dry bead and its high catalytic activity for hydroxylation of phenol

A series of binary Cu–Pd–alginate catalysts was prepared and their catalytic activities for phenol hydroxylation were investigated. The binary catalysts were characterized by UV–vis/DRS, FT-IR, ICP-AES, XPS, SEM and EDX measurements. The results of phenol hydroxylation illustrated that the conversions of phenol were associated with the immobilized content of the Cu 2 + ions, as well the selectivities to dihydroxybenzene were determined by the immobilized content of the Pd 2 + ions. The highest conversion of phenol catalyzed by Cu–Pd–ALG-30-1 was 53.9%, with selectivities to catechol and hydroquinone being 61.3% and 38.2%, respectively. ► Prepared Cu-Pd-alginate dry bead catalysts. ► Catalysts for phenol hydroxylation. ► Conversion of phenol was associated with the immobilized content of the Cu 2+ ions. ► Selectivity to dihydroxybenzene was associated with the immobilized content of the Pd 2+ ions.

Transition metal coordination polymers: Synthesis and catalytic study for hydroxylation of phenol and benzene

New coordination polymers of Ni(II) and Cu(II) of the polymeric salen-type Schiff base ligand derived from the condensation of 5,5′-methylene bis-(salicyaldehyde) with 1,2-diaminopropane yielded N,N′-1,2-propylenebis(5-methylenesalicylidenamine) abbreviated [CH2(H2sal-1,2-pn)]n have been synthesized. Both coordinated polymers with the general formula of [CH2(ML·XDMF)]n, where X=0, M=Cu; N,N′-1,2-propylenebis(5-methylenesalicylidenaminato)copper(II) and X=2, M=Ni; N,N′-1,2-propylenebis(5-methylenesalicylidenaminato)nickel(II) have been characterized by elemental analysis, magnetic susceptibility measurements, IR, electronic spectra and thermogravimetric studies. The ligand behaves as a bis-bidentate molecule coordinating through the phenolic oxygen and azomethine nitrogen atoms.These coordinated polymers have been assessed as catalysts for liquid phase hydroxylation of phenol and benzene using H2O2 as an oxidant. The results show a high activity and selectivity of both catalysts toward the formation of diphenols from phenol, and a low activity in the oxidation of benzene. The Cu-based catalyst exhibited higher activity than Ni-based catalyst for hydroxylation of phenol and benzene. The activity and efficiency of H2O2 depends on the reaction parameters viz., temperature, molar ratio of the reactants and the solvent. Concentration of the oxidant and other reaction parameters has been optimised for the maximum oxidation of these substrates. These catalysts can be recovered and reused without notable loss of activity.

Hydroxylation of phenol over rare earth exchanged iron pillared montmorillonites

Iron pillared montmorillonite prepared by partial hydrolysis method was exchanged with La, Ce and Th metal salts. The pillared montmorillonite showed considerable increase in basal spacing and surface area. EDAX showed presence of about 2% rare earth metals. 27Al and 29Si NMR spectra showed relaxation effects due to iron paramagnetic centres. The prepared systems are excellent catalysts for hydroxylation of phenol underlining the use of environmentally friendly clay catalysts for effective removal of pollutants. A detailed study of reaction variables suggests that oxidation of phenol increases with temperature and maximum conversion is obtained at 80 °C. Hydroquinone selectivity increases with phenol and solvent concentrations but decreases with time.

Microporous carbon molecular sieve as a novel catalyst for the hydroxylation of phenol

A series of microporous carbon-based catalysts were prepared by acidification and/or oxidization treatment of a commercially available carbon molecular sieve (CMS). The resultant samples were characterized by Boehm titration, X-photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), point of zero charge (pH PZC) test, N 2 adsorption, and inductively coupled plasma atomic emission spectrometry (ICP-AES), and employed as catalysts for phenol hydroxylation with H 2O 2. It is found that the acidic functional groups of CMSs play an important role for the catalytic performance. The effects of solvents, reaction temperature, ratio of phenol/catalyst, ratio of phenol/H 2O 2 and reaction time were investigated. Over the sample with the strongest surface acidity among the studied CMSs, the phenol conversion, the selectivity to dihydroxybenzene, and the effective utilization of H 2O 2 reach 29.6%, 85.1% and 80%, respectively under optimal reaction condition. The catalyst is stable in the recycling test. Furthermore, due to its easy physical separation, environmental benignity and low cost, the microporous CMSs is promising for industrial application.

A bio-generated Fe(iii)-binding exopolysaccharide used as new catalyst for phenol hydroxylation

The hydroxylation of phenol with aqueous H2O2 to afford catechol and hydroquinone was studied in a biphasic reaction medium, as well as in pure water, in the presence of a bio-generated iron(III) catalyst. This catalyst was purified from a culture of Klebsiella oxytoca BAS-10 growing under anaerobic conditions, with Fe(III)-citrate as the energy and carbon source. The overproduction of an exopolymer (EPS) encrusted bacterial cells. The EPS, binding Fe3+, (Fe-EPS), was extracted and studied before and after a reaction with phenol. Some of the reaction’s parameters, such as temperature, pH, and molar ratio between reagents and catalyst, were investigated to identify the best compromise between conversion and selectivity. The results could be useful either from a synthetic point of view or to support the biodegradation of aromatic substrates.

Pyridine-keggin heteropoly compounds as catalyst for hydroxylation of phenol using hydrogen peroxide as oxidant

The pyridine-heteropoly compounds are very active catalysts for phenol hydroxylation to dihydroxybenzenes with hydrogen peroxide as oxidant in aqueous solutions. The conversion of phenol reaches 77.8%, and the selectivity for dihydroxybenzenes reaches 99%.