Partial Oxidation Of Cyclohexane Research Articles

Modular calcination strategy to construct defect-rich nitrogen-doped Nb2O5 for boosting photocatalytic oxidation of cyclohexane to cyclohexanone in solvent-free conditions

The partial oxidation of cyclohexane (CHA) with oxygen to cyclohexanone (CHA-one) is one of the most transformation in the chemical industry in view that CHA-one is an irreplaceable raw material in the production of nylon. Herein, hydrogen, vacuum and air modules combined with ammonia module, respectively, were used to construct defect-rich nitrogen-doped Nb2O5. And, the calcination order and temperature were also considered to establish a modular calcination strategy. A series of modified N-doped Nb2O5 were prepared by the proposed strategy, which were used to catalyze the photo-oxidation of CHA in solvent-free and room temperature conditions. Among these modified N-doped Nb2O5 samples, the HN-Nb2O5 possessed abundant chemical defects of oxygen vacancies and Nb4+, and achieved the best photocatalytic performance. Surprisingly, HN-Nb2O5 achieved an amount of 130.35 μmol for CHA-one, which was approximately 2.2 and 26 times that of the pure Nb2O5 and commercial Nb2O5, respectively, with up to 96.68% selectivity to CHA-one. The outstanding photocatalytic performance of the HN-Nb2O5 can be ascribed to the presence of chemical defect-rich and the NOx species, enhanced light absorption and effective electron-hole separation. DFT calculations explained the promotion of the chemical defects and N doping on Nb2O5 photocatalytic activity in terms of the band electron and band-gap level. The results of EPR analysis and scavenger tests found that e− is the main active species resulted in photocatalytic activity, while O2− is the dominant active species for producing CHA-one in the photo-oxidation of CHA. The present work developed an efficient strategy to construct the defect-rich N-doped metal oxide for the improved photocatalytic oxidation of hydrocarbon.

Simple synthesis of WO3-Au composite and their improved photothermal synergistic catalytic performance for cyclohexane oxidation

Partial oxidation of cyclohexane (CHA) to KA oil (cyclohexanone (-one) and cyclohexanol (-ol)) with dry air is one of the most important industrial process. Despite great efforts have made in developing new catalysts, industrial processes are still limited by low conversion and selectivity with harsh condition. Here we report a significantly improved cyclohexane conversion and KA oil selectivity under solar light irradiation by anew photothermal synergistic catalyst, which was prepared by loading Au nanoparticles (Au NPs) onto WO3 nanosheets (WO3 NSs) with simple ultrasonic method. A high conversion of 9.0% and a high selectivity of 99.0% are acquired by WO3 nanosheets-Au nanoparticles (WO3-Au) composite under dry air, which are much higher than the simple sum of photocatalysis and thermal catalysis. The significantly improved catalytic properties of cyclohexane oxidation by the WO3-Au composite are mainly attributed to the improved light absorption, the effective charge separation and the synergistic effect of photocatalysis and thermal catalysis. The photothermal synergy to improve catalytic activity may be widely used in green industrial catalytic processes.

C-doped Cr2O3/NaY composite membrane supported on stainless steel mesh with enhanced photocatalytic activity for cyclohexane oxidation

In this study, a C-doped Cr2O3/NaY composite membrane supported on stainless steel mesh with layer-by-layer structure was successfully synthesized and used in the partial oxidation of cyclohexane. In the composite membrane, NaY zeolite membrane acted as absorbent and the C-doped Cr2O3 behaved as photocatalyst, which was successfully prepared using a chromium-containing MOF as precursor. The supported composite membrane was characterized by a series of analysis techniques. Comparing with the stainless steel mesh-supported C-doped Cr2O3 membrane, the supported C-doped Cr2O3/NaY composite membrane exhibited superior visible-light-driven photocatalytic performance for cyclohexane oxidation. This is due to its layer-by-layer structure and NaY membrane with high surface areas and polarity which can preferentially adsorb KA oil products, avoiding their overoxidation.

Metal Azolate/Carboxylate Frameworks as Catalysts in Oxidative and C-C Coupling Reactions.

The five metal azolate/carboxylate (MAC) compounds [Cd(dmpzc)(DMF)(H2O)] (Cd-dmpzc), [Pd(H2dmpzc)2Cl2] (Pd-dmpzc), [Cu(Hdmpzc)2] (Cu-dmpzc), [Zn4O(dmpzc)3]·Solv (Zn-dmpzc·S), and [Co4O(dmpzc)3]·Solv (Co-dmpzc·S) were isolated by coupling 3,5-dimethyl-1H-pyrazol-4-carboxylic acid (H2dmpzc) to cadmium(II), palladium(II), copper(II), zinc(II), and cobalt(II) salts. While Cd-dmpzc and Pd-dmpzc had never been prepared in the past, for Cu-dmpzc, Zn-dmpzc·S, and Co-dmpzc·S we optimized alternative synthetic paths that, in the case of the copper(II) and cobalt(II) derivatives, are faster and grant higher yields than the previously reported ones. The crystal structure details were determined ab initio (Cd-dmpzc and Pd-dmpzc) or refined (Cu-dmpzc, Zn-dmpzc·S, and Co-dmpzc·S) by means of powder X-ray diffraction (PXRD). While Cd-dmpzc is a nonporous 3D MAC framework, Pd-dmpzc shows a 3D hybrid coordination/hydrogen-bonded network, in which Pd(H2dmpzc)2Cl2 monomers are present. The thermal behavior of the five MAC compounds was investigated by coupling thermal analysis to variable-temperature PXRD. Their catalytic activity was assessed in oxidative and C-C coupling reactions, with the copper(II) and cadmium(II) derivatives being the first nonporous MAC frameworks to be tested as catalysts. Cu-dmpzc is the most active catalyst in the partial oxidation of cyclohexane by tert-butyl hydroperoxide in acetonitrile (yields up to 12% after 9 h) and is remarkably active in the solvent-free microwave-assisted oxidation of 1-phenylethanol to acetophenone (yields up to 99% at 120 °C in only 0.5 h). On the other hand, activated Zn-dmpzc·S (Zn-dmpzc) is the most active catalyst in the Henry C-C coupling reaction of aromatic aldehydes with nitroethane, showing appreciable diastereoselectivity toward the syn-nitroalkanol isomer (syn:anti selectivity up to 79:21).

Selective liquid phase oxidation of cyclohexane over Pt/CeO2-ZrO2-SnO2/SiO2 catalysts with molecular oxygen

Partial oxidation of cyclohexane into cyclohexanone and cyclohexanol (KA-oil) is an industrially significant reaction for producing precursors for the synthesis of ɛ-caprolactam and adipic acid, which are the building blocks of nylon. However, to date, the cyclohexane conversion ratio has usually been limited to less than 6% to prevent further oxidation of the cyclohexanol and cyclohexanone targets. In this study, we report that Pt/CeO2-ZrO2-SnO2/SiO2, in which CeO2-ZrO2-SnO2 provide reactive oxygen molecules from inside the bulk, can act as efficient catalysts. Optimization of the catalyst composition and reaction conditions provided a cyclohexane conversion ratio of 24.1% and a total selectivity for cyclohexanol and cyclohexanone of 83.4% at 130 °C in 0.5 MPa (4.9 atm) air for 7 h over a 5wt%Pt/16wt%Ce0.68Zr0.17Sn0.15O2.0/SiO2 catalyst. This catalyst has significant advantages over conventional catalysts because the reaction proceeds at a lower pressure, and there is no need for toxic radical initiators or free-radical scavengers.

Highly selective oxidation of cyclohexane to cyclohexanone using VPO catalysts in a high pressure batch reactor

Vanadyl phosphorous oxide catalysts were synthesized in an organic medium with different molar ratios of P/V and used for partial oxidation of cyclohexane. The catalysts were characterized by BET, XRD, XRF, and SEM measurements. The catalytic activity for the partial oxidation of cyclohexane to cyclohexanone was investigated in a high pressure batch reactor by use of hydrogen peroxide as oxidant. Effects of molar P/V ratio, temperature, and the ratio of the oxidant, cyclohexane, and the catalyst on the selectivity of cyclohexanone were investigated.

Gas-phase Photocatalytic Partial Oxidation of Cyclohexane to Cyclohexanol and Cyclohexanone on Au/TiO2 Photocatalysts

AbstractThe heterogeneous photocatalytic partial oxidation of cyclohexane in gas-phase as an alternative green process for fine chemicals synthesis was successfully achieved on Au/TiO

Binuclear cobalt complex with Schiff base ligand: Synthesis, characterization and catalytic properties in partial oxidation of cyclohexane

A new binuclear cobalt complex with Schiff base ligand and amino acid was synthesized and characterized using XRD, elemental analysis, IR spectroscopy, XPS and electrochemical measurements. The presence of cobalt in the oxidation state 3+ in this complex was proved. The catalytic activity of this complex was investigated in the reaction of partial cyclohexane oxidation with air, and high activity and selectivity for cyclohexanol and cyclohexanone formation were demonstrated. The possibility of complex reuse in cyclohexane oxidation was studied and it was shown that the activity slightly decreases in a second oxidation cycle along with changes in main product distribution due to partial transfer of Co3+ to Co2+.

A catalytic reactor for the trapping of free radicals from gas phase oxidation reactions

A catalytic reactor for the trapping of free radicals originating from gas phase catalytic reactions is described and discussed. Radical trapping and identification were initially carried out using a known radical generator such as dicumyl peroxide. The trapping of radicals was further demonstrated by investigating genuine radical oxidation processes, e.g., benzaldehyde oxidation over manganese and cobalt salts. The efficiency of the reactor was finally proven by the partial oxidation of cyclohexane over MoO(3), Cr(2)O(3), and WO(3), which allowed the identification of all the radical intermediates responsible for the formation of the products cyclohexanol and cyclohexanone. Assignment of the trapped radicals was carried out using spin trapping technique and X-band electron paramagnetic resonance spectroscopy.

Temperature dependence of catalytic cyclohexane partial oxidation in a polytetrafluoroethylene reactor

Polymer-supported Co(II) catalyst was prepared and its activity and selectivity in the partial oxidation of cyclohexane was determined at several temperatures in a polytetrafluoroethylene reactor (PTFE). The catalyst was characterized by means of SEM-EDX, FTIR, diffuse reflectance UV-Vis, N2 sorption, and mecury porosimetry. Activation energies were determined under steady state conditions for the net production of cyclohexanone and cyclohexanol and for cyclohexane and oxygen net consumption. Some activation energies were lower than the ones reported for the uncatalyzed process, indicating that the catalyst played an important role in the initiation of the free-radical reaction.

Experimentally observable transitions between dynamical states in complex reaction systems

Identification of trends and their correspondence with dynamical state transitions are briefly discussed on several reaction network models. The influence of different threshold values on the trend analysis and dynamical state analysis results is examined. Both methods are applied here to the results of the numerical simulation. For this purpose the models of three reaction systems are used: simple model of consecutive, first order, equilibrium reactions, partial oxidation of cyclohexane, and model of the oscillatory reaction Bray Liebhafsky. Detailed kinetic analysis confirmed that transient dynamical states may be identified through the symbolic representation of the sequence of trend episodes in experimentally obtainable time series. Stoichiometric Network Analysis of possible dynamical states was used to identify reaction pathways responsible for the sequences of trend episodes. Some technical problems were also addressed, connected with selection of the threshold value and dynamical state notion.

The Partial Oxidation of Cyclohexane in Supercritical Water

Water is an optimal solvent, reaction partner, or catalyst. Many organic substances do not react or only unsufficiently with or within water at lower temperatures. The behavior changes dramatically when temperature is increased. Near the critical point of water the solubility of water rises rapidly. Cyclohexane can be transformed into cyclohexanol, cyclohexanone, and cyclohexene in supercritical water.

The Influence of Solvents on the Partial Oxidation of Cyclohexane

The Influence of Solvents on the Partial Oxidation of Cyclohexane

The Influence of Solvents on the Partial Oxidation of Cyclohexane

This publication describes the kinetics of the one-step liquid-phase oxidation of cyclohexane to cyclohexanone and cyclohexanol in solutions. Effects of the solvents were examined on the selectivity/conversion relation with regard to the intermediates cyclohexanol and cyclohexanone and their ratio in the reaction mixture. Measurements were carried out in a semibatch reactor at constant temperature (165 °C), and pressure (20 bar) without adding any catalysts. The experimental results can be modeled using a simplified reaction-network. Two models, specific- and unspecific-solvation, were employed to describe the influence of solvents on the different pathways of the developed oxidation network. The specific solvation model is based on the equilibrium between associated and free intermediates. Unspecific influence of the solvents on the reaction-rate can be explained by modeling the reaction-rate constants on the basis of the Kirkwood equation using the dielectric constant of the reaction mixture.

Partial oxidation of cyclohexane with reductively activated dioxygen on SmCl3supported on graphite during H2–O2fuel cell reactions

The oxidation of cyclohexane to cyclohexanol (CyOH) and cyclohexanone (CyO) on SmCl3 supported on graphite (SmCl3/Gr) utilizing an H2–O2 fuel cell system has been studied by means of kinetic and electrochemical techniques. O2 is reductively activated on SmCl3/Gr with e– and H+ which are supplied from the anode. The kinetic and electrochemical results have suggested that the current is determined by the electrochemical reduction of O2, but the oxygenate formation depends strongly on the stationary concentration of active oxygen (O*) generated on SmCl3/Gr. The optimum rate of formation of the products was obtained at a cathode potential of –0.24 V (vs. Ag|AgCl). The active site on SmCl3/Gr was suggested to be a Sm3+ coordinated with surface functional groups on the graphite. The reaction between the O* and cyclohexane proceeds through a non-electrochemical reaction and produces CyOH and CyO in parallel. The selectivity of the products on SmCl3/Gr did not change appreciably under different cathode potentials and O2 pressures. However, the selectivity varied widely for the oxidation on FeCl3/Gr. These observations suggest different O* species between SmCl3/Gr and FeCl3/Gr.

The Partial Oxidations of Cyclohexane and Benzene on the FeCl3 ‐ Embedded Cathode during the O 2 ‐ H 2 Fuel Cell Reactions

Activation and partial oxidations of cyclohexane and benzene occur at ambient temperatures on cathodes containing various metal chlorides during fuel cell reactions. Among the metal chlorides embedded in graphite cathodes, was the most effective for enhancing the partial oxidation of cyclohexane into cyclohexanol and cyclohexanone. This cathode was also effective for the hydroxylation of benzene to phenol. The effects of various kinetic factors on the rate of oxidations of cyclohexane and benzene have been examined. The kinetic results have been explained in terms of the reaction mechanism proposed. It is suggested that the activation and partial oxidation of cyclohexane and aromatics are initiated by an active oxygen, O*, generated on the iron cations at the cathode due to the reduction of dioxygen during the fuel cell reactions. Experiments using as the oxidant have indicated that the cannot be a precursor of the active oxygen O*. The product distribution observed in the oxidation of toluene implies that the O* has a character more electrophilic than OH radicals.