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.     

The multifunctional mesoporous Sn–Cu–Ti catalysts for the B–V oxidation of cyclohexanone by molecular oxygen

The multifunctional three-component mesoporous Sn–Cu–Ti samples were successfully prepared by a facile one-pot AcHE method and characterized by XRD, N₂ sorption, ICP, FT-IR, UV–vis, SEM and TEM techniques, and their catalytic performances were carried out in the B–V oxidation of cyclohexanone by molecular oxygen. The results show that both tin and copper species can homogeneously incorporated in the crystalline framework of mesoporous anatase TiO₂, where tin species as the active sites would increase the Lewis acidity and the oxidation of benzaldehyde as pro-oxygenic agent would be promoted by the introduction of little copper species resulting in the improving catalytic performance. The prepared 15Sn–3Cu–Ti catalyst shows higher yield of ε-caprolactone than other catalysts and exhibits excellent catalytic stability even after repeated reaction for five times without any further treatment. The outstanding catalytic performance for Sn–Cu–Ti catalysts could offer a valuable reference for the industrial development of B–V oxidation of cyclohexanone.     

Model bulk Mo–V–Te–O catalysts for selective oxidation of propane to acrylic acid

The crystal structures and chemical compositions of the M1 and M2 phases proposed as active and selective in propane oxidation to acrylic acid over the bulk mixed Mo–V–Te–O catalysts were investigated by the transmission electron microscopy, coupled with energy dispersive analysis of X-rays. The results revealed that the crystal structure of the M1 phase is orthorhombic with space group Pbca, lattice parameters a=21.25 Å, b=27.14 Å, c=4.03 Å and composition Mo_0.64V_0.32Te_0.1O_3.05 (Mo/V ∼2), whereas M2 is hexagonal with space group P6mm, lattice parameters a=7.10 Å, c=4.05 Å and composition Mo_1.79V_1.85Te_0.1O_11.36 (Mo/V ∼1). The M1 phase was dominant in the Mo–V–Te–O catalyst. The results obtained indicated that the bulk Mo–V–Te oxides represent a well-defined model catalytic system for the studies of the surface molecular structure-activity/selectivity relationships in propane oxidation to acrylic acid.     

Preparation optimization of multilayer-structured SnO2–Sb–Ce/Ti electrode for efficient electrocatalytic oxidation of tetracycline in water

In this study, electrodeposition and thermal decomposition were alternatively used for the fabrication of a series of novel multilayer-structured SnO₂-Sb-Ce/Ti (SSCT) electrodes, and their physiochemical and electrochemical properties were investigated for electrochemical oxidation of tetracycline (TC) in aqueous medium. Experimentally, after the SnO₂-Sb-Ce (SSC) composite was electrodeposited for 120 s on the titanium substrate in aqueous solution, the outer thermal coatings composed of SSC were synthesized by a hydrothermal method. Both influences of electrodeposition time (T_ed) and thermal decomposition time (T_td) were investigated to obtain the optimum preparation. It was found that when increasing T_ed to a certain extent a longer lifetime of electrode can be achieved, which was attributed to a more solid interlayer structure. A notable SSCT_Ted,Ttd electrode, i.e., SSCT_3,10, which was prepared through three times of 120 s' electrodeposition (T_ed=3) and ten times of thermal decomposition (T_td=10) obtained the highest oxygen evolution potential 3.141 V vs. SCE. In this selected electrode, when 10 mg·L^-1 initial TC concentration was added to this wastewater, the highest color removal efficiency and mineralization rate of TC were 72.4% and 41.6%, respectively, with an applied electricity density of 20 mA·cm^-2 and treatment time of 1 h. These results presented here demonstrate that the combined application of electrodeposition and thermal decomposition is effective in realization of enhanced electrocatalytic oxidation activity.     

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.     

Supported zirconium-based continuous-flow microreactor for effective Meerwein–Ponndorf–Verley reduction of cyclohexanone

Continuous-flow monolithic silica microreactor activated with anchored isolated zirconium species was shown to be a very convenient and efficient system for chemoselective Meerwein–Ponndorf–Verley reduction. It was shown that isolated Zr^4 + ions covalently bonded to the silica surface and terminated with isopropoxy/hydroxo ligands can be much more catalytically active than supported zirconia. Conversion of cyclohexanone approached 100% and excellent catalytic selectivity and stability were obtained in 8 cm long microreactor during 8 catalytic cycles. The microreactors also enable better control of undesired hydrolysis of highly reactive metal precursors during functionalisation of the monoliths.     

A simple and efficient oxidation system for the oxidation of alcohols utilizing Oxone® as oxidant catalyzed by polymer-supported 2-iodobenzamide

$\begin{array}{l}{\hbox{R}^1\hbox{R}^2\hbox{CHOH}} \\ {\hbox{RCH}_2\hbox{OH} }\end{array} \dynrightarrow{Oxone}{\hbox{CH}_3\hbox{CN/H}_2\hbox{O}, 70^{\circ}\hbox{C}} \begin{array}{l}{\hbox{R}^1\hbox{R}^2\hbox{CO}} \\ {\hbox{RCOOH}} \end{array} A simple and environmentally friendly procedure for the oxidation of alcohols is presented utilizing Oxone^? (2KHSO₅ · KHSO₄ · K₂ SO₄) as oxidant and polymer-supported 2-iodobenzamide as catalyst in CH₃CN/H₂O mixed solvents.     

Mode of action of oxidation‐active centres in Mo–V mixed oxides on the partial oxidation of an unsaturated aldehyde

The mode of action of the oxidation‐active centres in Mo–V mixed oxides on the selective oxidation of an unsaturated aldehyde was investigated by non‐steady‐state methods. Various oxidation‐active centres, differing in activity and selectivity, were identified by non‐steady‐state methods. In addition, the influence of the crystallinity of the Mo–V mixed oxides on the activity and selectivity properties were investigated. It was shown that, in contrast to crystalline samples, only X‐ray‐amorphous Mo–V mixed oxides contained selective oxidation centres. The measurements were used to derive a model based on the interaction of active centres with various redox properties. This revised version was published online in July 2006 with corrections to the Cover Date.     

Polyoxometalate–molybdenylacetylacetonate hybrid complex: A reusable and efficient catalyst for oxidation of alkenes with tert-butylhydroperoxide

The hybrid complex consist of molybdenylacetylacetonate complex covalently linked to a lacunary Keggin-type polyoxometalate, K₈[SiW₁₁O₃₉] (POM), was synthesized and characterized by elemental analysis, SEM, XRD, diffuse reflectance UV–Vis and FT-IR spectroscopic methods. The hybrid complex, [MoO₂(acac)–POM] (1), was used for alkene epoxidation with tert-BuOOH in 1,2-dichloroethane as solvent. The complex (1) can catalyze epoxidation of various olefins including non-activated terminal olefins. The effect of reaction parameters such as oxidant, solvent, and temperature on the epoxidation of cyclooctene was also investigated. This heterogeneous catalyst was reused several times in the oxidation of cyclooctene.     

On the oxidation–reduction kinetics of palladium

The oxidation–reduction kinetics of Pd was investigated on polycrystalline Pd foils using XPS and sputter‐depth profiling over a wide range of temperatures. The observed behavior can be explained in terms of a desorption‐controlled process at lower temperatures (T > 230° C) and a diffusion‐controlled process at higher temperatures (T > 450° C). In the intermediate range (230 < T < 450°C) a transition between the two processes is observed which gives rise to a pronounced shoulder in the reduction time trace. The interpretation is qualitatively confirmed using a simple mathematical model for a coupled bulk diffusion/surface reaction system. This revised version was published online in July 2006 with corrections to the Cover Date.     

Optimization of the photo-deposition parameters for carbon monoxide oxidation over gold–titania

In this study, gold–titania catalyst was prepared by photo-deposition method for oxidizing carbon monoxide (CO) to carbon dioxide (CO₂). Characterization and activity tests were conducted to investigate the effects of a number of control factors on CO oxidation efficiency, including the precursor pH value, the illumination mode and condition, as well as the reaction temperature. Among these, the precursor pH value was the most profound factor, followed by its interaction effect with the illumination duration. Using controlled periodic illumination mode for photo-deposition resulted in approximately 3–6% performance enhancement compared to using continuous illumination mode due to the formation of smaller gold particle sizes. Regardless the illumination modes, CO oxidation efficiency increased with the reaction temperature up to about 60°C; further increase had not guaranteed any improvement. The same trend was observed for the illumination duration factor (where there existed an optimum value). DRIFTS (Diffuse Reflectance for Infrared Fourier Transform Spectroscopy) results showed the limited reaction of chemisorbed CO with lattice oxygen of the titania support and that purging with oxygen failed to repel the reaction intermediates. Based on the design of experiments–analysis of variance analyses, the estimated best photo-deposition parameters were found to be a precursor pH value of 9, under periodic illumination mode with a frequency of 1,000?Hz and duty cycle of 0.2, for an illumination duration of 6.2?min.     

V–BaCO3 catalysts for the oxidative dehydrogenation of ethane

A new type of supported vanadium oxide catalyst V–BaCO₃, which consists of barium orthovanadate Ba₃(VO₄)₂ and BaCO₃ phases, has been used in the oxidative dehydrogenation of ethane. The catalyst with the ratio of V/Ba from 0.1 to 0.3 exhibited high catalytic activity for oxidative dehydrogenation of ethane, with particularly high activity for ethene production.     

Preparation of Mesoporous V–Ce–Ti–O for the Selective Oxidation of Methanol to Dimethoxymethane

Mesoporous V–Ce–Ti–O oxides were synthesized through the combination of sol–gel and hydrothermal methods and were characterized by different techniques. N₂ adsorption showed that the mesoporous oxides with 0–20 wt.% V₂O₅ possessed the surface areas of about 160 m² g^?1 with narrow pore size distribution centered around 4–5 nm. Vanadium species were highly dispersed in the samples, as confirmed by the wide angle XRD and Raman spectroscopy. The surface acidity of the materials was determined by the microcalorimetric adsorption of NH₃. Temperature programmed reduction and O₂ chemisorption were used to probe the redox property of the materials. It was found that the mesoporous V–Ce–Ti–O possessed bifunctional characters of acidic and redox properties that catalyzed the oxidation of methanol to dimethoxymethane (DMM). These bifunctional characters were further enhanced by the addition of V₂O₅ and SO₄ ^2? onto V–Ce–Ti–O simultaneously. Such supported catalysts exhibited excellent performance for the selective oxidation of methanol to DMM. Specifically, 72% conversion of methanol with 85% selectivity to DMM was achieved at 423 K over a SO₄ ^2?–V₂O₅/V–Ce–Ti–O catalyst.     

Facile synthesis of hierarchical Co–Mo–O–S porous microspheres for high-performance supercapacitors

Transition metal oxides are considered promising functional materials for energy storage, but their poor conductivity and stability limits their application in energy storage devices. The conductivity and stability of transition metal oxides can be significantly improved by nanostructuring the material, and in this work we report a method for preparing porous Co–Mo–O–S microspheres. As a supercapacitor electrode, Co–Mo–O–S demonstrated a high capacitance of 1134 F g⁻¹ at 1 A g⁻¹ as well as a high rate capability. A hybrid supercapacitor composing Co–Mo–O–S vs reduced graphene oxide delivered a high energy density of 67.6 Wh kg⁻¹, which is much higher than most previously reported results. Therefore, Co–Mo–O–S are expected to be widely used in energy storage devices.     

Emulsion–ion extraction technique for synthesis of hollow bicomponent oxide microspheres

Abstract

H ollow ox ide microspheres in the bicomponent systems Al₂O₃-28 wt-%SiO₂ (AS) ( mullite) , Al₂O₃- 13 wt-%T iO₂ (AT) , and Z rO₂-10 wt-%Y₂O₃ ( Z Y) were prepared by the emulsion-ion extraction technique. Monodisperse microsphere formation was found to depend on the experimental parameters adopted during ion ex traction and the surfactant concentration present in the emulsion system. Powder characteristics were investigated using X-ray diffraction, optical and scanning electron microscopy, and particle size analysis. The gel microspheres in the AS, AT , and ZY systems started crystallising at about 900, 800, and 400 °C respectively. The oxide microspheres were mostly spherical in morphology and the sphericity was retained even after calcination at 1300 °C for 1 h. Formation of hollow microspheres with a single spherical cavity was identified by SEM . All oxide microspheres calcined at 1300 °C for 1 h ex hibited a particle size distribution within the range 5-60 μm, the average size ( d₅₀) varying from 19 to 22 μm. BCT / 537     

On the oxidation behavior of ZrB2–SiC–VC composites

In this study, near-fully dense ZrB₂–SiC–VC (75-20-5 vol%) composite was manufactured through hot pressing at 1850°C under the pressure of 40 MPa for 60 min. Then the oxidation examination of the composite was carried out under different durations and temperatures. The microstructure and phase evolution after hot pressing and oxidation processes were examined by scanning electron microscopy, and X-ray diffractometry. The VC addition led to the formation of ZrC and VSi₂ phases, which assisted the densification of the composite by removing ZrO₂ from the particles’ surface. The oxides of ZrO₂, SiO₂, ZrSiO₄, V₂O₅, and VO₂ formed distinct layers on the sample during the oxidation at 1700°C for 4 h with a parabolic regimen and activation energy of 177.5 kJ/mol.     

Facile synthesis of a Co–B nanoparticle catalyst for efficient hydrogen generation via borohydride hydrolysis

A Co–B nanoparticle catalyst was prepared by a modified polyol method. Borohydride served both as a reducing agent for Co²⁺ and as a boron source, and the solvent, ethylene glycol, served as the surfactant and stabilizer to assemble Co–B clusters into small and uniform particles. The as-prepared Co–B possessed high surface active metal area and highly unsaturated coordinated Co metal, resulting in lower activation energy and higher hydrogen generation rate for hydrolysis of alkaline NaBH₄ solution than the conventional Co–B catalyst synthesized from chemical reduction in water bath.     

Selective oxidation of ethane over hydrothermally synthesized Mo–V–Al–Ti oxide catalyst

Mo–V-based oxide catalysts are known highly active for various hydrocarbon selective oxidations. Particularly those which are monophasic giving XRD diffraction at d=4 Å are extremely active for alkane oxidations. We succeeded to synthesize this unique monophasic material by hydrothermal method and obtained Mo₆V₂Al₁O_x mixed oxide catalysts which showed activities for gas-phase ethane oxidation to ethene and acetic acid. The addition of titanium to the Mo₆V₂Al₁O_x oxide catalyst was found to result in a marked increase of the activity for the ethane selective oxidation, which was due to the morphological change of the catalyst particles and the increase of surface area by the addition of titanium. During the heat-treatment above 550°C under a nitrogen stream, the structural phase of the Mo₆V₂Al₁Ti_0.5O_x catalyst giving the XRD diffraction at d=4 Å transferred to (Mo_0.93V_0.07)₅O₁₄-like phase with drastic decreases of the oxidation activity and the surface area. On the basis of kinetic data and the fact that the lower reaction temperature and the existence of water vapor in the feed facilitated the formation of acetic acid, it is concluded that the breaking of C–H bond of ethane is the rate determining of the oxidation and acetic acid do not form through ethene.     

Effect of pH on the Catalytic Properties of Mo–V–Te–P–O Catalysts for Selective Oxidation of Isobutane

Mo–V–Te–P mixed oxide catalysts, prepared by a dry-up method at various pHs (in the range of about 1.0–9.0), have been tested in the partial oxidation of isobutane. The best catalytic performance was achieved over a catalyst prepared at a pH about 7.0. In this case, high selectivity to methacrolein (37.0%) at an isobutane conversion of 12.7% has been obtained at 380 °C. The surface V⁴⁺/V⁵⁺ ratios of the calcined samples were strongly influenced by the pH in the synthesized solution, which is one of the key factors in the catalytic performance for selective oxidation of isobutane.