Direct Synthesis Of Phenol Research Articles

Photocatalytic property of WO3 modified with noble metal co-catalysts towards selective hydroxylation of benzene to phenol under visible light irradiation

Direct synthesis of phenol from benzene in the presence of water and oxygen were conducted under visible-light irradiation. Effects of several noble metal co-catalyst on the selective hydroxylation of benzene over WO3 photocatalysts have been extensively studied. The photocatalytic activities of WO3 for phenol formation strongly depend on co-catalyst such as Pt, Au, Pd metal species, i.e., phenol formation was as follows: Pt-WO3 > Au-WO3 > Pd-WO3. Furthermore, the WO3 photocatalyst deposited bimetal co-catalysts such as Pd/Pt, Pd/Au and Pt/Au were also investigated. The Pd/Pt-WO3 photocatalyst was found to show the highest photocatalytic activity for phenol formation due to an effective oxygen reduction reaction (ORR) for bimetallic Pd/Pt cocatalyst. From the experimental and theoretical studies, phenol was confirmed to form by the insertion of OH derived from H2O into benzene, and simultaneous cleavage of benzylic carbon-hydrogen bond (Csp2-H) by an assist of co-catalyst surface through the push-pull process.

Direct oxidation of benzene to phenol in a microreactor: Process parameters and reaction kinetics study

The direct synthesis of phenol from benzene and hydrogen peroxide was conducted in a microreactor. The effects of process parameters such as temperature, catalyst concentration, residence time, and molar ratio of hydrogen peroxide to benzene on the reaction performance were investigated systematically. The phenol yield could reach 15% while the selectivity was 94% with the set residence time of only 60 min at 55 ℃. Furthermore, a novel method was proposed to calculate the actual residence time for the reaction process with the in-situ produced gas due to the hydrogen peroxide decomposition. The actual residence time was found to be much shorter than the set residence time, especially at high temperatures. The reliability of this method at a certain temperature was verified with the kinetic study. The activation energies of phenol synthesis, hydrogen peroxide decomposition and p-benzoquinone formation were determined to be 99.52 KJ/mol, 99.43 KJ/mol and 63 KJ/mol, respectively.

Direct Synthesis of Phenols from Phenylboronic Acids in Aqueous Media Catalyzed by a Cu(0)‐Nanoparticles Biohybrid

AbstractSelective hydroxylation of different phenylboronic acids to phenols was successfully carried out by using Cu nanoparticles‐enzyme hybrid catalysts in water and room temperature. Different Cu‐enzyme hybrids containing Cu(II), Cu(I) and Cu(0) nanoparticles species respectively were tested on the monohydroxylation of phenylboronic acid under these mild conditions being hybrids containing Cu(0)NPs the best catalysts, with total selectivity and formation of phenol as unique product. Also, the addition of hydrogen peroxide or the increase of reaction temperature were tested but did not improved these results. The substrate scope was also demonstrated and the Cu(0)NPs hybrid showed excellent results in the monohydroxylation of different o‐, m‐, p‐substituted phenylboronic acid with final yields >95 %. This catalyst showed excellent recyclability after 5 cycles of use.

Direct Hydroxylation of Benzene to Phenol by Dielectric Barrier Discharge Plasma

Direct synthesis of phenol from benzene was realized using atmospheric dielectric barrier discharge (DBD) plasma. In the process, various experimental parameters such as irradiation time, electrode height, and discharge power were found to play crucial roles in determining the yield and selectivity of phenol. Also, serious carbonization phenomenon was observed at the surface of used electrode due to the extensive interaction between benzene and electrode, which greatly inhibited the hydroxylation of benzene to phenol. To resolve this issue, silica coated electrode was employed, and significant improvement of conversion efficiency was obtained. The yield of phenol as high as 19.5% could be obtained in the optimal condition, and its selectivity was 83.3% based on the analysis of gas chromatography-mass spectrometry.

NH3 -Driven Benzene C-H Activation with O2 that Opens a New Way for Selective Phenol Synthesis.

Catalytic benzene C-H activation toward selective phenol synthesis with O2 remains a stimulating challenge to be tackled. Phenol is currently produced industrially by the three-steps cumene process in liquid phase, which is energy-intensive and not environmentally friendly. Hence, there is a strong demand for an alternative gas-phase single-path reaction process. This account documents the pivotal confined single metal ion site platform with a sufficiently large coordination sphere in β zeolite pores, which promotes the unprecedented catalysis for the selective benzene hydroxylation with O2 under coexisting NH3 by the new inter-ligand concerted mechanism. Among alkali and alkaline-earth metal ions and transition and precious metal ions, single Cs+ and Rb+ sites with ion diameters >0.300 nm in the β pores exhibited good performances for the direct phenol synthesis in a gas-phase single-path reaction process. The single Cs+ and Rb+ sites that possess neither significant Lewis acidic-basic property nor redox property, cannot activate benzene, O2 , and NH3 , respectively, whereas when they coadsorbed together, the reaction of the inter-coadsorbates on the single alkali-metal ion site proceeds concertedly (the inter-ligand concerted mechanism), bringing about the benzene C-H activation toward phenol synthesis. The NH3 -driven benzene C-H activation with O2 was compared to the switchover of the reaction pathways from the deep oxidation to selective oxidation of benzene by coexisting NH3 on Pt6 metallic cluster/β and Ni4 O4 oxide cluster/β. The NH3 -driven selective oxidation mechanism observed with the Cs+ /β and Rb+ /β differs from the traditional redox catalysis (Mars-van Krevelen) mechanism, simple Langmuir-Hinshelwood mechanism, and acid-base catalysis mechanism involving clearly defined interaction modes. The present catalysis concept opens a new way for catalytic selective oxidation processes involving direct phenol synthesis.

Copper Immobilized on Isonicotinic Acid Hydrazide Functionalized Nano‐Magnetite as a Novel Recyclable Catalyst for Direct Synthesis of Phenols and Anilines

AbstractA new nano‐catalyst which contains a core of magnetic Fe3O4 nanoparticles (NPs) has been fabricated. It is covered via isonicotinic acid hydrazide and copper (Cu). In this sense, Isonicotinic acid hydrazide (INH) is applied because of its ability as a bidendental ligand and pharmaceutical activity in order to be used for the complexion and connection of Cu on Fe3O4 surface for the synthesis of Fe3O4@INH@Cu (INH= Isonicotinic acid hydrazide). In this regard, Fe3O4@INH@Cu as a heterogeneous nanocatalyst for the cross‐coupling of aryl halides with potassium hydroxide (KOH) as the hydroxide source and ammonium acetate (NH4OAc), as the amine source in the presence of cesium carbonate (Cs2CO3) in polyethylene glycol (PEG‐400), has been applied. The catalyst is a new magnetically recyclable catalytic system with easy preparation and purification, high activity, eco‐friendly and economic advantages.

Synthesis, structural configuration and DFT molecular orbital studies of [Mn-2[benzo[b]oxazole] acetonitrile] complexes encapsulated in ZSM-5: Direct synthesis of phenol by benzene hydroxylation

In situ synthesis of Mn-BOA [BOA = 2[benzo[b]oxazole] acetonitrile] complexes with loadings from 7.8 to 12.3 wt% in the microporous structure of zeolite ZSM-5 (Si/Al = 38) by the zeolite synthesis method was reported. The structure and characterization of the prepared samples have been identified by elemental analyses, XRD, XPS, EPR, FT-IR, UV-vis, TGA/DTGA, mass spectroscopy and pore structure analysis by nitrogen adsorption at −196 °C. A monotonic increase in crystallinity up to Mn-BOA(10.3%)/Z was shown and hence must be attributed to templating effect of manganese complex. Concurrently, the surface areas and pore volumes were decreased, suggesting that the complex remained intact within the zeolite walls. The XPS analysis of Mn-BOA(9.3%)/Z and Mn-BOA(12.3%)/Z confirm that manganese exists in the +2 oxidation state, though the latter only has a satellite feature around 646 eV which could be a result of the presence of Mn2O3. The EPR of neat complex in solution exhibited broad spectra corresponding to nearest neighbor spin-spin interactions, whereas Mn-BOA(9.1%)/Z showed well resolved metal hyperfine features as in case of the spectra in dilute frozen solutions. Theoretically bond lengths, bond angles, energies of the highest occupied (HOMO), lowest unoccupied (LUMO) molecular orbital levels, reactivity parameters and the molecular electrostatic potential (ESP) have been calculated for all samples. The catalytic activity of the synthesized samples towards benzene hydroxylation to phenol using H2O2 as a green oxidant at room temperature was evaluated. The effects of contact time, catalyst amount, and concentration of benzene and H2O2 on the conversion rate were investigated. The encapsulated complexes showed higher activities compared to that of the neat complex.

Direct synthesis of phenol by novel [FeFe]-hydrogenase model complexes as catalysts of benzene hydroxylation with H2O2

Compared the catalytic performance of complexes 1–3, the complex 2 has the highest phenol yield (24.6%) and phenol selectivity (92%), which has the highest electron densities of the catalytically active sites.

Selective Synthesis of Phenol from Benzene with O2 by Switchover of the Reaction Pathway from Complete Oxidation to Selective Hydroxylation by NH3 on Ir/β and Ni/β Catalysts

AbstractNew and selective IrO2 cluster/β and NiO cluster/β catalysts have been synthesized for the direct synthesis of phenol from benzene with O2 in gas‐phase single‐path flow reactions. Phenol is generated by switchover of the reaction pathway from complete oxidation of benzene to selective hydroxylation of benzene by NH3. The active oxide‐cluster structures in the β pores have been characterized by XAFS, XPS, STEM‐EDS, XRD, and DFT calculations. The reaction profile and the role of NH3 in the synthesis of phenol on the proposed Ni4O4 cluster have also been simulated by DFT calculations.

Structure of the Active Platinum Cluster and Reaction Pathway of the Selective Synthesis of Phenol from Benzene and Oxygen Regulated with Ammonia on a Platinum Cluster/β-Zeolite Catalyst Studied by DFT Calculations.

DFT calculations were used to investigate the structure of the active Pt cluster and the catalytic reaction pathway for the selective synthesis of phenol from benzene and molecular oxygen regulated with ammonia on a Pt cluster/β-zeolite catalyst that was reported to be active for the selective hydroxylation of benzene only in the coexistence of ammonia. It was found that Pt5-Pt6 clusters were active for the direct synthesis of phenol, and they provided the reaction sites for bond rearrangements among ammonia, oxygen, and benzene; furthermore, the coexistence of ammonia was crucial for the selective oxidation of benzene to phenol, as it suppressed benzene combustion to CO2 and promoted the selective synthesis of phenol. It was further found that water coexisting in the system also played a significant role in desorbing phenol on the Pt cluster surface, which resulted in promotion of the overall selective synthesis of phenol. The energy diagram for the reaction sequences and the structures of the transition states were obtained, which indicated the origin of the Pt/β catalysis.

Development of a high-performance nanostructured V2O5/SnO2 catalyst for efficient benzene hydroxylation

Nanostructured vanadium-tin oxide (V2O5/SnO2) catalysts with V2O5 loading in a range of 5–20wt% have been synthesized. The V2O5/SnO2 nanostructures exhibited effective catalytic performance in the hydroxylation of benzene to phenol using H2O2 as the terminal oxidant. The structure of the catalysts was studied using various techniques, such as XRD, Raman spectroscopy, SEM, EDX, TEM/HRTEM, STEM-HAADF, and H2-TPR and the adsorption/desorption of nitrogen. The Raman study supported the formation of certain monomeric and polymeric surface vanadium species and a crystalline V2O5 phase on their respective dehydrated mixed V2O5/SnO2 nanostructured catalysts depending on the vanadium loading. TEM studies revealed the morphology of V2O5 and SnO2 to be characterized by the formation of nanoparticles with a size of approximately 20nm. Moreover, the dispersion of V2O5 on SnO2 was also found to be influenced by V2O5 loading where a high loading of 20wt% exhibited an agglomeration of particles, which affected its catalytic activity. The V2O5/SnO2 catalysts resulted in modified redox properties, as evidenced by the H2-TPR results. These structural developments of mixed V2O5/SnO2 presented a highly active catalyst for the hydroxylation of benzene to phenol affording up to a 34% conversion, while preserving a phenol selectivity of 96% for a sample of V2O5/SnO2 containing 10wt% V2O5. The catalytic results indicated that the vanadium content in V2O5/SnO2 played an important role not only in improved substrate conversion but also in preserving a high selectivity for phenol. This was also evident from the correlation of the different vanadium phases for pure and composite catalysts with their respective catalytic results. Both polymeric and monomeric vanadium species on an SnO2 surface proved to be critical for the high catalytic performance of the catalyst. The high catalytic performance displayed by V2O5/SnO2 can provide opportunities for further development as a green and economical protocol for direct phenol synthesis from benzene hydroxylation with excellent catalyst recyclability.

Hydroxylation of benzene to phenol over magnetic recyclable nanostructured CuFe mixed-oxide catalyst

A highly active and magnetically recyclable nanostructured copper–iron oxide (CuFe) catalyst has been synthesized for hydroxylation of benzene to phenol under mild reaction conditions. The obtained catalytic results were correlated with the catalyst structure, which was characterized by XRD, SEM, TEM, EDX, H2-TPR and BET. The catalytic results indicated that the CuFe mixed oxide samples exhibited superior performance compared to its analogous single nano-oxide catalysts. The influence of the reaction condition variables, such as the solvent, reaction temperature, time, and amount of H2O2 oxidant, were investigated. Under optimized conditions, CuFe resulted in benzene conversion of 44% at a phenol selectivity of 91% and a corresponding combined hydroquinone/catechol/benzoquinone selectivity of 9%. In addition, the catalytic activity of the nano-oxide CuFe was significantly affected by the different calcination temperatures due to the induced catalyst structure, which was confirmed by the characterization results. This enhanced activity was due to the structural phases and redox modification resulting from the interface between the Cu and Fe metals, which was caused by varying calcination temperatures. The activity of CuFe does not require the formation of the typical favored CuFe2O4 spinel to achieve a highly active catalyst, which results from the enhanced redox potentials. CuFe is highly recyclable due to its magnetic nature, which results in an excellent ecofriendly catalyst for the direct synthesis of phenol from benzene hydroxylation.

Facile synthesis of POM@MOF embedded in SBA-15 as a steady catalyst for the hydroxylation of benzene

We present here a new hybrid material (POM@MOF@SBA-15, PMS) in which metal organic framework (MOF) MOF-199 encapsulated Kegginpolyoxometalate (POM) catalyst (names as POM@MOF) was facilely confined in mesoporous SBA-15. This mesoporous SBA-15 confined MOF-199 with encapsulated Keggin POM material was exploited to act as a stable heterogeneous POMs-based catalyst in a liquid oxidative reaction medium. Cycling experiments of the PMS catalyst were carried out in the direct synthesis of phenol from benzene and demonstrated unprecedented stability of this novel type PMS catalyst.

Ferrocene‐Modified Carbon Nitride for Direct Oxidation of Benzene to Phenol with Visible Light

Ferrocene moieties were heterogenized onto carbon nitride polymers by a covalent -C=N- linkage bridging the two conjugation systems, enabling the merging of the redox function of ferrocene with carbon nitride photocatalysis to construct a heterogeneous Photo-Fenton system for green organocatalysis at neutral conditions. The synergistic donor-acceptor interaction between the carbon nitride matrix and ferrocene group, improved exciton splitting, and coupled photocatalytic performance allowed the direct synthesis of phenol from benzene in the presence of H2 O2 under visible light irradiation. This innovative modification method will offer an avenue to construct functionalized two-dimensional polymers useful also for other green synthesis processes using solar irradiation.

Direct Synthesis of Phenol from Benzene and O2, Regulated by NH3 on Pt/β and Pt‐Re/ZSM‐5 Catalysts

Best director: The direct synthesis of phenol from benzene and O2 was performed with 78–94 % selectivity on Pt/β and Pt-Re/ZSM-5 catalysts, regulated by NH3 (see figure, (1)). An alternating process (see figure, (2)-1 and (2)-2) afforded the selective synthesis of phenol with 83–99.8 % selectivity, whilst minimizing the consumption of NH3. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Direct synthesis of phenol from benzene catalyzed by multi-V-POMs complex

A novel catalyst, [Mo2V2O9(bpy)6][PMo11VO40], was synthesized by the self-assembling of [PMo11VO40]4− and [Mo2V2O9(bpy)6]4+ unit and characterized by elemental analyses, TG, IR, X-ray powder diffraction and X-ray single crystal diffraction. [Mo2V2O9(bpy)6][PMo11VO40] with multi-isolated active sites showed good catalytic activities for hydroxylation of benzene to phenol. A high yield of phenol (25.5%) with selectivity to phenol of 90.7% was obtained using H2O2 as oxidant. The catalyst can be recycled for 5 times while its structure was unchanged and its catalytic activity was maintained.

Exceptional activity for direct synthesis of phenol from benzene over PMoV@MOF with O2

Abstract Three novel catalysts named as PMo12 − nVn@HKUST-1 (n = 1–3) were designed and obtained through encapsulating vanadium-doped Keggin polyoxometalates (POMs) PMo12 − n Vn into the framework HKUST-1 (also denoted as Cu3(BTC)2, MOF-199). The character structure of PMo12 − n Vn@HKUST-1 was elucidated through the single crystal XRD of PMo11V@HKUST-1. Reaction rate could be greatly enhanced by PMo12 − n Vn@HKUST-1 in liquid hydroxylation of benzene with O2. Only in 20 min, a high TOF (44.2 h− 1) of PMo9V3@HKUST-1 was obtained.

Highly Selective Synthesis of Phenol from Benzene over a Vanadium‐Doped Graphitic Carbon Nitride Catalyst

AbstractDesign and preparation of efficient and economical catalysts for direct hydroxylation of benzene to phenol is an important topic. In this work, a series of metal‐doped graphitic carbon nitride catalyst (Cu‐, Fe‐, V‐, Co‐, and Ni‐g‐C3N4) were successfully synthesized by using urea as the precursor through a facile and efficient method. The catalysts were characterized systematically using N2 adsorption–desorption, FTIR, thermogravimetric analysis, powder X‐ray diffraction, and X‐ray photoelectron spectroscopy techniques. It was found that the vanadium‐doped graphitic carbon nitride catalyst V‐g‐C3N4 was the most efficient catalyst for the direct synthesis of phenol from benzene with hydrogen peroxide as the oxidant and it could be recycled at least 4 times. The influence of reaction conditions such as the solvent, reaction temperature, reaction time, and the amounts of catalyst and hydrogen peroxide were investigated. Under optimized conditions, 18.2 % yield of phenol was obtained with the selectivity to phenol as high as 100 %.

Direct Synthesis of Phenol from Benzene over Platinum-loaded Tungsten(VI) Oxide Photocatalysts with Water and Molecular Oxygen

Abstract Tungsten(VI) oxide loaded with nanoparticulate platinum (Pt/WO3) was demonstrated for the first time to exhibit photocatalytic activity for direct synthesis of phenol from benzene using water and molecular oxygen as reactants under ultraviolet or visible light irradiation; the selectivity for phenol (e.g., 74% at 69% of benzene conversion) on Pt/WO3 photocatalysts was much higher than those on platinum-loaded titanium(IV) oxide (Pt/TiO2) photocatalysts.

Direct Synthesis of Phenol from Benzene on an Activated Carbon Catalyst Treated with Nitric Acid

Commercially available coal-based activated carbon was treated by nitric acid with different concentrations and the resultant samples were used as catalysts for the direct hydroxylation of benzene to phenol in acetonitrile. Boehm titration, X-ray photoelectron spectroscopy, scanning electron microscope coupled with an energy dispersive X-ray microanalyzer, and Brunauer-Emmett-Teller method were used to characterize the samples. The number of carboxyl groups on the surface was found to be the main factor affecting the catalytic activity. An optimum catalytic performance with a yield of 15.7% and a selectivity of 87.2% to phenol was obtained.