Hydroxylation Of Phenol Research Articles

Multisubstrate specific flavin containing monooxygenase from Chlorella pyrenoidosa with potential application for phenolic wastewater remediation and biosensor application

ABSTRACTMicrobial degradation of phenolic pollutants in industrial wastewater is dependent on enzymatic pathway comprising a cascade of phenol metabolizing enzymes. Phenol hydroxylase is the first enzyme of the pathway catalysing the initial attack on phenol in green algae Chlorella pyrenoidosa. The present work reports cost-effective production of partially purified microalgal phenol hydroylase by single-step purification and characterization of its kinetic properties with the view of application for enzyme-based remediation of phenolic wastewater or in phenolic biosensor. The enzyme with a molecular weight of 25 kDa shows all characteristics of phenol hydroxylases, that is, hydroxylation of phenol to catechol (confirmed by HPLC), substrate-dependent NADPH oxidation, absorption spectrum typical of flavoproteins and peptide mass fingerprint corresponding to flavoprotein hydroxylase. The enzyme utilizes phenol with apparent Michealis constant (Km) of 1.71 µM, maximal velocity (Vmax) of 0.4 µM/min with optimal activity at pH 7 and 35°C. Fe2+chelators (Phenanthroline and sodium arsenate), heavy metals, denaturants and oxidizing agents showed inhibitory effect on phenol hydroxylation activity of the enzyme. The enzyme has broad substrate specificity against isomeric diphenols, isomeric methylphenols, halogen-substituted phenols, amino-substituted phenols, nitrophenols, hydroxybenzaldehyde and hydroxylbenzoic acid. The enzyme shows remarkable storage stability at room temperature and at 4°C. The multisubstrate specificity coupled to remarkable storage stability of the microalgal phenol hydroxylase opens up avenues for its application in remediation of a wide range of phenolics released in industrial wastewater or phenolic biosensor application.

Phase‐controlled growth of cubic phase CuO nanoparticles by chemical vapor deposition

Cupric oxide has three polymorphs, namely, monoclinic, tetragonal, and cubic phases. The synthesis of the monoclinic phase is widely reported due to its versatile applications. However, cupric oxides with tetragonal and cubic structures were seldom investigated in the literature. In this study, the cubic phase of CuO was deposited on alumina substrate using Cu(acac)2 as precursor. The obtained CuO with loadings of 0.2–2 mmol g−1 on alumina was determined to be pure cubic phase by XRD and XPS, which is the first report on the synthesis of pure cubic phase, to the best of our knowledge. In contrast, pure monoclinic phase was obtained when impregnation method was employed. The cubic CuO nanoparticles obtained in this work appear to be highly dispersed with a particle size of around 5 nm. Moreover, the cubic CuO showed a lower chemical state and a lower reducibility as compared to monoclinic CuO supported on the same substrate. Further studies showed that the cubic phase was a metastable phase in thermodynamics and could be converted to monoclinic phase at elevated temperatures. As catalysts, the cubic CuO on alumina was found to be active and selective in the hydroxylation of phenol to catechol, hydroquinone and benzoquinone.

Catalytic Activity of Fe-SBA-15 Prepared by Evaporation-Induced Self-Assembly (EISA) Method

Fe-SBA-15 materials with different Fe content have been prepared using tetraethyl orthosilicate (TEOS) and iron nitrate (Fe (NO3)3·H2O as precursors and Pluronic P123 as structure directing agent through evaporation-induced self-assembly (EISA) method. The materials were characterized by nitrogen sorption, powder X-ray diffraction and TEM. All the Fe-SBA-15 samples appeared ordered 2D hexagonal mesostructure. The BET surface area and pore diameter were about 500 m2/g and 4 nm respectively. In the reaction of phenol hydroxylation to dihydroxybenzenes, the Fe-SBA-15 materials showed good catalytic activity, giving 20.2% of phenol conversion, 58.2% of selectivity for o-dihydroxy benzene and 41.8% of selectivity for p-dihydroxy benzene. After five cycles, the product yield was 25.2%, while selectivities of o-dihydroxy benzene and p-dihydroxy benzene were 58.2% and 41.8%, respectively. All these findings indicated the potential of Fe-SBA-15-10 could be used as a cost-effective, environment-friendly catalyst.

Comparison of Fe/HBEA catalysts from incipient wetness impregnation with various loading on phenol hydroxylation

Iron catalysts on zeolite beta from incipient wetness impregnation, Fe/HBEA with Fe loading 0.5–2.0 wt% were prepared and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic absorption spectroscopy (AAS), and temperature-programmed desorption of ammonia (NH3-TPD). Fe in all catalysts was in the form of Fe2O3 and the acidity decreased with an increase of Fe content. From catalytic testing in phenol hydroxylation, the catalysts with lower Fe loading gave higher yields of catechol and hydroquinone and a lower amount of by-products than the catalyst with Fe loading 6.0 wt% in the previous work. The spent catalysts were analyzed by temperature-programmed oxidation using thermogravimetric analysis/mass spectrometry detector (TGA-MS). An amount of carbon deposit from all catalysts was in the range 10–15 wt%. However, carbon on the catalysts with lower Fe loading was removed at higher temperature.

Preparation of TiO2-SiO2 via sol-gel method: Effect of Silica precursor on Catalytic and Photocatalytic properties

TiO2-SiO2have been synthesized by the sol-gel method from titanium isopropoxide and varied silica precursors: tetraethyl orthosilicate and tetra methyl ortho silicate. To study the effect of the precursor, prepared materials were characterized by X-ray diffraction, scanning electron microscopy, Diffuse Reflectance UV-vis optical absorption, and also gas sorption analysis. XRD patterns showed the formation of TiO2 anatase in the TiO2-SiO2 composite with different crystallite size from different silica precursor as well as the different surface morphology. The DRUV-vis absorption spectra exhibit similar band gap energy correspond to 3.21eV value while the surface area, pore volume and pore radius of the materials seems to be affected by the precursor. The higher specific surface area contributes to give the enhanced activity in phenol hydroxylation and methylene blue photodegradation.

Influences of M–Sn intermetallics (M = Ni, Cu) prepared by mechanical alloying on phenol hydroxylation

This work discusses the effect of the crystal structure of Ni–Sn and Cu–Sn intermetallic catalysts on phenol hydroxylation.

Hydrophilicity/hydrophobicity modulated synthesis of nano-crystalline and hierarchically structured TS-1 zeolites

Nanosized crystals and hierarchically structured materials are considered to be two important options to enhance the mass transportation efficiency in microporous zeolites. Herein, we first present a highly efficient gel-crystallization approach for the synthesis of TS-1 nanocrystals with an exceptionally high mass yield of up to 97.4% and a volume yield of ∼0.36 g ml−1. The resultant TS-1 nanozeolites (un-TS-1) possess uniform and tunable particle sizes from 80 nm to 2.0 μm. Compared to the TS-1 counterparts (ht-TS-1) synthesized by a direct hydrothermal method, the obtained un-TS-1 materials showed comparable or improved catalytic performance for epoxidation of 1-hexene and hydroxylation of phenol with dilute H2O2 as the oxidant. More importantly, a surface-hydrophilicity/hydrophobicity-modulated mechanism has been proposed to illustrate the distinct structural evolution pathway of un-TS-1 nanocrystals and single-crystalline ZSM-5 HSZs under identical synthetic conditions: the relatively stronger hydrophobicity of TS-1 due to the equal-valence substitution of Ti for Si, is suggested to be responsible for the formation of nanocrystalline TS-1, in comparison with ZSM-5 HSZs of higher hydrophilicity resulting from the tri-valence Al substitution for Si. The successful syntheses of relatively hydrophilic Al-containing TS-1 and Fe-doped silicalite-1 HSZs offer further support to this mechanism.

Ferrocene particles incorporated into Zr-based metal–organic frameworks for selective phenol hydroxylation to dihydroxybenzenes

Ferrocene@UiO-66 exhibited high catalytic activity for phenol hydroxylation with H2O2 at room temperature in water.

Effect of calcination temperature on the structure and catalytic performance of copper–ceria mixed oxide catalysts in phenol hydroxylation

We report on highly active CuO@CeO2 catalysts prepared by the surfactant-template method and calcined at different temperatures.

Enhanced catalytic activity towards one-pot hydroxylation of phenol with hydrogen peroxide by nickel(II) complex encompassing 3-formylchromone-S-methylisothiosemicarbazone derivatives

The new template reaction between 3-formylchromone-S-methylisothiosemicarbazone and substituted 2-hydroxy benzaldehydes in presence of Ni(OAc)2·4H2O salts afforded four new complexes (1–4) with general molecular formula [NiL1–4] (L1=(N1-3-formylchromone)(N2-(2-hydroxybenzylidene)-S-methylisothiosemicarbazone, L2=(N1-3-formylchromone)(N2-(2-hydroxy-1-naphthalene)-S-methylisothiosemicarbazone, L3=(N1-3-formylchromone)(N2-(5-chloro-2-hydroxybenzylidene)-S-methylisothiosemicarbazone, L4=(N1-3-formylchromone)(N2-(2-hydroxy-3-methoxybenzylidene)-S-methylisothiosemicarbazone). The compounds are remarkably stable and were obtained in good yields. Structural elucidation was carried out thoroughly in solid and solution-states by elemental analysis and various spectroscopy techniques (IR, UV–Vis, 1H NMR) as well as ESI-mass spectrometry. The molecular structure of the complex 1 was investigated by single-crystal X-ray diffraction. The analysis showed tetradentate coordination of the complexes 1–4, in which the metal atom adopts a square planar geometry with the ligand coordinating ONNO tetradentate fashion and the complex 1 [NiL1] units are forming dimerized chains through Ni(1)⋯Ni(2) interactions (3.408Å). The new complexes were examined for their catalytic performances in one-pot hydroxylation of phenol in presence of H2O2 into catechol and hydroquinone.

Preparation of 5,10,15,20-(4-hydroxy)phenylporphyrin copper/γ-Al2O3 and its performance as catalyst in phenol hydroxylation

A series of 5,10,15,20-(4-hydroxy)phenylporphyrin copper/γ-Al2O3 catalysts were prepared by impregnation and their structures were well characterized by means of 1H NMR, FT-IR, UV–Vis, ICP and nitrogen physisorption measurements. The characterization results demonstrated that CuTHPP was physically adsorbed on the surface of γ-Al2O3. With the hydroxylation of phenol as a model reaction, the effect of reaction conditions on hydroxylation activity of CuTHPP/γ-Al2O3 catalysts were investigated. The results showed that at a suitable condition, the conversion of phenol could reach to 36.8%, with the ratio of catechol to hydroquinone being 7.3:1. The reusability of catalyst illustrated that it could be recovered and reused without notable loss of activity.

Enhanced Catalytic Activity on Post‐Synthesized Hollow Titanium Silicalite‐1 with High Titanium Content on the External Surface

AbstractA titanium silicalite‐1 (TS‐1) extrudate with high content of titanium on the external surface was post‐synthesized by using the mixed solution of tetrapropylammonium hydroxide and the hydrolysate of tetrabutyl titanate. The influence of Ti concentration in the post‐synthesis solution on the physicochemical properties and catalytic performance of TS‐1 was also studied. The amorphous silica support covering on the external surface of TS‐1 was crystallized, and some hollows appeared in the samples that were post‐synthesized. Most titanium introduced by this method are located at the external surface of the new generated TS‐1 particles. The molar ratio of Si/Ti on the external surface decreases with the increase of the Ti concentration in the post‐synthesis solution. The catalytic activity for phenol hydroxylation over the TS‐1 samples is enhanced after the post‐synthesis due to the new generated framework Ti on the external surface, providing the reactants more easily adsorbable active centers. A proper Ti concentration (10 vol%) in the post‐synthesis solution leads to the highest catalytic activity by obtaining a proper ratio of tetrahedral and octahedral Ti to anatase TiO2.

Hydroxylation of Phenol over M-MCM-48

<p>The synthesis and characterization of M-MCM-48 (M= Si, Ti, V, Cr and Mn) materials have been carried out. These systems promote hydroxylation of phenol with 30 % H<sub>2</sub>O<sub>2</sub> and the hydroxylation activity is highest for Ti-MCM-48. Water appears to be a better solvent than acetone and acetonitrile.</p>

Regeneration of Deactivated Hollow Titanium Silicalite Zeolite from Commercial Ammoximation Process by Encapsulating Amorphous TiO2-SiO2Nanoparticles inside Zeolite Crystal

An efficient regeneration method to encapsulate the poisonous amorphous TiO2-SiO2 nanoparticles within zeolite crystal via post-synthesis has been developed. It is demonstrated that the encapsulation of Ti-rich nanoparticles can reduce the accessibility of H2O2 molecules to acid sites of Ti-rich nanoparticles, thus lowering the inefficient decomposition of H2O2 oxidant during catalytic reactions. Furthermore, the regenerated HTS zeolite is of smaller particle size than conventional TS-1 zeolite due to the existence of deactivated HTS as crystal seed during hydrothermal synthesis. Consequently, the regenerated HTS zeolite shows as high catalytic performance as fresh TS-1 zeolite in phenol hydroxylation reaction with 30 wt% H2O2 aqueous solution as oxidant. Importantly, this study exploits a novel concept on updating the lifetime of industrial zeolite catalyst, which is of both academic and practical significance.

Zeolite-Y encapsulated metal complexes of cobalt(II) as catalyst for the hydroxylation of phenol

The hydroxylation of phenol was investigated using cobalt(II) complexes of bidentate ligands including N,N′-ethylenebis(salicylideneamine)(salen), N,N′-propylenbis(salicylideneamine)(salpn) and N,N′-phenylenebis(salicylideneamine)(salophen) encapsulated in zeolite-Y. The catalysts were characterized by Fourier transform infrared and X-ray diffraction analyses to confirm the complex encapsulation. These complexes catalyze the liquid-phase hydroxylation of phenol, through H2O2, to catechol and hydroquinone as major and minor products, respectively. The activities of all prepared catalysts were tested for the oxidation of phenol and hydrogen peroxide. The overall reaction conditions were optimized to get maximum hydroxylation gain to consider the concentration of substrate and oxidant, amount of catalyst, and the reaction temperature. The zeolite encapsulated complexes of cobalt(II) were found to be catalytically active toward the hydroxilation of phenol. Under the optimized reaction conditions, [Co-(salen)]-Y showed the highest conversion, about 43 %, after 6 h which was followed by [Co-(salpn)]-Y with 39 % conversion and [Co-(salophen)]-Y showing the lowest efficiency with 35 % conversion. The hydroxylation of phenol without catalyst and with Co/zeolite-Y catalyst showed poor results.

A simple route to CuxSn(100−x) intermetallic nanoparticle catalyst for ultra-phenol hydroxylation

A practical methodology and novel, economical materials were proposed to successfully prepare nanoparticle catalysts for phenol hydroxylation. The preparation was carried out via mechanical alloying (MA) of CuxSn(100−x) powder mixtures (where x = 30, 50, 70, and 100%wt). The mechanical alloyed nanoparticles were characterized using various techniques. X-ray diffraction patterns indicated that η-Cu6Sn5, ε-Cu3Sn, and CuSn phases could be formed in the mechanical alloyed CuxSn(100−x) materials. Transmission electron micrographs and selected area electron diffraction patterns confirmed the presence of η-Cu6Sn5, ε-Cu3Sn, and CuSn phases. Activity of the catalysts, using the optimal conditions of 70 °C reaction temperature for 1 h, 50 mg of Cu0.5Sn0.5, and 1:3 phenol:H2O2 ratio, provided more than 98% conversion with 70% catechol (CAT) and 29% hydroquinone (HQ). Experimental results suggested that the presence of the ε-Cu3Sn phase gave higher activity while Sn reduced benzoquinone (BQ) to HQ. The catalyst maintained its stability with no structural collapse for more than 24 h.

Hydroxylation of phenol over MeAPO molecular sieves synthesized by vapor phase transport

In this study, MeAPO-25 (Me = Fe, Cu, Mn) molecular sieves were first synthesized by a vapor phase transport method using tetramethyl guanidine as the template and applied to hydroxylation of phenol. The zeolites were characterized by XRD, SEM, FT-IR, and DR UV–Vis. As a result, MeAPO-21 and MeAPO-15 were synthesized by changing the Me/Al ratio. UV–Visible diffuse reflectance study suggested incorporation of heteroatoms into the framework and FT-IR study also supported these data. Effects of heteroatoms, contents of Me in MeAPO-25, reaction temperature, phenol/H2O2 mole ratios, reaction time and concentration of catalyst on the conversion of phenol, as well as on the selectivity were studied. FeAPO-25 exhibited a high catalytic activity at the mole ratio of FeO and Al2O3 equal to 0.1 in the synthesis gel, giving the phenol conversion of 88.75% and diphenols selectivity of 66.23% at 60°C within 3 h [n(phenol)/n(H2O2) = 0.75, m(FeAPO-25)/m(phenol) = 7.5%]. Experimental results indicated that the FeAPO-25 molecular sieve was a fairly promising candidate for the application in hydroxylation of phenol.

A Facile Method for the Direct Introduction of FeOxin Mesoporous AMS Through A Templating Route (S−[MN]+I−) and Its Catalytic Application

A facile method has been developed to incorporate FeOx into the channels of anionic surfactant-templated mesoporous silica (AMS). This synthesized method was based on a novel templating route (S−[MN]+I−), in which Sar-Na (N-Lauroylsarcosine sodium) was employed as structure-directing agent (S−), Fe ion functionalized APATES (N-[3-(Trimethoxysilyl)propyl]ethylenediamine) as co-structure directing agent ([MN]+). The Fe ion functionalized APATES (Fe[APATES]+) could establish a critical interaction between the surfactant head group and silica species by counterion-mediated interaction during the synthesis process. The synthesized samples were characterized with XRD, N2 adsorption, XPS, FT-IR, UV-vis, H2-TPR, TEM. The results revealed that FeOx species could be highly dispersed onto the pore channel surface and have a strong interaction with the silica wall. Furthermore, this catalyst of FeOx-AMS exhibited high catalytic performances for the hydroxylation of phenol.

Preparation of large pore volume γ-alumina and its performance as catalyst support in phenol hydroxylation

Alumina was synthesized from Al(NO3)3, AlCl3 and Al3(SO4)2 with NaOH, and from NaAlO2 with HNO3 by addition of acidic solution to alkaline solution with a syringe pump. The as-produced Al2O3 precursors were supercritically dried and calcined at 500 °C to obtain mesoporous γ-alumina material. Results showed that all the inorganic aluminum salts could be used to synthesize high pore volume γ-alumina by controlling the precursor addition rate at room temperature and supercritical CO2 drying. However, the γ-alumina with the largest pore volume (5.4 cm3/g), BET surface area (423.7 m2/g) and pore size (37.8 nm) was obtained using Al(NO3)3 and NaOH. This γ-alumina was further used as a support for Fe-based catalyst with hydrogen peroxide to produce hydroquinone and catechol in the phenol hydroxylation reaction in 30 min at 80 °C. The conversion of phenol was 53.4% whereas the selectivity to dihydroxybenzenes-DHBs (hydroquinone-HQ and catechol-CAT) was as high as 96.2%, revealing that the larger pore volume takes effect in the γ-alumina as support for the Fe-based catalyst in the hydroxylation reaction, and that the γ-alumina may be a good candidate as the support for other important catalysts such as those used in the petroleum refining industry.

Irreversible deactivation of hollow TS-1 zeolite caused by the formation of acidic amorphous TiO2–SiO2 nanoparticles in a commercial cyclohexanone ammoximation process

Commercial deactivated HTS zeolite has been investigated by multiple characterization methods and catalytic evaluations. These indicate that structural and textural properties are not mainly ascribed to the irreversible deactivation, but some framework Ti species are transformed into Ti-rich nanoparticles. Both Brønsted and Lewis acid sites are observed in deactivated HTS zeolite, which agrees well with the spectroscopic characterization results and Tanabe’s acidity theory on mixed binary oxides. Hence the acidic Ti-rich aggregates are attributed to the amorphous TiO2–SiO2 nanoparticles located on the external surface of the zeolite. Furthermore, it is demonstrated that the catalytic performance of deactivated HTS zeolite in phenol hydroxylation is seriously dependent on its acidity properties, which can accelerate the decomposition of H2O2. As a consequence, we conclude that the irreversible deactivation of HTS zeolite in the ammoximation process is caused by the formation of acidic amorphous TiO2–SiO2 nanoparticles catalyzing the fast H2O2 decomposition reaction.