Baeyer–Villiger oxidation of cyclic ketones with aqueous hydrogen peroxide catalyzed by transition metal oxides

The Baeyer–Villiger oxidation of cyclic ketones to the corresponding lactones using aqueous hydrogen peroxide as an oxidant over transition metal oxides was investigated. MoO₃ and WO₃ were found to exhibit higher catalytic activity than TiO₂, Fe₂O₃, Co₃O₄, ZnO and ZrO₂. The high catalytic activity was attributed to the interaction of MoO₃/H₂O₂ and WO₃/H₂O₂. Additionally, the reaction mechanism on MoO₃ and WO₃ was proposed.     

Effective Baeyer–Villiger oxidation of ketones over germanosilicates

Germanosilicates with various topologies (UTL, BEC, UWY, IWR) serve as efficient heterogeneous catalysts for the Baeyer–Villiger oxidation of ketones. The tetrahedrally coordinated Ge ions in germanosilicates exhibited Lewis acidity, and acted as the active sites for converting ketones to corresponding lactones effectively.     

Highly efficient and reusable Cu-MCM-41 catalyst for the Baeyer–Villiger oxidation of cyclohexanone

A series of Cu-MCM-41 with different Cu contents were successfully synthesized by the direct hydrothermal (DHT) method and evaluated in the Baeyer–Villiger oxidation of cyclohexanone, using only 2 molar equiv of benzaldehyde as sacrificial agents. High conversion (99.0%) of cyclohexanone and ε-caprolactone selectivity (100%) were detected over Cu-MCM-41 (23) within 3 h. Various physical–chemical characterizations, including BET, XRD, UV–vis and H₂-TPR, revealed that isolated Cu^2 + species in the MCM-41 framework were responsible for the catalytic activities. This catalyst could be reused for three times without discernible loss in its activity and selectivity.     

Highly active InOx/TUD-1 catalyst towards Baeyer–Villiger oxidation of cyclohexanone using molecular oxygen and benzaldehyde

InOx/TUD-1 is prepared by sol–gel method and characterized by different techniques. On the basis of different characterization results it is found that spongy porous InOx/TUD-1 (In/Si = 8/100) matrix contains small crystallite of indium oxide in + 3 oxidation state. InOx/TUD-1 (In/Si = 8/100) catalyst shows good catalytic results for Baeyer–Villiger oxidation of cyclic ketones using molecular oxygen and sacrificial reagent benzaldehyde. The cyclohexanone conversion was found 100% with ε-caprolactone selectivity 100% using polar aprotic solvents e.g. dichloroethane, acetonitrile and benzonitrile in the presence of molecular oxygen.     

Fabrication of a novel ZnO–CoO/rGO nanocomposite for nonenzymatic detection of glucose and hydrogen peroxide

Herein, a novel nanocomposite of binary ZnO–CoO nanoparticles loaded on the graphene nanosheets (ZnO–CoO/rGO) has been successfully constructed via a facile, economical and two–step process. The obtained ZnO–CoO/rGO hybrids with high electrical conductivity and abundant active sites, could be modified on a glassy carbon electrode to detect glucose and H₂O₂ multi–functionally. The fabricated biosensor exhibits wide linear range for glucose (10 μM to 11.205 mM) and H₂O₂ (25 μM to 11.1 mM), and their corresponding sensitivity are 168.7 μA mM^?1 cm^?2 and 183.3 μA mM^?1 cm^?2. The limits of detection are 1.3 μM and 0.44 μM for the oxidation of glucose and the reduction of H₂O₂, respectively. Furthermore, remarkable selectivity, long–term stability and outstanding reproducibility of the non–enzyme biosensor prove that ZnO–CoO/rGO hybrids are the promising candidate in practical applications.     

Baeyer–Villiger oxidation of cyclohexanone catalyzed by cordierite honeycomb washcoated with Mg–Sn–W composite oxides

In this work, a series of Mg–Sn–W oxide powder catalysts with different tungsten oxide contents(0, 15 wt% and 30 wt%) were prepared and washcoated on cordierite honeycomb monoliths to produce monolithic catalysts,which were tested for the Baeyer–Villiger oxidation of cyclohexanone. The obtained monolithic catalysts,which combined the advantages of both homogeneous and heterogeneous catalysts, showed high catalytic efficiency and overcame the problems of product separation that occurred in the homogeneous catalytic process.SEM and EDX tests showed that the catalytic coating, with a thickness of approximately 20 μm, was compact and homogeneous, and an enlarged BET surface area was indicated by N_2 adsorption–desorption compared with the bare cordierite honeycomb. The chemical properties on the catalytic surface of the powder and monolithic catalysts were characterized by XPS, which indicated the tin and tungsten on the catalysts exhibited their full oxide states and presented mainly as stannate and tungstate, as confirmed by XRD and FTIR characterizations.Moreover, the catalytic activity test indicated that the tungsten content of the catalysts played an important role in catalytic efficiency and that monolithic catalysts were produced without obvious catalytic activity loss compared with the corresponding powders.(M)W30, which exhibited excellent mechanical stability and maintained high activity after recycling three times, was the optimal catalyst, showing a high selectivity that exceeded 86%and a conversion above 64%. Therefore, the structured Mg–Sn–W oxide catalysts have great potential for application in practical production.     

Green synthesized Au–Ag bimetallic nanoparticles modified electrodes for the amperometric detection of hydrogen peroxide

Simple and eco-friendly electro deposition method was employed for the fabrication of Au–Ag bimetallic nanoparticles modified glassy carbon electrode. Nano Au–Ag film modified glassy carbon electrode surface morphology has been examined using atomic force microscopy. Electrodeposited Au–Ag bimetallic nanoparticles were found in the average size range of 15–50 nm. The electrochemical investigations of nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film have been carried out using cyclic voltammetry and electrochemical impedance spectroscopy. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion film modified glassy carbon electrode holds the good electrochemical behavior and stability in pH 7.0 phosphate buffer solutions. The nano Au–Ag/1-butyl-3-methylimidazolium tetrafluoroborate-nafion modified glassy carbon electrode was successfully employed for the detection of H₂O₂ in the linear range of 1–250 μM in lab samples, and 1 × 10⁻³–2 × 10⁻² M in real samples, respectively.     

Preparation of Ag–Cu bimetallic dendritic nanostructures and their hydrogen peroxide electroreduction property

In this work, dendritic silver–copper (Ag–Cu) nanostructures were synthesised on a copper foil by electrodeposition and subsequently galvanic displacement reaction without any surfactant. The crystalline nature of the nanostructures was examined by X-ray diffraction, and the morphology of the material was investigated by field-emission scanning electron microscopy. The applied potential, displacement reaction time, and silver nitrate solution concentration exerted different effects on the nanoparticle shape. And a possible growth mechanism of the Ag–Cu dendrites was proposed based on the experimental results. The electrochemical properties of the Ag–Cu dendrite-modified electrode were characterised by linear sweep voltammetry. The reduction peak potential of hydrogen peroxide (H₂O₂) was about ?0.25 V (vs. a saturated calomel electrode), which indicated that the as-synthesised Ag–Cu dendrites had favourable electroreduction activity towards hydrogen peroxide. At the same time, we found that the solution pH also affected the electrocatalytic ability of the dendrites for H₂O₂ reduction, which was important for the design of a NaBH₄–H₂O₂ battery.     

Pd–Ru/C as the electrocatalyst for hydrogen peroxide reduction

Pd–Ru, Pd and Ru nanoparticles supported on Vulcan XC-72 carbon were prepared by chemical reduction of PdCl₂ and/or RuCl₃ in aqueous solution using NaBH₄ as the reducing agent. Transmission electron microscopy measurements showed that Pd–Ru particles were uniformly dispersed on carbon. The particle size of Pd–Ru is around 5–9 nm. X-ray diffraction analysis indicated that Ru formed alloy with Pd in Pd–Ru/C catalyst. The electroreduction of hydrogen peroxide on Pd–Ru/C, Pd/C and Ru/C in H₂SO₄ solution was examined by linear sweep voltammetry and chronoamperometry measurements. Results revealed that Pd–Ru/C catalyst exhibited higher electrocatalytic activity for hydrogen peroxide reduction than Pd/C and Ru/C. All the catalysts showed good stability for hydrogen peroxide electroreduction in H₂SO₄ electrolyte.     

Aureobasidium subglaciale F134 is a bifunctional whole-cell biocatalyst for Baeyer–Villiger oxidation or selective carbonyl reduction controllable by temperature

The microbial production of either ester/lactones or enantio-enriched alcohols through Baeyer–Villiger oxidation or stereoselective reduction of ketones, respectively, is possible by using whole cells of A. subglaciale F134 as a bifunctional biocatalyst. The chemoselective pattern of acetophenone biotransformation catalyzed by these cells can be regulated through reaction temperature, directing the reaction either towards oxidation or reduction products. The Baeyer–Villiger oxidation activity of A. subglaciale F134 whole cells is particularly dependent on reaction temperature. Acetophenone was transformed efficiently to phenol via the primary Baeyer–Villiger product phenyl acetate at 20 °C after 48 h with 100% conversion. In contrast, at 35 °C, enantio-enriched (S)-1-phenylethanol was obtained as the sole product with 64% conversion and 89% ee. In addition, A. subglaciale F134 cells also catalyze the selective reduction of various structurally different aldehydes and ketones to alcohols with 40% to 100% yield, indicating broad substrate spectrum and good enantioselectivity in relevant cases. Our study provides a bifunctional biocatalyst system that can be used in Baeyer–Villiger oxidation as well as in asymmetric carbonyl reduction, setting the stage for future work concerning the identification and isolation of the respective enzymes.     

Solvent-free Baeyer–Villiger oxidation with H2O2 as oxidant catalyzed by multi-SO3H functionalized heteropolyanion-based ionic hybrids

Three novel multi-SO₃H functionalized heteropolyanion-based ionic hybrids were synthesized and characterized, which as heterogeneous catalysts for Baeyer–Villiger oxidation using 35% aqueous H₂O₂ as oxidant show high catalytic activity under solvent-free conditions, the target lactones were obtained with yields of 69% to 88% in 3 h at 50 °C. Three ionic hybrids could be recovered readily and their catalytic activity almost completely retained after ten recycles.     

The Catalytic Baeyer–Villiger Oxidation of Cyclohexanone to ε-Caprolactone over Stibium-containing Hydrotalcite

A series of hydrotalcite-like compounds were prepared under microwave irradiation, which were used to catalyze the Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone with hydrogen peroxide as oxidant. The results show that stibium-containing hydrotalcite (Sb-HTL) has good catalytic properties in the reaction. In the Baeyer–Villiger oxidation of cyclohexanone to ε-caprolactone with H₂O₂ catalyzed by Sb-HTL, the effects of reaction time, reaction temperature, amount of catalyst and H₂O₂/cyclohexanone molar ratio are also investigated in details. It is shown the cyclohexanone conversion and ε-caprolactone selectivity can reach 79.15 and 93.84%, respectively, under the optimum reaction conditions. Furthermore, Sb-HTL can be reused for six times without obvious loss of activity and selectivity. Therefore, Sb-HTL is reusable and would be a promising catalyst for the Baeyer–Villiger oxidation using green and cheap oxidants like hydrogen peroxide instead of peroxycarboxylic acids.     

Effect of Pd loading and precursor on the catalytic performance of Pd/WO3–ZrO2 catalysts for selective oxidation of ethylene

The structure and properties of Pd/WO₃–ZrO₂ (W/Zr = 0.2) catalysts with different Pd loadings and precursors were investigated. The results indicate that Pd/WO₃–ZrO₂ prepared from a PdCl₂ precursor was optimum for high activity and selectivity. Moreover, ethylene conversion increased with the Pd loading. The structure and nature of the catalysts were characterized using X-ray diffraction, BET N₂ adsorption, H₂ temperature-programmed reduction and H₂ pulse adsorption techniques. The results reveal that the higher catalytic performance of Pd/WO₃–ZrO₂ prepared from PdCl₂ could be related to the formation of polytungstate species and the existence of well-dispersed Pd particles.     

MgO/SnO2/WO3 as catalysts for synthesis of ε-caprolactone over oxidation of cyclohexanone with peracetic acid

Different Mg/Sn/W mixed oxides prepared by precipitation were used as catalysts in the Baeyer–Villiger oxidation of cyclohexanone with a mixture of 50% hydrogen peroxide and acetic acid as oxidant. The Mg/Sn/W oxide obtained by precipitation from NH₃·H₂O was found to be the catalyst providing the highest yield of ε-caprolactone and initial catalytic activity among all samples.     

Kinetic study and hydrogen peroxide consumption of phenolic compounds oxidation by Fenton’s reagent

Synthetic solutions of phenol, o-, m- and p-cresol were oxidised by using Fenton’s reagent. The application of substoichiometric dosage of H₂O₂ led to the formation of intermediate compounds, continuing later the oxidation to complete oxidation. An important objective was to analyze the effect of hydrogen peroxide dosage applied and the reaction pH together with the iron oxidation state on the degradation level. A kinetic model was derived from a reaction mechanism postulated which was used to analyze the results of the experiments. Another aim was to analyze the hydrogen peroxide consumption. Noteworthy results include an increase in oxidant consumption to intensify phenol removal. Furthermore, oxidant consumption was analyzed through the ratio H₂O₂ to phenol removed and the average specific rate of removal (ASRR). By analyzing these two parameters it has been possible to ascertain the most favorable strategy for an efficient application of H₂O₂.