Hydroxylation Of Benzene Research Articles

Organic Ionic Liquid Grafted Nano‐CeO2: A Highly Efficient Photocatalyst for Hydroxylation of Benzene and Reduction of Cr (VI)

AbstractAn ionic liquid, namely imidazolium sulfonic acid chloride (ISAC) has been electrostatically grafted over cerium oxide nanoparticles to produce a nanocomposite, nano‐CeO2‐IL. The as‐prepared composite was characterized by various analytical techniques such as XRD, FT‐IR, SEM, TEM, XPS, BET, UV‐DRS, PL, and TGA to confirm the grafting of ISAC over CeO2 NPs. The photocatalytic process is regarded as the method of choice for the elimination of air pollutants because of its great efficiency and relatively benign working conditions. According to UV‐DRS spectra, its optical gap is 2.07 eV, which is appropriate for the visible light spectrum. The composite was investigated as a visible‐light‐driven photocatalyst for hydroxylation of benzene to phenol and heavy metal Cr (VI) reduction. Moreover, the scavenger experiments confirmed the detection of ⋅OH radicals which played a crucial role in the photocatalytic experiments. Within 60 minutes, 98.5 % of benzene was converted to phenol with 82.7 % selectivity in addition to 93.63 % Cr (VI) reduction within 30 mins. The photocatalytic reduction of Cr(VI) to Cr(III) follows a first‐order model with a rate constant of 0.027 min−1. The remarkably high photocatalytic performance of the catalyst may be ascribed to the synergistic interaction between the nano‐CeO2 catalyst and ionic liquid.

Mechanism of Benzene Hydroxylation on Tri-Iron Oxo-Centered Cluster-Based Metal–Organic Frameworks

Mechanism of Benzene Hydroxylation on Tri-Iron Oxo-Centered Cluster-Based Metal–Organic Frameworks

Boosting H2O2 utilization efficiency in benzene hydroxylation to phenol via isolated single VO4 site on hydrophobic poly(ionic liquid)-derivative

Hydrogen peroxide (H2O2)-mediated benzene hydroxylation is one of the most attractive avenues towards green synthesis of phenol, a crucial industrial feedstock. Nonetheless, it remains one challenge to explore efficient catalysts, especially the one allowing high H2O2 utilization efficiency to fulfill the safety production. In this work, isolated single VO4 sites were constructed on the hydrophobic poly(ionic liquid)-derivative through copolymerization of dinuclear imidazolyl ionic liquid and polyhedral oligomeric silsesquioxane (POSS), ion change with ammonium metavanadate (NH4VO3), and the pyrolysis under moderate temperature. The combination of V(IV) single sites and a hydrophobic surface made the catalyst effectively catalyzing the phenol synthesis from benzene oxidation with H2O2, giving phenol selectivity above 99 %, H2O2 utilization efficiency of 92 %, and turnover frequency (TOF) beyond 900 h−1. The catalyst was stably recycled and exhibited broad substrate compatibility. The pyrolysis step strengthened both stability and activity, significantly contributing to the high catalytic efficiency.

Enhanced photocatalytic performance of Cr doped MgO/Bi2O3 nanocomposite for efficient hydroxylation of benzene to phenol under visible-light irradiation

A series of Cr-doped MgO/Bi2O3 (Cr-MgO/Bi2O3) nanocomposites were prepared for the photocatalytic benzene hydroxylation to produce phenol by the visible-light exposure, and the catalyst dosage, solvents and volume ratio of benzene to H2O2 were thoroughly examined. The well-characterized photocatalyst (10% Cr- MgO/Bi2O3) by various physico-chemical and spectroscopic techniques was found to be highly efficient with an optimal phenol selectivity of 98.5% and yield of 13.8%, which were much higher than those obtained from bare Bi2O3, MgO and MgO/Bi2O3. The remarkably improved photocatalytic activity was resulted from the conduction of heterojunction between Bi2O3 and MgO, as well as the generation of a new trapping level within Cr-MgO/Bi2O3 by Cr doping, which greatly accelerated the photogenerated charge carriers separation. This work combining heterojunction conduction and transition metal doping exhibits promising potential for future applications in organic transformation reactions.

Fragmentation engineering on the edge of hydroxy-functional COFs for the enhanced photocatalytic production of H2O2 and direct photo-oxidation of benzene to phenol in aqueous systems

Structural design is important and challenging for the fabrication of covalent organic frameworks (COFs) in the photocatalytic applications. Hydroxyl groups have been found to be the active sites for O2 adsorption and promote the electron-donating conjugation effects, which favorable for the oxygen reduction reaction (ORR) in photocatalytic hydrogen peroxide (H2O2) evolution. This study reports the preparation of “fragmentized” COFs (TxHy-COFs) photocatalysts and their application in H2O2 synthesis, as well as the direct hydroxylation of benzene to phenol. The results demonstrate that the functional design of surface hydroxyl (–OH) modification on fragmentized TxHy-COFs was achieved by varying the feed ratio of TAPT and THTA monomers, which greatly enhances surface hydrophilicity and effectively improves the separation and transfer of photoexcited electrons and holes. Under visible light irradiation without sacrificial agents, the fragmentized T1H1.8-COF exhibits a boosting H2O2 yield of 2567 μmol g−1h−1, which is 4.2 times higher than the original T1H1-COF. Furthermore, the introduction of metal ions (Fe3+ etc.) into the COF framework through the impregnation method enables the in situ activation of H2O2, allowing the direct hydroxylation of benzene to phenol in aqueous systems, with yield of 9.4 % and selectivity of 99 %. The results of this work demonstrate that the prepared photocatalyst exhibits high stability and photocatalytic activity by structural design optimization, showing great potential for industrial applications in H2O2 production and direct photo-oxidation.

Facile synthesis of CuO/Cu-MOF/GO for efficient photocatalytic benzene hydroxylation to phenol

Facile synthesis of CuO/Cu-MOF/GO for efficient photocatalytic benzene hydroxylation to phenol

Engineering oxygen vacancies of 2D WO3 for visible-light-driven benzene hydroxylation with dioxygen

Solar-driven benzene oxidation with dioxygen (O2) provides a green and sustainable alternative for phenol production, but the construction of heterogeneous photocatalysts remains a huge challenge for efficient conversion under visible light irradiation and ambient conditions. Herein, we reported a facile microwave assisted strategy for the defect engineering of two-dimensional (2D) tungsten oxide while well maintaining the original crystalline architecture. Abundant oxygen vacancies were constructed on the 2D tungsten oxide, which remarkably promoted photochemical (light harvesting, charge separation and transfer) and O2 activation behaviors, this promotion effect was further strengthened by the hybridization with Pt species with the formation of Schottky junction. The champion catalyst enabled a high phenol yield of 11.3% with a selectivity of 91% in the visible-light-driven benzene hydroxylation with atmospheric O2 at room temperature. The catalyst can be facilely recovered and reused with stable activity. The oxygen vacancies and Pt co-catalyst were demonstrated to play vital roles in the photocatalytic formation of the reactive oxygen species (hydroxyl radials, ·OH) for effective oxidation.

A novel Cr-doped CdS/ZnO nanocomposite for efficient photocatalytic hydroxylation of benzene to phenol

In this study, Cr-doped CdS/ZnO (Cr-CdS/ZnO) nanocomposites were synthesized for the first time and systematically characterized using different physicochemical methods, such as XRD, SEM, HRTEM, UV-Vis DRS, XPS, PL, EIS and EPR, etc. The photocatalytic activity of the Cr-CdS/ZnO nanocomposites was evaluated for the hydroxylation of benzene to phenol using H2O2 as the oxidant under visible-light irradiation. The impacts of various reaction conditions, including the role of catalyst dosage, solvents and volume ratio of benzene to H2O2 were specifically investigated. Owing to the similar lattice structure and well-matched band positions of CdS and ZnO, generation of electrons and holes by CdS-captured photons, as well as separation and imigration of electrons to ZnO were all realized. Furthermore, Cr-doping favored the formation of a new trapping level in the band gap of the Cr-CdS/ZnO composite, which would not only enhance visible-light absorption capacity, but also inhibit the rapid recombination of photo-generated electron-hole pairs. As a result, an excellent phenol selectivity of 98% with a phenol yield of 11.1% was achieved, which was higher than those of the pristine Cr-CdS, Cr-ZnO and CdS/ZnO. In the end, a rational mechanism for enhanced photocatalytic activity of the synthesized composites under visible-light irradiation was also proposed. The visible-light absorption and remarkably improved photocatalytic performance for benzene hydroxylation enable the potential of Cr-CdS/ZnO nanocomposites for the application of photocatalytic green synthesis of fine chemicals.

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.

G-C3N4-modified Zr-Fc MOFs as a novel photocatalysis-self-Fenton system toward the direct hydroxylation of benzene to phenol.

In order to explore a green, economic, and sustainable phenol production process, a heterojunction semiconductor materials g-C3N4/Zr-Fc MOF was synthesized via an in situ synthesis method. With the synergistic effect of photocatalysis and the Fenton effect, the composite could effectively catalyze the direct hydroxylation of benzene to phenol under visible light irradiation. The yield of phenol and the selectivity were 13.84% and 99.38% under the optimal conditions, respectively, and it could still maintain high photocatalytic activity after 5 photocatalytic cycles. Therefore, the designed photocatalysis-self-Fenton system has great potential in the field of the direct hydroxylation of benzene to phenol.

An efficient photocatalysis-self-Fenton system based on Fe(ii)-MOF/g-C3N4for direct hydroxylation of benzene to phenol

With the synergistic effect of photocatalysis and the Fenton effect, the Fe(ii)-MOF/g-C3N4 could achieve efficient direct hydroxylation of benzene to phenol.

Tuning the selectivity of visible light-driven hydroxylation of benzene to phenol by using Cu, Fe and V oxides supported on N-doped TiO2

The Cu/N-TiO2 photocatalyst produces phenol faster than the other formulated photocatalysts. No reduction in benzene conversion (ca. 80%) and phenol yield (ca. 25%) was observed after 4 reuses, confirming the high stability of the catalytic system.

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

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.

Persulfate activation with sodium alginate/sulfide coated iron nanoparticles for degradation of tetrabromobisphenol a in soil

The accumulation of tetrabromobisphenol A (TBBPA) in soil posed a serious threat to ecosystem and human health. Sodium alginate/sulfide coated iron nanoparticles (SA@S–Fe NPs) was synthesized by a two-step modification of Fe NPs prepared with tung tree leaves extracting solution, and utilized as a persulfate (PS) activator to degrade TBBPA in soil. Response surface methodology (RSM) optimization showed a theoretical maximum TBBPA degradation reaching 99.79% at the 34.28 °C, SA@S–Fe NPs and PS additions of 3.57 g kg−1 and 36.35 mM, respectively. The degradation mechanism of TBBPA suggested that the main reactive species produced in the SA@S–Fe NPs/PS system were •OH, SO4•−, and O2•−. Proposed mechanisms for the degradation of TBBPA in soil involved debromination, benzene rings split, hydroxylation, demethylation, and complete mineralization to CO2 and H2O. We also further studied the effect to soil physicochemical properties and morphology structure during TBBPA degradation in SA@S–Fe NPs/PS system, which showed that SOM, TN, C/N and TOC slightly reduced, the heavy metals Fe, Cu and Zn still existed in stable residue form, and the soil morphology showed a certain degree of aggregation. Therefore SA@S–Fe NPs/PS technology can effectively degrade soil TBBPA, maintain soil fertility, curb the migration of heavy metals, and environmental risks.

Selective hydroxylation of benzene to phenol via C[sbnd]H activation over mesoporous Fe2O3-TiO2 using H2O2

The omnipresence of CH bonds in organic molecules enamors chemists for the functionalization of CH bonds towards value-added molecular scaffolds. Mesoporous Fe2O3-TiO2 mix-oxide catalyst has been successfully synthesized via a triblock-copolymer (P123) mediated sol-gel method and catalytically tested in selective hydroxylation of benzene. The as-synthesized catalysts were comprehensively characterized by powder XRD, Raman spectroscopy, FT-IR, N2-physisorption, FESEM, HRTEM, XPS, and NH3-TPD techniques. The physicochemical characterizations evidence that Fe(III) ions incorporate into the pure anatase TiO2 lattice framework and the crystallite size decreases as iron concentration increases. The XPS analyses confirm the Fe3+ state (BE 710.3 eV) in Fe-O-Ti with a peak at 712.1 eV for Fe3+ of Fe2O3. The NH3-TPD results show that the 5 wt% Fe-TiO2 has a higher total acidity of 105 µmol/g. Interestingly, a further increase in iron amount decreases the total acidity. Herein, we observe that the surface acidity directs the selectivity towards phenol. The effect of different reaction parameters was carefully investigated. Under the optimized conditions, 5% Fe-TiO2 with notified strong acid sites gives a higher phenol yield of 31.2% with > 99% selectivity; moreover, the catalyst is reusable at least four times.

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.

Synthesis of the Hierarchical TS-1 Using TritonX Homologues for Hydroxylation of Benzene

The hydrothermal approach was used to effectively synthesis hierarchical TS-1 utilizing the green and inexpensive surfactant TritonX homologues with varying amounts of ethylene oxide groups. The textural property of obtained materials can be modulated by varying the number of ethylene oxide groups of the TritonX homologues. The mesoporous size of hierarchical TS-1 depends on the micelles size of TritonX homologues. The synthesized samples have significant intracrystalline mesopores with a pore size range of 3.5–4.5 nm. The impact of various ethylene oxide group counts of TritonX homologous on the structure, texture properties, and titanium species was investigated using a variety of characterization methods. The hydroxylation of benzene with the H2O2 as oxidizer was used to investigate the catalytic properties of hierarchical TS-1. The catalytic properties and stability of the resulting materials were noticeably improved in the hydroxylation of benzene in comparison with the traditional TS-1.

Highly Dispersed Vanadia Anchored on Protonated g-C3N4 as an Efficient and Selective Catalyst for the Hydroxylation of Benzene into Phenol

The direct hydroxylation of benzene is a green and economical-efficient alternative to the existing cumene process for phenol production. However, the undesired phenol selectivity at high benzene conversion hinders its wide application. Here, we develop a one-pot synthesis of protonated g-C3N4 supporting vanadia catalysts (V-pg-C3N4) for the efficient and selective hydroxylation of benzene. Characterizations suggest that protonating g-C3N4 in diluted HCl can boost the generation of amino groups (NH/NH2) without changing the bulk structure. The content of surface amino groups, which determines the dispersion of vanadia, can be easily regulated by the amount of HCl added in the preparation. Increasing the content of surface amino groups benefits the dispersion of vanadia, which eventually leads to improved H2O2 activation and benzene hydroxylation. The optimal catalyst, V-pg-C3N4-0.46, achieves 60% benzene conversion and 99.7% phenol selectivity at 60 oC with H2O2 as the oxidant.

Direct Hydroxylation of Benzene with Hydrogen Peroxide Using Fe Complexes Encapsulated into Mesoporous Y-Type Zeolite.

Mesoporous Y-type zeolite (MYZ) was prepared by an acid and base treatment of commercial Y-type zeolite (YZ). The mesopore volume of MYZ was six times higher than that of YZ. [Fe(terpy)2]2+ complexes encapsulated into MYZ and YZ with different Fe contents (Fe(X)L-MYZ and Fe(X)L-YZ; X is the amount of Fe) were prepared and characterized. The oxidation of benzene with H2O2 using Fe(X)L-MYZ and Fe(X)L-YZ catalysts was carried out; phenol was selectively produced with all Fe-containing zeolite catalysts. As a result, the oxidation activity of benzene increased with increasing iron complex content in the Fe(X)L-MYZ and Fe(X)L-YZ catalysts. The oxidation activity of benzene using Fe(X)L-MYZ catalyst was higher than that using Fe(X)L-YZ. Furthermore, adding mesopores increased the catalytic activity of the iron complex as the iron complex content increased.