Hydroxylation Of Phenol Research Articles

Catalytic Performance and Kinetics of the Precursor of [Fe]-Hydrogenase in the Reaction of Phenol Hydroxylation in Aqueous Phase at Ambient Temperature

FeI2(CO)3PPh3, which usually used as the precursor of [Fe]-hydrogenase, was firstly used as catalyst in one-step hydroxylation of phenol to dihydroxybenzenes. It was found that the reaction can be conducted smoothly in aqueous phase at ambient temperature (25 °C). In the optimum conditions, the conversion of phenol is 26.7% and selectivity of DHB is 80.0%. The possible mechanism was investigated and proposed. The apparent kinetics study shows that it is a pseudo second order reaction and activation energy Ea is 66.36 kJ/mol.

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.

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.

Synthesis and characterization of hierarchical titanium-containing silicas using different size templates

The development of hierarchical catalytic heterogeneous catalytic systems with a controlled micro/mesopore ratio is an important issue in catalysis. The main purpose of the paper is to the establish influence of the size of the template molecule on the main characteristics of hierarchical titanium-containing silicas (H-TS). The H-TS were successfully synthesized by a bi-template method using tetrapropylammonium hydroxide (TPAG) as permanent template of MFI topology and tetramethylammonium bromide (TMAB), tetraethylammonium bromide (TEAB), tetrabutylammonium hydroxide (TBAG), dodecyltrimethylammonium bromide (DTMAB), cetyltrimethylammonium bromide (CTAB), didecyldimethylammonium chloride (DDAC), tetradecylbenzyldimethylammonium bromide (TBDAB) as variable structure-directing agent (SDA) of a different size. The structure and morphology were characterized by X-ray diffraction, a Fourier transform infrared spectroscopy, a Raman spectroscopy, a scanning electron microscopy and low-temperature nitrogen adsorption-desorption. The catalytic properties of the prepared titanium-containing micro-mesoporous silicas for hydroxylation of phenol with $$\hbox {H}_{2}\hbox {O}_{2}$$ have been evaluated, and their activities have been compared with those of TS-1 with only micropores. The findings of the research illustrate that with an increase in the molecule volume of the structure-directing agent, there is a decrease in the proportion of the crystalline phase and in the degree of the inclusion of $$\hbox {Ti}^{4+}$$ atoms in the structure of the zeolite material. Increase in the volume of the structure-directing agent leads to the decrease of the crystallinity of the samples and decrease in the specific surface area of the material and in the specific volume of micropores. The result of this research will be used to create a theoretical model of controlled micro-/mesoporous ratio in silicas and it may open new perspectives for their potential application in selective oxidation reactions involving large molecules. SYNOPSIS Synthesis and characterization of hierarchical titanium-containing silicas produced by a bi-template method are reported. The findings of the research illustrate that the size of the template influences the main textural properties of titanium-containing silicas.

Tuning the oxidation state of copper in CuMgAl hydrotalcite using partially oxidized MoS2 for efficient hydroxylation of phenol

The CuMgAl ternary hydrotalcite (CuMgAl) has been reported to achieve the decomposition of H2O2 to OH for hydroxylation of phenol, and the key active site is Cu+. The Cu2+ must be converted to Cu+, which is a slow step that lowers the total reaction efficiency. Herein, the partially oxidized MoS2 loaded CuMgAl (PO-MoS2/CuMgAl-1.12) sample was designed to overcome this issue. As a variable valence metal the Mo can partly tune the Cu2+ to Cu+ by forming MoOCu electron transport system which enhances the catalytic performance of our catalyst.

Preparation of Efficient TS‐1 with Small Particle Size and Enhanced Framework Ti

AbstractCrystal size and framework Ti content are two main factors which influence catalytic performances of TS‐1 catalysts. Control over the crystal size and framework Ti of TS‐1 through the synthesis of TS‐1 in the presence of polyethylene glycol (PEG) is reported. The crystal size of TS‐1 sample synthesized in the presence of PEG, TS‐1‐PEG was 230 nm. However, the size of TS‐1 synthesized without PEG, standard sample, was 290 nm. The TS‐1‐PEG possess higher amount of framework Ti content and less anatase TiO2 in comparison with TS‐1. The catalytic reaction tests showed superior activity of TS‐1‐PEG toward hydroxylation of phenol and oxidation of dibenzothiophene, deep desulfurization of fuels, as a result of cooperative effects of smaller particle size and higher framework Ti content. Consequently, using safe and un‐expensive PEG polymer is a powerful approach to synthesize TS‐1 with small crystal size and high framework Ti content to make efficient TS‐1 catalyst.

Acid-redox bifunctional Fe/Al-AMS catalyst: Simultaneously oriented introducing Fe2O3 in the channels and Al in the framework of AMS and its enhanced catalytic performance

For the silica-supported catalysts, the acid-free property and weak interaction between metal active centers and silica cause great limitations in their catalytic applications. In this work, a modified metal-assisted templating method was designed for simultaneously introducing different metal sites into two different locations to obtain a novel bifunctional catalyst, in which the acid sites are produced by incorporating Al species in the framework and the redox sites are brought by encapsulating Fe2O3 in the channels of anionic surfactant-templated mesoporous silica (AMS), respectively. The functionalized Fe-APTES micelles establish a critical effect between the surfactant head groups and silica species by counterion-mediated interaction, and the adjustable pH value makes the co-hydrolysis of Al species and silica resource. The results show that Fe2O3 are highly dispersed in the channels with a strong interaction, and the framework Al species produce large amount of weak Lewis acid sites. The reaction of phenol hydroxylation was proceeded under the condition of phenol/H2O2 = 1:2 (molar ratio), reaction temperature 30 °C, reaction time 4 h. For this reaction, the redox active sites and acid sites in Fe/Al-AMS catalysts are both effective. In specific, the well-dispersed Fe2O3 in the confined channels will provide more exposed active sites, and more importantly, by replacement of toxic mineral acids, a large amount of surface acid groups stimulates and adsorbs more hydroxyl radicals, leading to the improvement of catalytic activity, also for the selectivity of hydroquinone. Compared with the reference catalysts, by the synergic effect of the metal active centers and surface acid groups, 3Fe/Al-AMS catalyst displays the best catalytic performance (Conv. 46.6%, CAT Select. 49.9%, HQ Select. 33.3%) and stability in the phenol hydroxylation reaction. This oriented introduction pathway of multiple metals in different locations of silica reveals new vision in the development of multi-functional catalysts for other catalytic applications.

Synthesis of Hierarchical Titanium‐Rich Titanium Silicalite‐1 Zeolites and the Highly Efficient Catalytic Performance for Hydroxylation of Phenol

AbstractImproving the framework titanium (Ti) of titanium silicalite‐1 (TS‐1) zeolites and creating inter‐crystalline mesoporosity are two ways to enhance the catalytic properties of TS‐1 for hydroxylation of phenol. Most researches only used one of the ways. In this study, we successfully synthesized of hierarchical Titanium‐Rich (Ti‐rich) TS‐1. Ti‐rich TS‐1 was synthesized in the presence of ammonium carbonate ((NH4)2CO3). The framework Ti content of TS‐1 zeolites synthesized by different content of (NH4)2CO3 was studied by X‐ray fluorescence (XRF), Fourier transform infrared spectra (FTIR) and ultraviolet visible spectra, the framework Ti content was significantly increased by using (NH4)2CO3 as crystallization‐mediating agent. The synthesized samples were evaluated in hydroxylation of phenol. When the molar ratio of ammonium carbonate and tetraethyl orthosilicate in the synthesis gel was 0.2, the molar ratio of Si/Ti reached 34.43 and the Ti‐rich TS‐1 shows the optimum catalytic activity in hydroxylation of phenol. The post‐modification with aqueous solution of tetrapropylammonium hydroxide (TPAOH) was used to further improve the diffusion property. Compared with the parent TS‐1, the secondary pore volume was all increased. The developed hierarchical Ti‐rich TS‐1 zeolites were also assessed in hydroxylation of phenol. It was confirmed that hierarchical Ti‐rich titanium silicalite‐1 zeolites can improve the catalytic activity in phenol conversion considerably.

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

AbstractA new Fe(III)/MOF‐5(Ni) catalyst with high hydrostability was prepared using an equal load method under room temperature, and nearly 100% selectivity for catechol and 63.2% yield of dihydroxybenzene were obtained in hydroxylation of phenol with H2O2 over Fe(III)/MOF‐5(Ni) catalyst.

Phenol hydroxylation over Fe and Co-loaded mesoporous MCM-48

Iron and cobalt incorporated MCM-48 molecular sieves with Si/M = 40, 80 and 100 (where M is either iron or cobalt) have been synthesized using tetraethylorthosilicate as the silica source and cetyltrimethylammonium bromide as template under hydrothermal conditions. Characterization of the synthesized materials were done by XRD, SEM, UV–Vis., TGA, N2 adsorption–desorption and FTIR analysis. The XRD patterns of metal incorporated materials showed well-ordered MCM-48 structure and UV–Vis. study confirmed the sufficient incorporation of the metal ions in the tetrahedral coordination within the framework structure. The catalytic activity and selectivity of these catalysts were studied for liquid phase hydroxylation of phenol using H2O2 as oxidant. Catechol was obtained as major product whereas hydroquinone was obtained as a minor one.

Heterogeneous degradation of organic contaminants in the photo-Fenton reaction employing pure cubic β-Fe2O3

Pure cubic β-Fe2O3 crystal, which can absorb visible light (<650 nm) on account of the bandgap of 1.9 eV as a direct bandgap semiconductor, was employed as a low-cost and non-toxic catalyst for photo-Fenton reaction in this article. Diverse organic contaminants including rhodamine B (RhB), methyl orange (MO), alizarin red (AR) and phenol can be effectively degraded. In particular, the degradation of RhB were investigated detailedly. As such, hydroxyl radicals (OH) were verified to act as considerable active species for the process by using terephthalic acid as an indicator. Degradation mechanism and intermediates of phenol in the photo-Fenton reaction was discovered by virtue of liquid chromatography-mass spectrometry (LCMS). Notably, hydroxylation of phenol generated some intermediates, which are converted into H2O and CO2 eventually.

Modification of mordenite by carbon black template and utilization as supports for iron catalyst in phenol hydroxylation

Abstract The aim of this work was to prepare mordenite zeolite in sodium form by using silica-alumina source and carbon as the second template (C-NaMOR) then transformed to proton form (C-HMOR). Both C-NaMOR and C-HMOR were characterized by XRD and N2 adsorption-desorption to confirm their structure, morphology and textural properties including surface area, micro- and mesopores volume, respectively. Results from 27Al MAS NMR provided the information of structural defect corresponding to Bronsted and Lewis acid sites. NH3-TPD suggested the amount of acid increasing with structural defects. Both C-NaMOR and C-HMOR were impregnated with Fe(NO3)3⋅9H2O. The form of Fe in 5Fe/C-NaMOR and 5Fe/C-HMOR catalysts which analyzed by XANES was mainly Fe2O3 and the oxidation state was +3. Catalytic testing of Fe supported on C-xMOR zeolites showed improvement the conversions (68%) and selectivities (catechol/hydroquinone ratio = 1).

De novo synthesis of Cr-embedded MOF-199 and derived porous CuO/CuCr2O4 composites for enhanced phenol hydroxylation

MOF-derived CuCr2O4/CuO bimetallic oxides were synthesized for phenol hydroxylation with enhanced selectivity.

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.

Preparation and catalytic performance of alginate-based Schiff Base

As a biomass polymer, alginate-based material has drawn considerable attention and been applied in many fields. However, the research on alginate-based Schiff Base metal complex is scarce. Herein, a novel alginate-based Schiff Base Cu (II) complex was prepared via oxidation and imidization of alginate by periodate and organic amine, respectively. In additon, their catalytic performance in phenol hydroxylation reaction was investgated. Results illustrated that degree of oxidation had significant influence on metal loaded content. Compared with alginate, the alginate-based Schiff Base has more reactive groups, and can stablize more Cu cations which endowed their better catalytic activities.

Systematic Investigation for the Photocatalytic Applications of Carbon Nitride/Porous Zeolite Heterojunction

Here, we present the integration of a commercially available titanosilicate zeolite with photocatalyst graphitic carbon nitride (g-C3N4) toward the development of an effective heterojunction photocatalyst, TCN(1-8-8). The formation of this porous heterojunction and its structural details have been confirmed by X-ray diffraction, N2 adsorption, electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. The visible light absorption and band structure have been determined from diffused reflectance ultraviolet–visible spectroscopy. For its fabrication, the contents of both the constituent materials have been optimized systematically. Its photocatalytic activity has been found to be impressive in the visible light-assisted degradation of a variety of water pollutants (dyes and antibiotics) and in the hydroxylation of phenol. Control experiments, radical scavenging/trapping experiments, influence of the reaction environment, and photoelectroch...

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.

Insights into the effects of modifying factors on the solvent-free synthesis of FeAPO-5 catalysts towards phenol hydroxylation

A modified solvent-free method has been developed to synthesize FeAPO-5 zeolite catalysts with hierarchical porous structure as well as high crystallinity and iron content. The effects of mechanochemical and low-temperature pretreatment, as well as the addition of hydrogen peroxide and seed crystals on the synthesis of FeAPO-5 were studied in detail. The composition and structural features of relatively pure resultant products were deeply analyzed by XRD, SEM, ICP-AES, CHN analysis, TG–DTA, UV–Vis diffuse reflectance spectroscopy and N2 physisorption. Most importantly, low-temperature pretreatment towards H2O2-containing precursor mixtures can to a great degree improve the crystallinity of FeAPO-5 molecular sieve. Significantly, compared to the conventional micron-sized microporous FeAPO-5 zeolite, the hierarchical FeAPO-5 catalysts created by this modified solvent-free method show superior performance in phenol hydroxylation, in which the one with a high content of framework iron species exhibits the best catalytic performance, giving phenol conversion of about 40% and dihydroxybenzene selectivity of up to 80% at 50 °C within 3 h reaction time.

Synthesis of hierarchical titanium silicalite-1 in the presence of polyquaternium-7 and its application in the hydroxylation of phenol

Hierarchical titanium silicalite-1 (TS-1) without generated anatase TiO2 species was synthesized in the presence of polyquaternium-7 (M550) by one-step hydrothermal crystallization method and characterized by field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, X-ray fluorescence (XRF), Fourier transform infrared spectra, ultraviolet visible spectra, Raman spectroscopy and N2 adsorption–desorption measurements. The experimental results show that highly porous TS-1 crystals, with pores of ca. 2.6–4.9 nm diameter, are obtained under hydrothermal conditions by using polyquaternium-7 as the mesopore-directing agent. The polyquaternium-7 has a great influence on both the textural properties and the coordination of Ti species in the framework of TS-1. The catalytic properties and recyclability of the prepared mesoporous TS-1 for hydroxylation of phenol with H2O2 have been evaluated, and their activity has been compared with those of TS-1 with only micropores. The great catalytic activity, selectivity and stability of the hierarchical TS-1 as well as the cheap price and environmental-friendly nature of the used mesopore-directing agent allow to consider this hierarchical TS-1 as a promising catalyst for industry application.