Hydroxylation Of Phenol Research Articles

Enhanced Activity and Selectivity in the One-Pot Hydroxylation of Phenol by Pd/SiO2@Fe-Containing Mesoporous Silica Core–Shell Catalyst

A novel approach to enhance the catalytic performances in one-pot hydroxylation of phenol into catechol and hydroquinone was examined using core–shell type catalysts which consist of Pd nanoparticles (NPs) for direct synthesis of H2O2 from H2 and O2 and Fe-containing mesoporous silica (Fe-MS) for hydroxylation of phenol using in situ produced H2O2. We have newly prepared three types of core–shell catalysts: (i) Pd/SiO2 core covered with Fe-MS (Pd/SiO2@Fe-MS), (ii) SiO2 core covered by Fe-MS with randomly distributed Pd NPs within the mesoporous silica structure (SiO2@Pd(R)/Fe-MS), where (R) indicates random, and (iii) SiO2 core covered by Fe-MS with Pd NPs deposited on the outer surface of the mesopores SiO2@Pd(S)/Fe-MS, where (S) indicates the surface. The effects of the relative position between the Pd NPs and Fe-MS on the catalytic activity and the selectivity were investigated. As a result, it was clearly demonstrated that the relative position significantly affects not only the reaction rate but also the product selectivity, and the Pd/SiO2@Fe-MS showed the best performance among them. The applicability of the Pd/SiO2@Fe-MS is also demonstrated in the one-pot oxidation of adamantine. The present design strategy offers a very simple and efficient methodology to realize a one-pot reaction.

Insights into membrane fouling of a side-stream ceramic membrane reactor for phenol hydroxylation over ultrafine TS-1

A side-stream ceramic membrane reactor was established for continuous phenol hydroxylation to dihydroxybenzene including catechol and hydroquinone over ultrafine titanium silicalites-1 (TS-1) catalysts with H2O2 as the oxidant. The membrane fouling mechanisms were investigated in detail by designing a series of filtration experiments based on the gas chromatography/mass spectrometry (GC/MS) analysis of the reaction mixtures. The field emission scanning electron microscopy (FESEM) and energy-dispersive X-ray spectroscopy (EDS) were used to reveal the surface morphology and chemical nature of the fouled membranes. It is found that the reactant (phenol) and the target products (catechol and hydroquinone) have little influence on membrane fouling, but the overoxidation by-products of target products, such as p-benzoquinone, play an important role in membrane fouling. The filter cake formed on the membrane surface composed of the TS-1 particles and the overoxidation by-products is the main reason of membrane fouling. An efficient cleaning strategy of fouled membrane was also proposed, which leads to an over 95% recovery of pure water flux of the fouled membranes.

Oxidative Coupling and Hydroxylation of Phenol over Transition Metal and Acidic Zeolites: Insights into Catalyst Function

Reaction of phenol with hydrogen peroxide over H-MFI, Fe-MFI, H-BEA, Fe-BEA and TS-1 zeolite catalysts was investigated. Over H-BEA, biphenyl product was observed. It is suggested, that the larger pore size of H-BEA facilitates coupling of two phenol molecules. Two distinct reaction mechanisms are proposed for acid and redox catalysts.

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.

Titanium species in deactivated HTS-1 zeolite from industrial cyclohexanone ammoxidation process

The types of titanium species and contents in commercialized hollow titanium silicalite (HTS-1) zeolite are essentially related to their ammoxidation performance. XRD and combined TEM methods were used in this study to identify the titanium species in the deactivated HTS-1 zeolite discharged from cyclohexanone ammoxidation unit. Core–shell structure of crystalline–amorphous TiO2 was observed for the first time in the deactivated HTS-1 zeolite. The results of their catalytic activities in phenol hydroxylation are in line with the analysis. This study provided valuable information to understand the deactivation mechanism of HTS-1 zeolite in cyclohexanone ammoxidation.

Iron Incorporated Mesoporous Molecular Sieves Synthesized by a Microwave-Hydrothermal Process and Their Application in Catalytic Oxidation

Fe-FSM-16 and Fe-containing mesoporous materials (Fe-JLU-15) prepared by using semifluorinated surfactant as a template, have been synthesized by microwave-hydrothermal (M-H) process and characterized by several spectroscopic techniques. The catalytic activity of these materials was tested for the phenol hydroxylation and wet phenol oxidation with H2O2 under mild reaction conditions. The effect of pH, H2O2/PhOH molar ratio and stability of the catalyst on the oxidation process was also investigated. Phenol oxidation and H2O2 decomposition show that the Fe-JLU-15 is more active than Fe-FSM-16 and more stable in aqueous solution. The total amount of dissolved iron is less than 5 wt% of the iron initially contained in the catalyst. In phenol hydroxylation, these two solids can effectively catalyze the phenol hydroxylation. Catechol and hydroquinone were observed as the major products, with a difference in the product distribution for these solids. The Fe-JLU-15 has a high selectivity for catechol (63.5 % phenol conversion, CAT/HQ = 2.7) while the Fe-FSM-16 shows a high selectivity for hydroquinone (56.8 % phenol conversion, CAT/HQ < 1) under the same reaction conditions.

Synthesis of mesoporous iron-incorporated silica-pillared clay and catalytic performance for phenol hydroxylation

Fe-incorporated silica-pillared clays (Fe-SPCs) with ordered interlayer mesoporous structure have been synthesized through a new two-step procedure including the modification of the silica nano-pillars with potassium ferricyanide (K3Fe(CN)6) and successive calcination. X-ray diffraction, nitrogen adsorption–desorption, Fourier transform infrared spectra, X-ray fluorescence analyses, diffuse reflectance UV–vis spectra and X-ray absorption near-edge structure spectra were used to characterize the structures and the synthesizing mechanism of Fe-SPCs. Results show that all iron species were tetrahedrally coordinated with the interlayer silica nano-pillars, and the cationic surfactant molecule plays an important role in the intercalation of tetraethoxysilane and the introduction of iron into the intragallery silica framework. Moreover, the structural parameters of Fe-SPC can be adjusted by controlling the concentration of K3Fe(CN)6, as the concentration of K3Fe(CN)6 increases from 1M to 2M, the gallery height of Fe-SPC increases from 2.51 to 2.66nm, while the Brunauer–Emmett–Teller (BET) surface area, pore volume and Barrett–Joyner–Halenda (BJH) pore size decrease from 856 to 794m2/g, 0.75 to 0.69cm3/g, and 2.2 to 2.0nm, respectively. The Fe-SPCs show good catalytic activity in phenol hydroxylation using H2O2 as oxidant (phenol:H2O2=1:1, water), specifically, the phenol conversion is 46.2%, and the selectivity of dihydroxybenzenes is 70.6% at 343K.

Synthesis, Characterization And Catalytic Activity Of Transition Metal Complexes Of Ascorbic Acid Encapsulated In Fly Ash Based Zeolite

A new route for the utilization of fly ash has been formulated. X-type zeolite has been synthesized from fly ash by alkali fusion followed by hydrothermal treatment. Ascorbic acid was used as a ligand for the synthesis of metal complexes of copper, nickel and vanadium encapsulated in the super cages of fly ash based zeolite (FAZ) by flexible ligand method and characterized by FTIR, XRD, Atomic Absorption Spectrometry (AAS), Ultra Violet–Visible spectroscopy and Thermo gravimetric analysis (TGA). The additional peaks corresponding to that of the complex have been observed which confirms the loading of the metal complexes in the zeolite cavities. The shifting of C=C-O stretching frequency found at 682 cm -1 in ascorbic acid to 601 cm -1 confirms the co-ordination of the ligand resulting in the formation of the metal complex. The thermo grams show deflation in three regions corresponding to the loss of the intra-zeolite water, metal complexes and the structural –OH group respectively. The catalytic activity of these complexes towards the liquid phase hydroxylation of phenol with hydrogen peroxide has been established. The extent of the reaction as a function of time has been investigated. Vanadium-ascorbate complex had the highest conversion of 78%. The product was identified as hydroquinol by GC-MS. This study reports a highly attractive catalytic method for the preparation of hydroquinol from phenol using aqueous hydrogen peroxide as the oxidising agent which is industrially significant.

Phenol hydroxylation over Fe-incorporated mesoporous materials prepared by coprecipitation

Mesoporous iron-incorporated materials were prepared by coprecipitation method and used as catalyst for the hydroxylation of phenol. Several techniques, including ICP-AES, XRD, FT-IR, UV–vis, BET, TPR and XPS, were used to characterize the structural properties of these materials. The results indicated that iron atoms incorporated into the mesoporous silica framework of tetrahedral coordination environment forming a new type of active sites. With the increase of iron content, part of iron atoms deposited on extraframework. Framework iron atoms were found to be beneficial to phenol hydroxylation, while extraframework small oligometric iron species accelerated the deep oxidation of dihydroxybenzenes producing tar. Under the optimized conditions, a phenol conversion of 47.3% with the yield of 45.7% and selectivity of 96.6% to dihydroxybenzenes was obtained. The leaching of extraframework iron atoms and the blocking of active sites by tar formed led to the gradual attenuation of activity. Tar adsorbed on the catalyst could be burnt up by calcinations making the catalyst regenerated. A stable yield of about 30% to dihydroxybenzenes could be obtained.

Formation mechanism and catalytic application of hierarchical structured FeAlPO-5 molecular sieve by microwave-assisted ionothermal synthesis

At atmospheric pressure, FeAlPO-5 molecular sieve with hierarchical micro- and meso-porous structure has been ionothermally synthesized by microwave heating with eutectic mixture as the solvent. Among the synthesis parameters investigated, the ratio of P2O5/Al2O3, aluminum source, and heating methods significantly affected the mesoporosity of FeAlPO-5 molecular sieve. N2 Physisorption, SEM and TEM characterizations showed that the resultant material possessed inter- and intra-crystalline mesopores simultaneously. The larger intercrystalline mesopores in size resulted from the intercrystalline void space between bar crystals and nanoparticles. The calcination removed the organic species embedded in the crystals of FeAlPO-5 molecular sieve, leading to the formation of smaller intracrystalline mesopores. The catalytic properties of hierarchical FeAlPO-5 molecular sieve were investigated in the hydroxylation of phenol with microporous FeAlPO-5 as a reference. The results showed that the catalytic performance of the former catalyst was superior to the latter.

Design of a bio-inspired copper (II) Schiff base complex grafted in mesoporous silica for catalytic oxidation

Controlled grafting of a copper (II) complex with a Schiff base ligand (LA=N-(salicylaldimine)-(N′-propyltrimethoxysilane)-diethylenetriamine) on a mesoporous MCM-41 type of silica (LUS) was accomplished using a pattering technique to allow a homogeneous distribution of isolated copper sites on the solid using trimethylsilyl groups as dispersing function. XRD patterns suggest that the final material LUS-CuLA exhibits a well-ordered 2D hexagonal structure. Elemental analysis, solid UV–Vis and EPR spectroscopies indicate that the copper (II) coordination sphere is most likely of a 3N1O type with an additional acetate ion as a ligand. Almost all the Cu(II) species grafted on the solid were EPR active (2.6wt% active species for 2.8wt% total copper measured from ICP-MS analysis) confirming the presence of monomeric copper species. Preliminary catalytic tests for phenol hydroxylation show that the supported system presents similar activity as the molecular analogue.

Evaluation of Iron-Containing Aluminophosphate Molecular Sieve Catalysts Prepared by Different Methods for Phenol Hydroxylation

Three iron-containing AlPO4-5 molecular sieve catalysts (i.e. FeAlPO-5-Iono, FeAlPO-5-Hydro and FeAlPO-5-Imp) were prepared by ionothermal synthesis, direct hydrothermal synthesis and impregnation method, and characterized by various techniques. N2 adsorption/desorption measurements, together with the results of SEM and TEM, showed that FeAlPO-5-Iono was a new type of aluminophosphate molecular sieve with hierarchical micro- and meso-porous structure, whereas both FeAlPO-5-Hydro and FeAlPO-5-Imp were typical microporous materials. DR UV–Vis analysis suggested that the order of the amounts of isolated Fe3+ species in these three samples was as follows: FeAlPO-5-Hydro > FeAlPO-5-Iono > FeAlPO-5-Imp. However, the order of their catalytic performances towards phenol hydroxylation was in opposition to that of the amounts of isolated Fe3+ species. Detailed analysis revealed that it was textural properties of these catalysts that determined phenol conversion and dihydroxylbenzene selectivity. The catalyst-recycling tests suggested that extra-framework iron clusters were readily leached into the reaction system and had great influence on the hydroxylation of phenol. Due to the sole presence of isolated Fe3+ species and enhanced mass transport of reactants and products to/from these active sites, FeAlPO-5-Hydro was found to have the best reusability among these catalysts. .

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.

Catalytic Phenol Hydroxylation with Dioxygen: Extension of the Tyrosinase Mechanism beyond the Protein Matrix

A new catalyst (see structure) hydroxylates phenols with O2 via a stable side-on peroxide complex, which is similar to the active site of tyrosinase in terms of the ligand environment and its spectroscopic properties. The catalytic oxidation of phenols to quinones proceeds at room temperature in the presence of NEt3 and even non-native substrates can be oxidized catalytically. The reaction mechanism is analogous to that of the enzyme-catalyzed reaction.

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.

Bacterial pyridine hydroxylation is ubiquitous in environment

Ten phenol-degrading bacterial strains were isolated from three geographically distant environments. Five of them, identified as Diaphorobacter, Acidovorax, Acinetobacter (two strains), and Corynebacterium, could additionally transform pyridine, through the transcription of phenol hydroxylase genes induced both by phenol and pyridine. HPLC-UV and LC-MS analyses indicated that one metabolite (m/e = 96.07) with the same molecular weight as monohydroxylated pyridine was produced from the five phenol-degrading strains, when pyridine was the sole carbon source. Phenol (50 mg l(-1)) could initially inhibit and later stimulate the pyridine transformation. In addition, heterologous expression of the phenol hydroxylase gene (pheKLMNOP) resulted in the detection of monohydroxylated pyridine, which confirmed the phenol hydroxylase could catalyze pyridine hydroxylation. Phylogeny of the phenol hydroxylase genes revealed that the genes from the five pyridine-hydroxylating strains form a clade with each other and with those catalyzing the hydroxylation of phenol, BTEX (acronym of benzene, toluene, ethylbenzene, and xylene), and trichloroethylene. These results suggest that pyridine transformation via hydroxylation by phenol hydroxylase may be prevalent in environments than expected.

Ceramic hollow fiber membrane distributor for heterogeneous catalysis: Effects of membrane structure and operating conditions

A ceramic hollow fiber membrane distributor was proposed for the micro-scale distribution of reactants in heterogeneous catalytic reaction. To evaluate the feasibility and the performance of the ceramic hollow fiber membrane based reactant distribution, phenol hydroxylation with hydrogen peroxide (H2O2) over TS-1 solid catalysts was selected as a model reaction. The effects of membrane structural parameters of ceramic hollow fiber membrane on the micro-scale distribution and the reaction selectivity were studied in detail. The influence of operation conditions such as hydrogen peroxide flow rate, stirring rate and phenol/H2O2 molar ratio on the membrane distribution process was discussed. The ceramic hollow fiber membrane with small pore size and proper gradient in the pore structure was demonstrated to have a promotion effect on the reaction selectivity, which indicated its ability to generate uniform droplets in micro-scale. In addition, the increase of H2O2 flow rate and/or stirring rate can result in an improvement of reaction selectivity. Because of its controllable structure, high chemical stability and high packing density, the ceramic hollow fiber membrane distributor has potential for widespread applications in heterogenous catalysis.

Continuous phenol hydroxylation over ultrafine TS-1 in a side-stream ceramic membrane reactor

A side-stream ceramic membrane reactor system was developed that can facilitate the in situ separation of ultrafine catalysts from the reaction mixture and make the production process continuous. Continuous hydroxylation of phenol to dihydroxybenzene over ultrafine titanium silicalites-1 (TS-1) was taken as a model reaction to evaluate the feasibility and performance of the membrane reactor system. The effects of membrane pore size and operation conditions (residence time, temperature, catalyst concentration, phenol/H2O2 molar ratio) on the performance of the reactor system were examined via single factor experiments. We demonstrated that the membrane pore size and operation conditions greatly affect the conversion, selectivity and filtration resistance. The phenol conversion and dihydroxybenzene selectivity remain stable at about 11% and 95% in a 20-h continuous run, respectively.

Benzene Hydroxylation and Simultaneous Extraction of Phenol in Two Membrane Contactors Made with Three-Compartment Cells

Two different three-compartment membrane contactors [called solid membrane contactor (SMC) and liquid membrane contactor (LMC)] were tested in the synthesis and separation of phenol produced by direct hydroxylation of benzene using a Fenton reaction. Phenol produced in the aqueous reacting phase was extracted in the organic phase and simultaneously stripped in the basic aqueous phase. Preliminary tests on phenol recovery evidenced better performances (86.5% of phenol recovered in the strip phase) using the SMC with 0.1 M Na2SO4 in the aqueous feed phase at 35 °C. In the tests of partial oxidation, higher phenol productivity (0.62 gph gcat–1 h–1) was obtained in this last system because the high phenol flux away from the reacting phase permitted one to extract a high amount of phenol in the organic and aqueous (strip) phases. This extraction protected phenol by its subsequent oxidation. It was evidenced that the use of a third compartment containing an alkaline aqueous stripping phase permitted one to reco...

One-Step Synthesis of Nano-Size Iron Oxide /Three-Dimensional Wormlike Hierarchical Mesoporous SiO&lt;sub&gt;2&lt;/sub&gt; Catalysts and its Catalytic Performance on Phenol Hydroxylation

A series of nano-sized iron oxide supported on 3D wormlike hierarchical mesoporous SiO2 catalysts were synthesized by one-step hydrothermal synthesis. The samples were characterized by XRD, N2 sorption, FT-IR, UV–Vis, TEM and ICP-AES. The catalysts were probed for the oxidation of phenol employing hydrogen peroxide. The results indicate that the materials exhibit high surface area and 3D wormlike hierarchical pore, iron ions exist as isolated framework species when the weight percentage content of iron is below 0.24 and nano-size iron oxide is dispersed in the surface (iron content above 0.24 wt%). Catalytic performance indicates that nano-size iron oxide supported on SiO2 is useful to enhance both the catalytic activity and the selectivity of target products compared with isolated iron species.