Benzene Hydroxylation Reaction Research Articles

DFT Mechanistic Investigation into Ni(II)-Catalyzed Hydroxylation of Benzene to Phenol by H2O2.

Introduction of oxygen into aromatic C-H bonds is intriguing from both fundamental and practical perspectives. Although the 3d metal-catalyzed hydroxylation of arenes by H2O2 has been developed by several prominent researchers, a definitive mechanism for these crucial transformations remains elusive. Herein, density functional theory calculations were used to shed light on the mechanism of the established hydroxylation reaction of benzene with H2O2, catalyzed by [NiII(tepa)]2+ (tepa = tris[2-(pyridin-2-yl)ethyl]amine). Dinickel(III) bis(μ-oxo) species have been proposed as the key intermediate responsible for the benzene hydroxylation reaction. Our findings indicate that while the dinickel dioxygen species can be generated as a stable structure, it cannot serve as an active catalyst in this transformation. The calculations allowed us to unveil an unprecedented mechanism composed of six main steps as follows: (i) deprotonation of coordinated H2O2, (ii) oxidative addition, (iii) water elimination, (iv) benzene addition, (v) ketone generation, and (vi) tautomerization and regeneration of the active catalyst. Addition of benzene to oxygen, which occurs via a radical mechanism, turns out to be the rate-determining step in the overall reaction. This study demonstrates the critical role of Ni-oxyl species in such transformations, highlighting how the unpaired spin density value on oxygen and positive charges on the Ni-O• complex affect the activation barrier for benzene addition.

An iron-containing POM-based hybrid compound as a heterogeneous catalyst for one-step hydroxylation of benzene to phenol.

It is a major challenge to perform one-pot hydroxylation of benzene to phenol under mild conditions, which replaces the environmentally harmful cumene method. Thus, finding highly efficient heterogeneous catalysts that can be recycled is extremely significant. Herein, a (POM)-based hybrid compound {[FeII(pyim)2(C2H5O)][FeII(pyim)2(H2O)][PMoV2MoVI9VIV3O42]}·H2O (pyim = 2-(2-pyridyl)benzimidazole) (Fe2-PMo11V3) was successfully prepared by hydrothermal synthesis using typical Keggin POMs, iron ions and pyim ligands. Single-crystal diffraction shows that the Fe-pyim unit in Fe2-PMo11V3 forms a stable double-supported skeleton by Fe-O bonding to the polyacid anion. Remarkably, due to the introduction of vanadium, Fe2-PMo11V3 forms a divanadium-capped conformation. Benzene oxidation experiments indicated that Fe2-PMo11V3 can catalyze the benzene hydroxylation reaction to phenol in a mixed solution of acetonitrile and acetic acid containing H2O2 at 60 °C, affording a phenol yield of about 16.2% and a selectivity of about 94%.

Understanding the Density-Dependent Activity of Cu Single-Atom Catalyst in the Benzene Hydroxylation Reaction

Regulating the density of metal single atoms and exploring the interaction among them are showing great potential to further raise the performance of single-atom catalysts (SACs). Herein, we produce a series of Cu SACs with densities ranging from 0.1 to 2.4 atoms/nm2 and find that the catalytic activity is proportional to Cu single-atom density in the benzene hydroxylation reaction. Mechanistic studies reveal that the interactions among neighboring single-atom moieties in ultra-high-density Cu SAC alter the electronic structures of Cu single atoms, resulting in stronger •OH adsorption, which is beneficial for the benzene hydroxylation reaction by suppressing the O2 formation side reaction. The adsorption energy of hydroxyl radicals is further proposed and verified as a key descriptor to explain the reaction differences of Cu SACs with various densities. As a result, the ultra-high-density Cu SAC of 2.4 atoms/nm2 (21.3 wt %) exhibits maximum mass specific activity and H2O2 utilization efficiency, which are both significantly higher than the reported results in the literature and solved the key challenges of SACs in the benzene hydroxylation reaction. This study sheds light on how the SAC density affects active sites and offers a practical catalyst for phenol production by the H2O2 route.

Catalytic Mechanisms and Active Species of Benzene Hydroxylation Reaction System Based on Fe-Based Enzyme-Mimetic Structure

Catalytic Mechanisms and Active Species of Benzene Hydroxylation Reaction System Based on Fe-Based Enzyme-Mimetic Structure

Combined computational and experimental investigation on the Fenton reagent catalysed hydroxylation of benzene

BackgroundPhenol is one of the most important chemicals in industry, generally produced from benzene in cumene processes. Alternatively, the direct hydroxylation of benzene catalysed by Fenton reagent has been a potentially sustainable process for the production of phenol. MethodsComputational calculation method combined with experiments were both employed to investigate the Fenton reagent catalysed hydroxylation of benzene. Significant findingsComputational calculation turned out that the H migration National Institutes of Health (NIH) shift in the benzene hydroxylation reaction including intramolecular immigration and an intermolecular process. The activation energy (ΔG) for the H migration between IM2 molecules was 17.5 kcal mol−1, while the ΔG for the intramolecular H transfer was 49.4 kcal mol−1. The crucial intermediates in the direct hydroxylation reaction were characterised by a variety of analysis methods. There were three types of C-C bonds in IM1 with Mayer bond order (MBO) equivalent to 1.272, 1.581, and 1.041 respectively, and the C-C bonds in IM2 were not equal based on the localised orbitals and orbital composition analysis and a series of electronic structure information. Moreover, the global electron delocalisation analysis visually demonstrated an uneven distribution of π electron, revealing the aromaticity of these two intermediates. These two intermediates exhibited both aromaticity and antiaromaticity features under external magnetic conditions. Notably, the nuclear magnetic resonance results showed the existence of one of the prominent intermediates.

Improved Durability and Activity of FeVO4 toward Photocatalytic Benzene Hydroxylation by Atomic Layer Deposited Al2O3

AbstractSelective hydroxylation of benzene to phenol over a visible light driven photocatalyst is a sustainable approach for the green synthesis of phenol. Iron vanadate (FeVO4) nanorods with an intrinsic photo‐Fenton catalytic behavior toward H2O2 activation is a promising candidate photocatalyst for the benzene hydroxylation reaction; however, its photocatalytic performance was greatly limited by the serious leaching of metals during the hydroxylation process. Herein, it has been demonstrated that this issue can be well addressed by the conformably coating of FeVO4 nanorods with an atomically‐precise thickness controlled dense Al2O3 layer (FeVO4@Al2O3) through the atomic layer deposition (ALD) technology. The Al2O3 nanolayer can well protect the FeVO4 nanorods from directly contacting with the reaction solution, thus effectively suppressing the leaching of metals during the photocatalytic hydroxylation process. In addition, the Al2O3 coating on FeVO4 also facilitates the kinetic control of heterogeneous benzene hydroxylation reaction over the catalyst surface, such as the benzene adsorption behavior and the photo‐Fenton activation of H2O2. As a result, FeVO4@Al2O3 exhibited an enhanced photocatalytic performance with a good durability in the long‐term production of phenol.

Carbon encapsulated bimetallic FeCo nanoalloys for one-step hydroxylation of benzene to phenol

Carbon encapsulated iron catalysts hold great potential for one-step hydroxylation of benzene to phenol due to their unique core-shell nanostructures. However, their catalytic performance is moderate, since the carbon shells have impeded their activity toward H2O2 activation. Herein, we demonstrate that alloying engineering of Fe cores with Co atoms is a promising strategy to address the issue about H2O2 activation. The incorporation of Co into Fe cores can generate strong synergetic effects to promote H2O2 activation, while still maintaining the structural benefits of carbon shells for benzene hydroxylation reaction. As a result, the phenol yield obtained on carbon encapsulated FeCo (FeCo@C) reaches to 26.4 ± 0.7% with a selectivity of 96.2 ± 1.2%, much higher than that of Fe@C and Co@C. With the improved intrinsic catalytic behavior toward H2O2 activation and well-reserved carbon structure benefits, FeCo@C should be a promising catalyst for a broad liquid-phase reactions using H2O2 as the oxidant.

Theoretical Investigation into Selective Benzene Hydroxylation by Ruthenium-Substituted Keggin-Type Polyoxometalates.

Benzene hydroxylation catalyzed by ruthenium-substituted Keggin-type polyoxometalates [RuV(O)XW11O39]n- (RuVOX; X = Al, Ga, Si, Ge, P, As, S; heteroatoms; 3 ≤ n ≤ 6) is investigated using the density functional theory approach. As a possible side reaction, the water oxidation reaction is also considered. We found that the rate-determining step for water oxidation by RuVOX requires a higher activation free energy than the benzene hydroxylation reaction, suggesting that all of the RuVOX catalysts show high chemoselectivity toward benzene hydroxylation. Additionally, the heteroatom effect in benzene hydroxylation by RuVOX is discussed. The replacement of Si by X induces changes in the bond length of μ4O-X, resulting in a change in the activation free energy for benzene hydroxylation by RuVOX. Consequentially, RuVOS is expected to be the most effective catalyst among the (RuVOX) catalysts for the benzene hydroxylation reaction.

Unique functionalities of carbon shells coating on ZnFe2O4 for enhanced photocatalytic hydroxylation of benzene to phenol

Hydroxylation of benzene to phenol over a photocatalyst is a green approach toward phenol production. ZnFe2O4 (ZFO) with an intrinsic peroxidase-like catalytic behavior toward H2O2 activation is an emerging photocatalyst for benzene hydroxylation reaction; however, its catalytic performance is greatly limited by the fast charge recombination, inevitable metal leaching and hydrophilic surface structure. Herein, the encapsulation of ZFO by carbons (ZFO@C) is an effective solution to address these issues. The carbons conformably coating on ZFO not only protect them from corrosion and metal leaching, but also enable the generation of a strong electronic contact between them to facilitate charge separation. In addition, the carbons also increase the surface affinity for benzene adsorption. As a result, ZFO@C exhibited a significant enhanced photocatalytic activity and durability for phenol synthesis. Furthermore, ZFO@C with carbon derived unique functionalities will have a broad application in photocatalytic green synthesis of fine chemicals.

Polyoxometalate-Based Metal-Organic Frameworks with Unique High-Nuclearity Water Clusters.

The maximum exposure of polyoxometalates (POMs) is of great significance to enhance the catalytic performance of HKUST-1 with incorporated Keggin-type POMs. Herein, two phosphovanadomolybdates were encapsulated into the HKUST-1 via a hydrothermal method to obtain two polyoxometalate-based metal-organic frameworks, formulated as [Cu12(BTC)8(H2O)12][H4PMo11VO40]@(H2O)30 (1) and [Cu12(BTC)8(H2O)12][H5PMo10V2O40]@(H2O)49 (2). Single-crystal X-ray diffraction analysis indicates that two compounds contain unique high-nuclearity water clusters without organic counter cations. The octahedral-shaped water cluster (H2O)30 was constructed from square-pyramid-shaped (H2O)5 for compound 1, while the huge cage-shaped water cluster (H2O)49 of compound 2 consisted of crown-like (H2O)8 and one water molecule, which substitute the organic counter cations involved in the structural construction. More importantly, after removing the water clusters via simple heat treatment, the active sites of the two compounds were fully exposed, leading to good catalytic activities for both benzene hydroxylation reaction and oxidative desulfurization. Furthermore, the catalytic test confirmed that compound 2 may be a bifunctional heterogeneous catalyst with great promise for both benzene hydroxylation and oxidative desulfurization.

Cerium promoted V-g-C3N4 as highly efficient heterogeneous catalysts for the direct benzene hydroxylation.

A series of Cex-V-g-C3N4 catalysts with different cerium content were synthesized by a facile co-assembly method. Compared with pure V-g-C3N4 catalyst, the addition of cerium facilitated the high dispersion of vanadium species as well as the benzene adsorption ability of the corresponding catalysts. Also, the existence of cerium promoted the partial reduction of vanadium species, which improved the redox property of vanadium species as the active centres. The Cex-V-g-C3N4 catalysts showed considerably improved activity in the benzene hydroxylation reaction compared with V-g-C3N4 catalyst. Among the catalysts studied, Ce0.07-0.07 V-g-C3N4 exhibited the best catalytic activity with a benzene conversion of 33.7% and a phenol yield of 32.3% with good structural and catalytic stability, while only 24.7% of benzene conversion and phenol yield of 24.2% were obtained over 0.07 V-g-C3N4.

Vanadium-containing mesoporous carbon and mesoporous carbon nanoparticles as catalysts for benzene hydroxylation reaction

Highly ordered mesoporous carbon of body-centered cubic structure was synthesized by the evaporation induced self-assembly method using Pluronic F127 and phenolic resol as the template and carbon source, respectively. Vanadium species were introduced to the carbon support by both co-assembly and impregnation strategies for comparison. Ordered mesoporous carbon nanoparticles of the same body-centered cubic structure were also synthesized via a facile soft-template method, followed by the incorporation of vanadium species via impregnation. The obtained three different series of vanadium-containing carbon catalysts were tested in the direct benzene hydroxylation reaction using H2O2 as an oxidant. The vanadium supporting mesoporous carbon nanoparticles, due to the open framework and short channels for fast reactants diffusion and the easily accessible active vanadium species for reactants activation, exhibited superior catalytic activity to other series of catalysts. Particularly, the 4V/MCN-S catalyst showed the best catalytic performance among the studied catalysts with a benzene conversion of 38.2% and phenol selectivity of 96.1%, along with good stability during five recycles.

Vanadium supported on graphitic carbon nitride as a heterogeneous catalyst for the direct oxidation of benzene to phenol

A series of graphitic carbon nitride supported vanadium catalysts (xV/g-C3N4) with different vanadium contents (x/%) were prepared by impregnation. XRD, FT-IR, TEM, TG-DTG, nitrogen adsorption and XPS characterizations were conducted which revealed a strong interaction between the vanadium species and g-C3N4 support. 8V/g-C3N4 exhibited the highest activity and showed stable recyclability in the benzene hydroxylation reaction with a benzene conversion of 24.6% and phenol selectivity of 99.2% under the optimized conditions. The excellent catalytic performance of xV/g-C3N4 was due to the integration of vanadium species with high catalytic activity and the g-C3N4 support in their interaction with the benzene substrate

CuO Impregnated mesoporous silica KIT-6: a simple and efficient catalyst for benzene hydroxylation by C–H activation and styrene epoxidation reactions

Copper oxide doped mesoporous KIT-6 materials were synthesized by ultrasonication as impregnation method. The highly ordered nature of mesoporous CuO-KIT-6 materials analyzed by low angle X-ray diffraction. The high surface area, pore diameter and mesoporous nature of synthesized materials were confirmed by BET surface area analysis. Si–O–Si, Si–OH and Cu–O–Si bonds in the framework of CuO-KIT-6 were verified by FTIR spectroscopy. The Cu2+ ← O2− charge-transfer transitions and d–d transitions of dispersed Cu2+ on ordered mesoporous KIT-6 were identified by DRS UV–Vis spectroscopy. The morphology of the synthesized CuO-KIT-6 materials was analyzed by HR-SEM. The 3D ordered nature of CuO-KIT-6 confirmed by TEM analysis. The highly ordered 3D mesoporous CuO-KIT-6 materials are excellent catalyst for benzene hydroxylation reaction through C-H activation and styrene epoxidation reaction with 30 % aqueous H2O2. The catalyst CuO-KIT-6 itself showed a good conversion towards both reactions.

The Effect of Vanadium Oxide on The Catalytic Activity of Titanium Silicalite in Conversion of Benzene to Phenol

Phenol is one of the most important intermediate for petrochemical, agrochemical, and plastics industries<em>. </em>Almost<em> 95% phenol is </em>produced using cumene method. Cumene method is a multi-stage process with many disadvantages including the difficulties to gain phenol product in maximum quantities and production of co-product such as acetone which has great amount in market nowadays. One of the alternative routes to produce phenol which has more advantages is through benzene hydroxylation reaction using H<sub>2</sub>O<sub>2</sub> as oxidant agent and Titanium Silikalit-1 (TS-1) as catalyst. TS-1 catalyst has high catalytic activity and selectivity in selective oxidation reaction of aromatic compounds with H2O2 which important for commercial industries. However, the reaction rate is tend to be low because TS-1 has hydrophobic nature and as the result H2O2 adsorption which has hydrophilic nature towards active sites of TS-1 is also become slower. Addition of metal oxide V2O5 could enhance hydrophilicity of TS-1 catalyst. Liquid phase catalytic benzene hydroxylation using hydrogen peroxide as oxidant was carried out over vanadium (V) oxide-modified TS-1 catalyst (V<sub>2</sub>O<sub>5</sub>/TS-1), that were prepared by impregnation method using vanadium methavanadate as precursor and characterized by pyridine adsorption and hydrophilicity techniques.

Direct hydroxylation of benzene to phenol using H2O2 as an oxidant over vanadium-containing mesoporous carbon catalysts

A series of vanadium-containing mesoporous carbon catalysts were synthesized by the co-assembly method using phenolic resol, vanadyl acetylacetonate [VO(acac)2], and Pluronic F127 as carbon source, metal source, and template, respectively. The effects of the calcination temperature on the transformation of vanadium species and the carbon framework were investigated. During the calcination treatment, the nanoparticles of vanadium species mainly confined in the carbon matrix were formed along with the further cross-linking and carbonization of the phenolic resol network. The obtained catalysts exhibited the two-dimensional hexagonal mesostructures, high surface areas, and uniform pore sizes. Their catalytic activity in the benzene hydroxylation reaction was tested and the 0.2-V-C-600 catalyst showed the high performance with the benzene conversion of 31.8% and phenol selectivity of 94.9% as well as the good stability in recycles.

Direct hydroxylation of benzene to phenol on Cu–V bimetal modified HMS catalysts

A series of mesoporous Cux–V-HMS catalysts with different copper content were prepared by the co-synthesis method. The addition of copper improves the benzene adsorption ability of the catalyst and the redox property of vanadium species, which facilitate the benzene hydroxylation reaction. Among the catalysts studied, Cu0.90–V-HMS exhibited the best catalytic activity with a phenol yield of 29.0% compared with 20.7% over V-HMS catalyst.

Catalytic Activity and Structure Properties of Doped VOHPO<SUB>4</SUB>·0.5H<SUB>2</SUB>O with Nanosized Ru, Au, Fe and Mn in Benzene Hydroxylation

The promotional effect of nanosized Ru, Fe, Au, and Mn particles on VOHPO4 x 0.5H2O (VHP) catalytic properties was investigated in benzene hydroxylation reaction using hydrogen hydroperoxide (H2O2) as oxidant. Catalytic results indicated a profound effect of the nanoparticle dopants on VHP catalyst activity and products distribution. Amongst the promoted VHP catalysts, Au/VHP exhibited high catalytic effect with benzene conversion of 76% at a combined 85.5% selectivity toward the formation of phenol and hydroquinone achieved in 6 h under optimised reaction conditions. The extended scope application of nanosized doped Au-VHP showed to provide an effective catalyst for activation of the aromatic hydrocarbons C-H bonds into oxygenate derivatives. The catalyst could be re-used for several cycles with insignificant loss of activity. The doped nanosized Au-VHP catalyst provide a clean promising catalytic route based on heterogeneous catalysis for transformation of aromatics into value-added oxygenates.

PREPARATION, CHARACTERIZATION AND CATALYTIC ACTIVITY OF CuO/TS-1 ON BENZENE HYDROXYLATION REACTION

CuO/TS-1 catalysts have been prepared and tested in the benzene hydroxylation. TS-1 was synthesized by hydrothermal method, while CuO/TS-1 was prepared by impregnation method using Cu(NO)2.3H2O as precursor. Catalysts were characterized by using X-ray diffraction (XRD), infrared spectroscopy (IR), and N2 adsorption-desorption techniques. The catalytic activity was tested in the hydroxylation reaction of benzene. The products were analyzed using gas chromatography. Catalyst characterization by XRD and IR techniques have showed that the catalyst structure was a MFI type of zeolite. XRD pattern have showed the orthorombic structure and indicated the presence of CuO aggregation. The results of the pyridine adsorption have found that the acidity of TS-1 and CuO/TS-1 were a Lewis acid and it’s increased with an increasing amount of CuO loading. The results of nitrogen adsorption analysis have showed decreasing of surface areas of catalyst with increasing amount of CuO loading. The optimum conditions of benzene hydroxylation was observed by 1%CuO/TS-1 catalyst at 70 °C, reaction time 2 h and acetic acid as the solvent yielded 27.6% of phenol with phenol selectivity was 75.5%.

Nature of vanadium species on vanadium silicalite-1 zeolite and their stability in hydroxylation reaction of benzene to phenol

The vanadium silicalite-1 (VS-1) zeolite catalysts with different vanadium contents were prepared by a modified hydrothermal synthesis method, and the one with the highest vanadium content (1.9 wt%) was treated by ammonium acetate (NH4OAc), H2O2 and/or acetic acid (HOAc). The samples were characterized by ICP, XRD, XPS, TPR, and DR UV-Vis to reveal the effect of the state of the vanadium species on the catalysts and to examine their leaching behavior under different conditions. The presence of H2O2 removed the vanadium oligomer loaded on the extra-framework of the VS-1. Highly dispersed distorted octahedral VV species located in the pore of zeolite were unstable in HOAc. The mononuclear octahedral VV, tetrahedral VV and VIV species in the framework showed good stability under the hydroxylation conditions. The VS-1 catalyst with 1.0 wt% of vanadium incorporation in the framework showed a stable hydroxylation activity yielding about 11% phenol (TOF = 63.0) with above 90% selectivity.