Catalysts For Hydroxylation Of Phenol Research Articles

Diatomite as high performance and environmental friendly catalysts for phenol hydroxylation with H2O2

A series of diatomite catalysts were treated and characterized. For the first time, the resulting materials were used in catalysis for the hydroxylation of phenol with H2O2 and showed very high hydroxylation activity due to the Fe species in the diatomite. The effect of HCl treatment, contents of catalysts and H2O2 were investigated and the active components of diatomite were discussed. The results show that diatomite is the promising candidate for industrial output due to their high catalytic activity, easy physical separation and very low costs.

A novel silk fibroin‐supported iron catalyst for hydroxylation of phenol

AbstractThe aim of this study was to explore the potential use of silk fibroin (SF) as a catalyst support material for phenol hydroxylation reactions. Iron‐substituted silk fibroin fibers were prepared using formic acid at room temperature and characterized using inductively coupled plasma atomic‐emission spectrometry, scanning electron microscopy, Fourier transform infrared spectroscopy (FTIR) and optical microscopy. Measurement of an FTIR spectrum showed that the secondary structure was β‐structure before and after iron substitution. To evaluate the catalytic properties of prepared catalyst, phenol hydroxylation reaction was carried out using aqueous hydrogen peroxide as an oxidant. An excellent transformation of phenol into dihydroxybenzenes (catechol and hydroquinone) was achieved. Phenol conversions of 3.3%, 61.2%, and 80.3% were obtained at room temperature, 40 °C and 60 °C respectively. It was found that no further phenol conversion proceeded because catalysts became separated from the reaction system during the reaction. No significant leaching of the iron was detected. Catalyst could be reused several times without a significant change in activity. Parent silk fibroin fibers without iron were inactive. Copyright © 2006 Society of Chemical Industry

Rod‐Like Cu/La/O Nanoparticles as a Catalyst for Phenol Hydroxylation.

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CuO-containing MCM-48 as catalysts for phenol hydroxylation

The CuO–MCM-48 catalysts prepared by wet impregnation technique were originally used as the catalysts, with high phenol conversion and diphenol selectivity, for phenol hydroxylation with hydrogen peroxide. Furthermore, the optimized reaction conditions over these catalysts for phenol hydroxylation were acquired.

Deactivation and regeneration of TS-1/diatomite catalyst for hydroxylation of phenol in fixed-bed reactor

Abstract The performance of the TS-1/diatomite catalyst for hydroxylation of phenol was investigated in the fixed-bed reactor. The results show that the activity and the selectivity to product of the TS-1/diatomite catalyst decrease simultaneously with an increase of the reaction time, which indicates that the TS-1/diatomite catalyst has deactivated gradually during the reaction. The deactivated catalyst was characterized by XRD, UV–vis, FT-IR, N 2 adsorption and thermogravimetric analysis techniques. It was found that the crystallinity of TS-1/diatomite catalyst decreased slightly, but the structure of TS-1 zeolite and the content of titanium in the framework were unchanged. Compared with the fresh catalyst, the channels of the TS-1/diatomite catalyst were blocked by the organic byproducts, to result in the obvious decrease in the surface area and pore volume of the deactivated catalyst. The deposited byproducts inside the channels of TS-1/diatomite can be removed by calcining at 550 °C or refluxing with dilute hydrogen peroxide, which makes the performance of the deactivated catalyst recover completely.

Rod-like Cu/La/O nanoparticles as a catalyst for phenol hydroxylation

Rod-like La/Cu/O nanoparticles, synthesized by a simple coprecipitation reaction with a sonication process, are found to be highly active as a catalyst for the hydroxylation of phenol. Compared to the 4-6 h, 40% yield reported in the literature, our nanoparticle catalyst demonstrates a nearly 100% conversion within 4 h based on gas chromatography.

Cu- and Fe-ZSM-5 as catalysts for phenol hydroxylation

Cu- and Fe-ZSM-5 catalysts were hydrothermally synthesized and characterized by XRD, BET, FT-IR and UV–vis. The catalytic activity of several samples was tested for the aqueous hydroxylation of phenol with hydrogen peroxide. Two different mineralizing agents were used to prepare Cu-ZSM-5 catalysts: methylamine (Cu-Z-o) and sodium hydroxide (Cu-Z-B). Fe-ZSM-5 catalysts were synthesized either without mineralizing agent (Fe-Z-s) or with ammonium fluoride (Fe-Z-f). The metallic content of the synthesized materials varied between 0 and 1.8 wt.% and the Si/Al ratio varied from 32 to infinity. The type of mineralizing agent has a strong influence on the Cu or Fe species incorporated into ZSM-5. Cu I and Cu II predominated in Cu-ZSM-5 prepared with methylamine whereas Cu° clusters besides Cu I and Cu II were detected on Cu-Z-B. When copper and Al contents decreased in Cu-ZSM-5 catalysts catechol production was favored. Cathecol was also preferably obtained over low iron loaded ZSM-5 prepared with NH 4-F as mineralizing agent. Fe-Z-f samples contained both framework and extraframework iron species. The best reaction conditions found in this work to obtain high yields of catechol and hydroquinone are 1 mmol phenol, molar ratio phenol/H 2O 2 = 3, catalyst = 20 mg, T = 80 °C, water = 5 g, reaction time = 4 h.

Effect of pretreatment on properties of TS-1/diatomite catalyst for hydroxylation of phenol by H 2O 2 in fixed-bed reactor

The TS-1/diatomite catalyst was prepared for the hydroxylation of phenol with H 2O 2 in the fixed-bed reactor and the effects of pretreatment on the properties of TS-1/diatomite were studied by FT-IR, XRD, UV–vis, ICP-AES, BET surface area and NH 3-TPD techniques. It is shown when the catalyst is pretreated by the KAc, NaAc, NH 4Ac, NH 4Cl or HNO 3 aqueous solution, the framework structure of TS-1 is not destroyed and titanium in the framework is not removed. The surface area of catalyst has no obvious change compared with that of the untreated catalyst. But the extra-framework TiO 2 can be removed partly, which leads to the slight increase of the crystallinity of catalyst and the decrease of acid concentration on the surface of the TS-1/diatomite catalyst. As a result, the activity, selectivity and utilization of H 2O 2 for hydroxylation of phenol are improved. After the TS-1/diatomite catalyst is pretreated by the NH 3·H 2O, Na 2CO 3 or Na 3PO 4 solution, its framework silicon is dissolved partly in the base solution and the framework structure of TS-1 is destroyed. While the crystallinity and surface area of catalyst decrease and the concentration of acid sites on the surface of catalyst increased slightly. As a result, the catalytic activity of the TS-1/diatomite catalyst for hydroxylation of phenol descended or deactivated completely.

Cu2+-Exchanged Zeolites as Catalysts for Phenol Hydroxylation with Hydrogen Peroxide

The Cu2+-exchanged NaY, HY, USHY, Hβ, and HZSM-5 zeolites were prepared and evaluated in phenol hydroxylation with hydrogen peroxide using an atmospheric batch reactor. CuNaY, CuHY, and CuHβ catalysts were found to be more active than TS-1 or a simple homogeneous copper nitrate catalyst under similar reaction conditions. Both zeolite type and copper content in the zeolite catalyst were revealed to exert critical impact upon the catalytic activity in phenol hydroxylation. Reaction time, reaction temperature, and the molar ratio of phenol to hydrogen peroxide also remarkably influenced the reaction results. The addition of a small amount of hydrochloric acid to the reaction systems significantly enhanced the phenol conversion, hydroxylation selectivity, and reaction rate. The used catalysts can be regenerated completely by calcination at 450 °C for 4 h in air. On the basis of ESR spectroscopy, the relationship between catalytic activity and copper loading is explained and the hydroxyl radical is suggested a...

Fe-containing pillared clays as catalysts for phenol hydroxylation

An alternative method for the preparation of mixed Fe–Al-pillared clays (Fe–Al-PILCs) derived from two natural smectites, Wyoming SWy-1 and Tunisia-Gafsa VI (an iron-rich sample) based on the use of a mixture of FeCl 3 and chlorhydrol is described. The effect of the pH of the pillaring solution and the Al/Fe ratio are studied in order to assess their influence in the characteristics of the resulting solids: specific surface area, porosity and thermal stability. The behaviour of these solids as catalysts has been checked in the hydroxylation of phenol, under conventional heating or microwave irradiation, this last one allowing better yields and shorter reaction times. The presence of redox centers in the layers or in galleries of the materials, together with a Brönsted acid environment in the galleries of the PILCs, (mixed Fe–Al-PILCs and Al-PILCs derived from the Tunisian clay) induces the hydroxylation of phenol reaching conversions close to 70% under microwave irradiation, even at low reaction time (5 min). These values are comparable or even greater than conversions obtained from other catalysts used for these reactions (i.e. modified MCM).

Synthesis and Structure of Copper Hydroxyphosphate and Its High Catalytic Activity in Hydroxylation of Phenol by H2O2

A complex oxide of Cu2(OH)PO4 has been successfully synthesized by the hydrothermal method, and its structure was investigated by X-ray analysis. It crystallizes in the orthorhombic space group of Pnnm with a=8.058(2), b=8.393(2), and c=5.889(2) Å. Furthermore, the sample was characterized by thermal analysis (DTA and TG), and these results indicated that the sample was stable below 650°C. After calcination at 850°C, Cu2(OH)PO4 was dehydrated to form Cu4O(PO4)2. The sample isotherm for N2 showed that there wre no micropores or mesopores, and the surface area was only at 1.4 m2/g when the particle size of the sample was 150 μm. Moreover, when this sample was used as a catalyst for phenol hydroxylation by H2O2, the catalytic data showed high activity, which was comparable to that of TS-1. Various factors that influence this catalytic reaction, such as the solvent, reaction temperature, reaction time, catalyst size, catalyst amount, molar ratio of phenol to H2O2, and mode of H2O2 addition, were investigated intensively. Additionally, this catalytic reaction was characterized by electron spin resonance (ESR), and it was found that on the Cu2(OH)PO4 catalyst hydroxyl radicals possibly resulting from Cu2+ and H2O2 were important intermediates for formation of catechol and hydroquinone from hydroxylation phenol.

Novel Fe‐based complex oxide catalysts for hydroxylation of phenol

Novel catalysts for the hydroxylation of phenol, Fe–Si–O, Fe–Mg–O and Fe–Mg–Si–O complex oxides, have been synthesized by a coprecipitation method. X‐ray diffraction studies show that MgFe2O4 crystallites with spinel structure are formed in Fe–Mg–Si–O and Fe–Mg–O complex oxides and the crystallite size of the metal oxide or complex oxide is reduced after addition of Si. In the hydroxylation of phenol with hydrogen peroxide, Fe‐based complex oxides exhibit high activities after a short induction period. The phenol conversion is improved when silicon is introduced into the Fe‐based complex oxides, and formation of MgFe2O4 crystals with spinel structure in the catalysts increases the diphenol selectivity. The addition of a little acetic acid to the reaction liquid can shorten the induction period effectively. Under the same reaction conditions, phenol conversion and diphenol selectivity over the Fe–Mg–Si–O catalyst are close to those over TS‐1, and furthermore, the reaction time is more than ten times shorter as compared to TS‐1. The reaction mechanism of the hydroxylation of phenol on the catalysts has been studied, and a free‐radical mechanism initiated by the formation of phenoxy free radicals is suggested.

Highly effective Cu-HMS catalyst for hydroxylation of phenol

Transition metals copper and titanium substituted mesoporous silicas (Cu-HMS and Ti-HMS) were synthesized at ambient temperature by using dodecylamine (DDA) surfactant as templating agent. XRD measurements prove that incorporating titanium and especially copper into the mesostructures causes the d100 peaks of mesoporous silicas to become shifted to lower angles, indicating progressive expansion of the lattice d-spacings upon heteroatoms Ti and especially Cu incorporating. FT-IR measurements indicate that the calcined Cu-HMS and Ti-HMS samples all exhibit a weaker absorption band near 960 cm-1 which may be rather a fingerprint of the heteroatom on the matrix of [SiO4] units whatever its crystallization state. Cu-HMS possesses relatively high catalytic activity for the hydroxylation of phenol with 30% aq. H2O2 in aqueous solution (about 36% phenol conversion and more than 95% selectivity for dihydroxybenzene isomers), but Ti-HMS has no catalytic activity under the same reaction conditions. The product distribution obtained from Cu-HMS is completely different from that of the microporous titanium silicalite zeolites (TS zeolites). This is attributed to the porous structural differences between Cu-HMS and TS zeolites. The catalytic activity of the Cu-HMS is strongly dependent on the nature of the solvent; the Cu-HMS does not have any catalytic activity in the presence of organic solvents such as methanol or acetone instead of water. A reusing test of the recovered Cu-HMS indicates that the recovered catalyst suffers almost loss of activity and must be regenerated by calcination in air at 873 K in order to recover its activity.

Fe 2O 3/macroporous resin nanocomposites: Some novel highly efficient catalysts for hydroxylation of phenol with H 2O 2

A series of iron-oxide nanoparticles were prepared inside the pores of macroporous resins by in situ forced hydrolysis of Fe 3+ ions chemisorbed at the pore walls. The resulting composites were identified with transmission electron microscopy (TEM), UV-visible and near IR spectroscopy and surface photovoltage spectroscopy (SPS). The phase of the resulting iron-oxide particles embedded in resin was β-FeOOH. The particles ranged from 2 to 5 nm in size and were spherical in shape. These composites were used in catalysis for hydroxylation of phenol with H 2O 2. They showed very high hydroxylation activity due to nanosized β-FeOOH particles inside resins with very little aggregation and also showed easy physical separation due to the polymer matrix. In addition, the acidic environment around the β-FeOOH particles accelerated their hydroxylation activity.

Fe2O3/macroporous resin nanocomposites. High efficiency catalysts for hydroxylation of phenol with H2O2

Hydrated α-Fe2O3 nanoparticles were prepared inside resin pores byin situ forced hydrolysis of Fe3+ ions chemisorbed at the pore walls. They range from 20 to 50 A in size and are spherical in shape. They were used in catalysis for hydroxylation of phenol with H2O2 and possessed very high hydroxylation activity.