Oxidation Of Benzene Research Articles

Benzene Oxidation in Air by an Amine-Functionalized Metal-Organic Framework-Derived Carbon- and Nitrogen-Loaded Zirconium Dioxide-Supported Platinum Catalyst.

To learn more about the behavior of amine (NH2)-functionalized metal-organic framework (MOF)-derived noble metal catalysts in the removal of aromatic volatile organic compounds in air, benzene oxidation at low temperatures has been investigated using 0.2-, 0.8-, and 1.5%-platinum (Pt)/Universitetet i Oslo (UiO)-66-NH2. The benzene conversion (XB) of x%-Pt/UiO-66-NH2-R under dry conditions (175 °C) was 23% (x = 0.2%) < 52% (x = 0.8%) < 100% (x = 1.5%): 'R' suffix denotes reduction pretreatment using a hydrogen (10 vol %) and nitrogen mixture at 300 °C for the generation of metallic Pt (Pt0) sites and simultaneous partial MOF decomposition into carbon- and nitrogen-loaded zirconium dioxide. The prominent role of reduction pretreatment was apparent in benzene oxidation as 1.5%-Pt/UiO-66-NH2 did not exhibit catalytic activity below 175 °C (dry condition). The promotional role of moisture in benzene oxidation by 1.5%-Pt/UiO-66-NH2-R was evident with a rise in the steady-state reaction rate (r) at 110 °C (21 kPa molecular oxygen (O2)) from 1.3 × 10-3 to 5.0 × 10-3 μmol g-1 s-1 as the water (H2O) partial pressure increased from 0 to 1.88 kPa. In contrast, the activity was lowered with increasing RH due to catalyst poisoning by excess moisture (r (110 °C) of 6.6 × 10-04 μmol g-1 s-1 at 2.83 kPa H2O (21 kPa O2)). Kinetic modeling suggests that XB proceeds through the Langmuir-Hinshelwood mechanism on the Pt/UiO-66-NH2-R surface (dissociative O2 chemisorption and the involvement of two oxygen species in benzene oxidation). According to the density functional theory simulation, the carbon and nitrogen impurities are to make the first XB step (i.e., hydrogen migration from the benzene molecule to the substrate) energetically favorable. The second hydrogen atom from the benzene molecule is also extracted effectively, while the oxygen derived from O2 facilitates further XB. The Pt0 sites dissociate the O2 and H2O molecules, while the product of the latter, i.e., free hydrogen and hydroxyl, makes the subsequent XB steps energetically favorable.

Dual roles of the inorganic aqueous phase on secondary organic aerosol growth from benzene and phenol

Abstract. Benzene, emitted from automobile exhaust and biomass burning, is ubiquitous in ambient air. Benzene is a precursor hydrocarbon (HC) that forms secondary organic aerosol (SOA), but its SOA formation mechanism is not well studied. To accurately predict the formation of benzene SOA, it is important to understand the gas mechanisms of phenol, which is one of the major products formed from the atmospheric oxidation of benzene. Laboratory data presented herein highlight the impact of the aqueous phase on SOA generated through benzene and phenol oxidation. The roles of the aqueous phase consist of (1) suppression of the aging of hydrocarbon and (2) conventional acid-catalyzed reactions in the inorganic phase. To explain this unusual effect, it is hypothesized that a persistent phenoxy radical (PPR) effectively forms via a heterogeneous reaction of phenol and phenol-related products in the presence of wet inorganic aerosol. These PPR species are capable of catalytically consuming ozone during an NOx cycle and negatively influencing SOA growth. In this study, explicit gas mechanisms were derived to produce the oxygenated products from the atmospheric oxidation of phenol or benzene. Gas mechanisms include the existing Master Chemical Mechanism (MCM v3.3.1), the reaction path for peroxy radical adducts originating from the addition of an OH radical to phenols forming low-volatility products (e.g., multi-hydroxy aromatics), and the mechanisms to form heterogeneous production of PPR. The simulated gas products were classified into volatility- and reactivity-based lumped species and incorporated into the Unified Partitioning Aerosol Reaction (UNIPAR) model that predicts SOA formation via multiphase reactions of phenol or benzene. The predictability of the UNIPAR model was examined using chamber data, which were generated for the photooxidation of phenol or benzene under controlled experimental conditions (NOx levels, humidity, and inorganic seed types). The SOA formation from both phenol and benzene still increased in the presence of wet inorganic seed because of the oligomerization of reactive organic species in the aqueous phase. However, model simulations show a significant suppression of ozone, the oxidation of phenol or benzene, and SOA growth compared with those without PPR mechanisms. The production of PPR is accelerated in the presence of acidic aerosol and this weakens SOA growth. In benzene oxidation, up to 53 % of the oxidation pathway is connected to phenol formation in the reported gas mechanism. Thus, the contribution of PPR to gas mechanisms is less than that of phenol. Overall, SOA growth in phenol or benzene is negatively related to NOx levels in the high-NOx region (HC ppbC / NOx ppb &lt; 5). However, the simulation indicates that the significance of PPR rises with decreasing NOx levels. Hence, the influence of NOx levels on SOA formation from phenol or benzene is complex under varying temperature and seed type conditions. Adding the comprehensive reaction of phenolic compounds will improve the prediction of SOA formation from aromatic HCs due to the missing mechanisms in the current air quality model.

Identification of New Hepatic Metabolites of Miconazole by Biological and Electrochemical Methods Using Ultra-High-Performance Liquid Chromatography Combined with High-Resolution Mass Spectrometry.

The main objective of this study was to investigate the metabolism of miconazole, an azole antifungal drug. Miconazole was subjected to incubation with human liver microsomes (HLM) to mimic phase I metabolism reactions for the first time. Employing a combination of an HLM assay and UHPLC-HRMS analysis enabled the identification of seven metabolites of miconazole, undescribed so far. Throughout the incubation with HLM, miconazole underwent biotransformation reactions including hydroxylation of the benzene ring and oxidation of the imidazole moiety, along with its subsequent degradation. Additionally, based on the obtained results, screen-printed electrodes (SPEs) were optimized to simulate the same biotransformation reactions, by the use of a simple, fast, and cheap electrochemical method. The potential toxicity of the identified metabolites was assessed using various in silico models.

Revisit the benzene oxidation at elevated pressure

The benzene (A1) oxidation was examined in a jet-stirred reactor (JSR) within the temperature range of 880–1010 K at 12.0 atm under both fuel lean (Φ = 0.5) and rich (Φ = 3.0) conditions. Eighteen intermediates and products were identified and quantified by gas chromatography (GC) and gas chromatograph-mass spectrometer (GC–MS). A kinetic model comprising 280 species and 1734 reactions was developed and validated against the experimental data to investigate the benzene reactions occurring at high pressure and low temperature. According to the sensitivity analysis, A1 + OH = A1- + H2O is the most promoting reaction for fuel consumption, while A1OH + O2 = A1O + HO2 and A1OH + OH = A1O + H2O exhibited the most inhibiting effects. HO2 radicals play an important role in the initial reaction temperature of A1 high-pressure oxidation, where the reaction rate of A1OH + O2 = A1O + HO2 is particularly critical. In comparison to previous works on A1 oxidation, oxygenated polycyclic aromatic hydrocarbons (OPAHs) benzofuran (C8H6O) and dibenzofuran (C12H8O) were newly measured and analyzed in this work. As one of the most important OPAHs species, the consumption pathway of C8H6O was updated to better describe the high-pressure oxidation. The C8H6O would potentially compete with A1 for molecular oxygen via the pathway A1 → A1O → C8H6O → decomposition products, and the process of decomposition enhances the oxygen depletion. Compared with previous oxidation studies at atmospheric pressure, the A1 initial reaction temperature shifted from 1000 to 950 K, and the temperature window of fuel conversion sharply reduced from 300 K to 70 K. Additionally, the model was effectively applied to predict the oxidation of A1 in a Jet-Stirred Reactor (JSR) over a wide range of pressures, from 0.46 to 12.0 atm. Furthermore, the developed model was compared with the laminar flame velocities (LBVs, ranging from 1.0 - 10.0 atm) and the ignition delay times (IDTs, ranging from 2.4 – 9.0 atm) data in the literature, and satisfactory agreement was obtained across a broad pressure range. The newly reported data and kinetic model provide helpful in further understanding the combustion mechanisms of aromatic hydrocarbon fuels.

Tuning benzene activity of cobalt-based spinel catalysts with cation substitution

Cobalt-based spinel oxides are promising low-cost catalysts for volatile organic compounds (VOCs) elimination. Herein, we prepared the cobalt-based spinel oxides (MCo2O4: M = Ni, Cu, Co, Zn) by a one-step solvothermal method to evaluate the influence of cation substitution on benzene combustion. The cation distribution on tetrahedral and octahedral sites could influence the degree of inversion in cobalt-based spinel oxides, thus achieving the regulation of Co-O bond strength. NiCo2O4 catalyst with the inverse spinel structure had the weak Co-O bond strength, which is conducive to the activation of lattice oxygen to improve the activity of benzene degradation. This work provides deep insights into the influence of the cation substitution on the cobalt-based spinel catalysts for the efficient benzene oxidation.

Highly coupled MnO2/Mn5O8 Z-scheme heterojunction modified by Co3O4 co-catalyst: An efficient and stable photocatalyst to decompose gaseous benzene

MnOx Z-scheme heterojunction exhibits a strong redox capacity, thereby it has great potential in the field of photocatalysis for gaseous benzene oxidation to address environmental pollution. However, the self-oxidation of MnOx due to the accumulation of photogenerated holes severely restricts its practical application. Herein, a highly coupled MnO2/Mn5O8 Z-scheme heterojunction modified by Co3O4 co-catalyst grown on ammoniated carbon cloth (MnOx/Co3O4@ACC) was constructed through electrodeposition and applied for efficient photocatalytic benzene degradation. The optimized MnOx/Co3O4@ACC presents high-efficient degradability, mineralization rate and high stability after 60 cycles (30 h). Co3O4 served as a hole collector to promote the extraction of photogenerated holes from the MnOx surface, suppressing the photocorrosion of MnOx. Additionally, the by-product CO was more easily absorbed and activated on MnOx/Co3O4@ACC surface due to the introduction of Co3O4. The electrodeposition-photocatalysis strategy developed in this work shows great application prospects for environmental contaminant remediation.

SO2-resistant hollow carbon spheres encapsulated Pt nanoparticles for benzene oxidation

In the catalytic combustion of volatile organic compounds (VOCs) using noble metal catalysts, resistance to SO2 poisoning poses a significant challenge. To tackle this problem, Pt nanoparticle catalysts encapsulated in hollow carbon spheres (Pt@HCS catalysts) are synthesized. The Pt@HCS catalyst exhibits excellent benzene conversion, achieving 100 % conversion at 165 °C under an air velocity of 20,000 mL/(g h). Compared to the conventional supported Pt/HCS catalyst, the Pt@HCS catalyst demonstrates a significantly improved resistance to SO2 poisoning. In the presence of 25 ppm SO2, the Pt@HCS catalyst is capable of maintaining a 100 % benzene conversion rate within 24 h, whereas the conversion rate of Pt/HCS drops substantially to approximately 52 %. It is confirmed that the hollow porous structure provided a larger specific surface area and more adsorption sites, thereby facilitating benzene oxidation. More importantly, in situ DRIFTS reveals that the adsorption and desorption processes of SO2, along with the generation of substances like SO32−, are strictly limited to the surface of the carbon shell, thereby preserving the integrity of the internal reaction environment. Multiple characterizations combined with density functional theory (DFT) have demonstrated a unique separation effect over Pt@HCS, whereby the hydroxyl groups on the carbon shell preferentially capture SO2 while allowing benzene molecules to enter the cavities of the catalyst. In this way, any internal ingress of SO2 and competition with benzene for Pt adsorption is effectively avoided. This study offers a potential solution to enhance the performance of noble metal catalysts in the presence of sulfur compounds.

Pt on Atomic-Layered WO3 Islands: Electronic Tuning of Platinum-Tungsten Heterostructures for Highly Efficient Low-Temperature VOC Combustion.

Adjusting the electronic state of noble metal catalysts on a nanoscale is crucial for optimizing the performance of nanocatalysts in many important environmental catalytic reactions, particularly in volatile organic compound (VOC) combustion. This study reports a novel strategy for optimizing Pt catalysts by modifying their electronic structure to enhance the electron density of Pt. The research illustrates the optimal 0.2Pt-0.3W/Fe2O3 heterostructure with atomic-thick WO3 layers as a bulking block to electronically modify supported Pt nanoparticles. Methods such as electron microscopy, X-ray photoelectron spectroscopy, and in situ Fourier transform infrared spectroscopy confirm Pt's electron-enriched state resulting from electron transfer from atomic-thick WO3. Testing for benzene oxidation revealed enhanced low-temperature activity with moderate tungsten incorporation. Kinetic and mechanistic analyses provide insights into how the enriched electron density benefits the activation of oxygen and the adsorption of benzene on Pt sites, thereby facilitating the oxidation reaction. This pioneering work on modifying the electronic structure of supported Pt nanocatalysts establishes an innovative catalyst design approach. The electronic structure-performance-dependent relationships presented in this study assist in the rational design of efficient VOC abatement catalysts, contributing to clean energy and environmental solutions.

Oxidation of Benzene to Phenol By Nitrous Oxide on Me-ZSM-5-Zeolites with a Low Concentration of Active Sites: Role of Single Active Sites

Oxidation of Benzene to Phenol By Nitrous Oxide on Me-ZSM-5-Zeolites with a Low Concentration of Active Sites: Role of Single Active Sites

Effect of Interaction between Pt and Different Crystalline Phases of TiO2 on Benzene Oxidation

To evaluate the effects of different TiO2 crystalline phases on the catalytic oxidation performance of benzene on Pt-loaded TiO2 catalysts, physicochemical examinations were conducted using several spectroscopic and analytical techniques. Obvious effects on the valence state and morphology of Pt were exhibited by different crystalline phases. The rutile phase favored the formation of specific Pt(111) crystal faces, which enhanced the amount of surface-active oxygen species. Moreover, the àPt-O-Ti species was formed between Pt4+ and Ti at the edge of the Pt nanoparticles, promoting both electron flow and the transfer of reactive oxygen species, thus accounting for catalytic activity.

Catalytic Oxidation of Benzene over Atomic Active Site AgNi/BCN Catalysts at Room Temperature.

Benzene is the typical volatile organic compound (VOC) of indoor and outdoor air pollution, which harms human health and the environment. Due to the stability of their aromatic structure, the catalytic oxidation of benzene rings in an environment without an external energy input is difficult. In this study, the efficient degradation of benzene at room temperature was achieved by constructing Ag and Ni bimetallic active site catalysts (AgNi/BCN) supported on boron-carbon-nitrogen aerogel. The atomic-scale Ag and Ni are uniformly dispersed on the catalyst surface and form Ag/Ni-C/N bonds with C and N, which were conducive to the catalytic oxidation of benzene at room temperature. Further catalytic reaction mechanisms indicate that benzene reacted with ·OH to produce R·, which reacted with O2 to regenerate ·OH. Under the strong oxidation of ·OH, benzene was oxidized to form alcohols, carboxylic acids, and eventually CO2 and H2O. This study not only significantly reduces the energy consumption of VOC catalytic oxidation, but also improves the safety of VOC treatment, providing new ideas for the low energy consumption and green development of VOC treatment.

Out-of-Plane Single-Copper-Site Catalysts for Room-Temperature Benzene Oxidation.

Crafting single-atom catalysts (SACs) that possess "just right" modulated electronic and geometric structures, granting accessible active sites for direct room-temperature benzene oxidation is a coveted objective. However, achieving this goal remains a formidable challenge. Here, we introduce an innovative in situ phosphorus-immitting strategy using a new phosphorus source (phosphorus nitride, P3N5) to construct the phosphorus-rich copper (Cu) SACs, designated as Cu/NPC. These catalysts feature locally protruding metal sites on a nitrogen (N)-phosphorus (P)-carbon (C) support (NPC). Rigorous analyses, including X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS), validate the coordinated bonding of nitrogen and phosphorus with atomically dispersed Cu sites on NPC. Crucially, systematic first-principles calculations, coupled with the climbing image nudged-elastic-band (CI-NEB) method, provide a comprehensive understanding of the structure-property-activity relationship of the distorted Cu-N2P2 centers in Cu/NPC for selective oxidation of benzene to phenol production. Interestingly, Cu/NPC has shown more energetically favorable C-H bond activation compared to the benchmark Cu/NC SACs in the direct oxidation of benzene, resulting in outstanding benzene conversion (50.3 %) and phenol selectivity (99.3 %) at room temperature. Furthermore, Cu/NPC achieves a remarkable turnover frequency of 263 h-1 and mass-specific activity of 35.2 mmol g-1 h-1, surpassing the state-of-the-art benzene-to-phenol conversion catalysts to date.

Out‐of‐Plane Single‐Copper‐Site Catalysts for Room‐Temperature Benzene Oxidation

AbstractCrafting single‐atom catalysts (SACs) that possess “just right” modulated electronic and geometric structures, granting accessible active sites for direct room‐temperature benzene oxidation is a coveted objective. However, achieving this goal remains a formidable challenge. Here, we introduce an innovative in situ phosphorus‐immitting strategy using a new phosphorus source (phosphorus nitride, P3N5) to construct the phosphorus‐rich copper (Cu) SACs, designated as Cu/NPC. These catalysts feature locally protruding metal sites on a nitrogen (N)‐phosphorus (P)‐carbon (C) support (NPC). Rigorous analyses, including X‐ray absorption spectroscopy (XAS) and X‐ray photoelectron spectroscopy (XPS), validate the coordinated bonding of nitrogen and phosphorus with atomically dispersed Cu sites on NPC. Crucially, systematic first‐principles calculations, coupled with the climbing image nudged‐elastic‐band (CI‐NEB) method, provide a comprehensive understanding of the structure‐property‐activity relationship of the distorted Cu−N2P2 centers in Cu/NPC for selective oxidation of benzene to phenol production. Interestingly, Cu/NPC has shown more energetically favorable C−H bond activation compared to the benchmark Cu/NC SACs in the direct oxidation of benzene, resulting in outstanding benzene conversion (50.3 %) and phenol selectivity (99.3 %) at room temperature. Furthermore, Cu/NPC achieves a remarkable turnover frequency of 263 h−1 and mass‐specific activity of 35.2 mmol g−1 h−1, surpassing the state‐of‐the‐art benzene‐to‐phenol conversion catalysts to date.

The promotion mechanism of Mn on the catalytic degradation of benzene by H2O2 on Cu surface: The simultaneous enhancement of OH generation and benzene oxidation by ·OH

It is a promising technology to degrade benzene by using the strong oxidizing ·OH produced by H2O2 decomposition. However, in practical engineering, the low yield and utilization rate of ·OH affect the degradation effect, and the development of new catalysts is the key to solve this problem. The effects of Mn-doped on the decomposition of H2O2 on the surface of Cu (Mn-Cu) to obtain ·OH were studied by combining density functional theory, including the adsorption and decomposition characteristics of H2O2 and the ineffective consumption reaction of ·OH on the surface. At the same time, the specific reaction process between benzene and · OH on the surface was studied, and the effectiveness improvement of various reactions on the surface of Mn-Cu was analyzed in detail. It is found that the charge transfer between Mn and Cu forms positive and negative charge centers on the surface, the O-O bond break of H2O2 molecules that promote adsorption on the surface occurs homolysis, and has a significant inhibitory effect on the ineffective consumption reaction between ·OH and H2O2 molecules and ·HO2, thus improving the yield and utilization of ·OH. At the same time, the reaction energy barrier between ·OH and benzene was significantly reduced, the energy barrier of the first stage of degradation was reduced from 206.86 kJ/mol to 27.02 kJ/mol, and the degradation efficiency of benzene was greatly improved. And the effect improvement was verified through degradation experiments. The degradation rate of Mn-Cu surface is higher than that of Cu surface at all stages, and the final degradation rate can reach about 89%. By clarifying the above reaction mechanism, it provides theoretical support for the development of new catalysts.

Gas-phase oxidation of benzene using Cu-loaded MFI binderless zeolite compacts

Phenols are essential raw materials for various fields, and several studies have focused on their synthesis. The development of an efficient one-step synthetic method for the industrial production of phenols is highly important in terms of cost, energy, and environmental impact. In this study, we investigated the formation of phenols via the gas-phase oxidation of benzene using copper-loaded MFI zeolite compacts prepared via a binderless zeolite synthetic method. The catalytic activity of the zeolite in the gas-phase phenol one-step synthetic reaction was investigated, in addition to the effect of benzene diffusion in the molded zeolite and the reaction due to water vapor addition to the reaction gas. The results showed that the activity of the copper-loaded MFI zeolite compacts was almost equivalent to that of powdered copper-loaded MFI zeolites. An effect of diffusion was observed on the external boundary film diffusion where the linear velocity was low. However, no effect of diffusion or internal diffusion was observed in the area where the linear velocity was high. Furthermore, the addition of water vapor to the reaction gas suppressed the decrease in phenol formation activity due to the formation of coke on the catalyst surface.

Effect of Ligands within Vanadium Complex Encapsulated in Y Zeolite Catalysts on Liquid-phase Benzene Oxidation

Effect of Ligands within Vanadium Complex Encapsulated in Y Zeolite Catalysts on Liquid-phase Benzene Oxidation

Ultrathin LayCoOx Nanosheets with High Porosity Featuring Boosted Catalytic Oxidation of Benzene: Mechanism Elucidation via an Experiment-Theory Combined Paradigm.

Designing transition-metal oxides for catalytically removing the highly toxic benzene holds significance in addressing indoor/outdoor environmental pollution issues. Herein, we successfully synthesized ultrathin LayCoOx nanosheets (thickness of ∼1.8 nm) with high porosity, using a straightforward coprecipitation method. Comprehensive characterization techniques were employed to analyze the synthesized LayCoOx catalysts, revealing their low crystallinity, high surface area, and abundant porosity. Catalytic benzene oxidation tests demonstrated that the La0.029CoOx-300 nanosheet exhibited the most optimal performance. This catalyst enabled complete benzene degradation at a relatively low temperature of 220 °C, even under a high space velocity (SV) of 20,000 h-1, and displayed remarkable durability throughout various catalytic assessments, including SV variations, exposure to water vapor, recycling, and long time-on-stream tests. Characterization analyses confirmed the enhanced interactions between Co and doped La, the presence of abundant adsorbed oxygen, and the extensive exposure of Co3+ species in La0.029CoOx-300 nanosheets. Theoretical calculations further revealed that La doping was beneficial for the formation of oxygen vacancies and the adsorption of more hydroxyl groups. These features strongly promoted the adsorption and activation of oxygen, thereby accelerating the benzene oxidation processes. This work underscores the advantages of doping rare-earth elements into transition-metal oxides as a cost-effective yet efficient strategy for purifying industrial exhausts.

Oxidative two-state photoreactivity of a manganese(IV) complex using near-infrared light.

Highly reducing or oxidizing photocatalysts are a fundamental challenge in photochemistry. Only a few transition metal complexes with Earth-abundant metal ions have so far advanced to excited state oxidants. All these photocatalysts require high-energy light for excitation, and their oxidizing power has not been fully exploited due to energy dissipation before reaching the photoactive state. Here we demonstrate that the complex [Mn(dgpy)2]4+, based on Earth-abundant manganese and the tridentate 2,6-diguanidylpyridine ligand (dgpy), evolves to a luminescent doublet ligand-to-metal charge transfer (2LMCT) excited state (1,435 nm, 0.86 eV) with a lifetime of 1.6 ns after excitation with low-energy near-infrared light. This 2LMCT state oxidizes naphthalene to its radical cation. Substrates with extremely high oxidation potentials up to 2.4 V enable the [Mn(dgpy)2]4+ photoreduction via a high-energy quartet 4LMCT excited state with a lifetime of 0.78 ps, proceeding via static quenching by the solvent. This process minimizes free energy losses and harnesses the full photooxidizing power, and thus allows oxidation of nitriles and benzene using Earth-abundant elements and low-energy light.

Generation and Reactivity of μ-1,2-Peroxo CuIICuII and Bis-μ-oxo CuIIICuIII Species and Catalytic Hydroxylation of Benzene to Phenol with Hydrogen Peroxide.

Tetradentate-N4 ligands stabilize dinuclear {CuII(μ-1,2-peroxo)CuII} and {CuIII(μ-O)2CuIII} species, and CuII complexes of these ligands were reported to catalyze the oxidation of benzene with H2O2. Here, we report {CuII(μ-1,2-peroxo)CuII} and {CuIII(μ-O)2CuIII} intermediates of dinucleating bis(tetradentate-N4) ligands depending on the absence or presence of 6-methyl substituents on the terminal pyridine donors, respectively, generated either from {CuICuI} precursors with O2 or from {CuIICuII} precursors with H2O2 and NEt3. Both intermediates are not stable even at low temperatures, but they show no electrophilic HAT reactivity with DHA. Catalytic investigations on the hydroxylation of benzene with excess H2O2 between 30 and 50 °C indicate that both radical-based and {Cu2On}-based mechanisms depend strongly on the catalytic conditions. In the presence of a radical scavenger, TONs of ∼920/∼720 have been achieved without/with the 6-methyl group of the ligand. Although {CuII(μ-OH)CuII} reacts with excess H2O2 at -40 °C to {CuII(OOH)}2 species, these are only stable for seconds at 20 °C and cannot account for catalytic oxidations over a period of 24 h at 30-50 °C.

Promoted catalytic oxidation of benzene over Mn-Ni solid solutions: Effect of metal oxygen bond parameters

In this work, Mn-Ni solid solutions were obtained by doping Ni into MnOx via solution combustion synthesis and the resulting catalysts were then applied to benzene oxidation. Various characterizations revealed that Ni doping changed the metal oxygen bond parameters, such as coordination numbers (CNs) and bond length. Both Mn-O and Ni-O bonds in Mn-Ni solid solutions exerted reduced CNs, while the bond length of Mn-O bonds was extended, making the oxygen species more chemically reactive., which further improved physicochemical properties (such as reducibility, oxygen mobility, surface active oxygen species etc.) and catalytic performance. Remarkably, the solid solutions with a Mn/Ni molar ratio of 4:1 (named Mn4Ni1) showed Mn-O and Ni-O bonds with lower CNs and longer bond lengths, which enhanced the activity and mobility of oxygen species, reducibility and chemisorption capacity of benzene. Therefore, Mn4Ni1 demonstrated optimal benzene oxidation activity and showed the lowest T90 (192 °C). The potential reaction mechanism was proposed according to the analysis results of C6H6-TPSR and in-situ FTIR. Furthermore, promoted oxidation of benzene and phenolate species on Mn4Ni1 could inhibit accumulation of intermediates and avoid catalyst poisoning and deactivation. This strategy shed light to the design of catalysts in environmental catalysis and thermal catalysis.