Cyclohexanone Selectivity Research Articles

Fabrication of CuCr2O4 spinel nanoparticles: A potential catalyst for the selective oxidation of cycloalkanes via activation of Csp3–H bond

We report here preparation of CuCr2O4 spinel nanoparticle catalyst, mediated by cationic surfactant CTAB in hydrothermal route. XRD revealed the formation of CuCr2O4 spinel phase and TEM showed the particle size of 30–60nm. The catalyst was speculated to be highly active for selective oxidation of cyclohexane to cyclohexanone with H2O2. A cyclohexane conversion of 70% with 85% cyclohexanone selectivity was achieved over this catalyst at 50°C temperature. Moreover, the catalyst did not show any significant activity loss even after 8 reuses and proved its efficacy in the oxidation of other cycloalkanes also.

(nBu4N)4W10O32-catalyzed selective oxygenation of cyclohexane by molecular oxygen under visible light irradiation

The development of mild and efficient process for the selective oxygenation of organic compounds by molecular oxygen (O2) can be one of the key technologies for synthesizing oxygenates. Here, the photo-oxygenation of cyclohexane to cyclohexanol and cyclohexanone over tetrabutylammonium decatungstate (W10O324−) was carried out under visible light irradiation and pure O2 atmosphere. The W10O324− was found to be active to this photo-oxygenation in a pure acetonitrile (MeCN), which can achieve ca. 8.1% cyclohexane conversion with ca. 64.3% selectivity for cyclohexanone under sustained visible light irradiation of 12h. Notably, the above-described photo-catalysis oxygenation was improved to some extent in the presence of some acidic additives such as10M HCl, H2SO4, or H3PO4 aqueous solution and benzenesulfonic acid, providing ca. 12.4–14.3% cyclohexane conversion with ca. 59.7–69.4% cyclohexanone selectivity. Moreover, this acid-promoted effect was further magnified in the case of adding a suitable amount of water, which can lead to enhancing conversion (16.8–20.0%) and improving cyclohexanone selectivity (68.2–78.3%). This acidic aqueous solution-promoted effect was also observed upon the W10O324−-photocatalyzed oxygenation of other substrates like toluene, ethylbenzene and butanone. This is likely due to the acidic aqueous solutions playing important roles in improving photo-redox cycling of W10O324− and preserving its stability, as supported by the UV–vis spectra and cyclic voltammetry measurements.

Facile one-pot approach to the synthesis of spherical mesoporous silica nanoflowers with hierarchical pore structure

Hierarchically structured spherical mesoporous nanoflowers (HSMNF) with well-defined morphology and uniform size were synthesized by a hydrothermal method, in which a mixture of cyclohexane and water was used as the solvent, with cetylpyridinium bromide (CPB) as the template, tetraethyl orthosilicate as the source of inorganic silica, and urea as the hydrolysis additive. The flower size ranged from 200 nm to 500 nm, and the thickness of a “petal” was about 10 nm. We investigated the effects of solvent composition (Vcyclohexane/Vwater), hydrothermal temperature, and molar ratio of Si to CPB on morphology and structure. The presence of cyclohexane was found to be crucial for the nanoflowers to form, and a solvent with high cyclohexane content was beneficial for the formation of smaller and more uniform nanoflowers, whereas low cyclohexane content resulted in the collapse of the nanoflower structure. The optimal ratio of cyclohexane to water was 1:1 by volume. The hydrothermal temperature and molar ratio of Si to CPB strongly affected nanoflower size and structure, as well as petal thickness. The optimal hydrothermal temperature was 120 °C, and the optimal molar ratio of Si to CPB was 4.37. The sample synthesized under optimal conditions exhibited well-defined morphology and uniform flower size. Its BET surface area reached 502 m2/g. The nanoflowers were under 200 nm in diameter, and their average mesopore size was ca. 4 nm, as measured by N2 adsorption–desorption. Using synthesized nanoflowers as the support, we prepared a supported PdAu bimetallic catalyst for the hydrogenation of phenol. This catalyst exhibited high activity (with a conversion rate of up to 90%) and high selectivity for cyclohexanone (up to 92%). This nanoflower's morphology, high surface area, and large pore size may make it a valuable and promising material for applications in the catalysis, adsorption and controlled release of drugs fields.

Aerobic Oxidation of Cyclohexane Effectively Catalyzed by Simply Synthesized Silica-Supported Cobalt Ferrite Magnetic Nanocrystal

Silica-supported magnetic cobalt ferrite complex oxides, CoFe2O4/SiO2, with different loading of 5, 10, 20, and 50% were simply prepared by a sol–gel autocombustion method using colloidal aqueous silica solution as a cheap silica source. The as-prepared samples were well characterized by X-ray diffractometry (XRD), Fourier transform infrared spectrophotometry (FT-IR), transmission electron microscopy (TEM), and N2 physisorption. Metals contents of the samples were also determined by atomic absorption spectrophotometry. Their catalytic performances were evaluated on cyclohexane oxidation using oxygen as oxidant in the absence of solvents and reductants. The supported catalysts have shown high catalytic activities for cyclohexane oxidation. Especially, when 5% loading of CoFe2O4/SiO2 was employed, 4181 turnover number and 95.4% selectivity for cyclohexanone and cyclohexanol were obtained under 1.6 MPa of initial oxygen pressure at 418 K after 6.0 h of reaction. The sample of 50% of CoFe2O4/SiO2 has strong m...

Synthesis, characterization of MCM-41 with high vanadium content in the framework and its catalytic performance on selective oxidation of cyclohexane

V-MCM-41 with high content of vanadium in the framework was synthesized by using direct hydrothermal method under alkaline condition. Tartaric acid is the complexing reagent and cetyltrimethylammonium bromide is the structure-directing agent. The samples were characterized by X-ray fluorescence, X-ray diffraction, high-resolution transmission electron microscopy, N2 adsorption–desorption, Fourier-transform infrared spectroscopy, diffuse reflectance ultraviolet–visible spectroscopy and X-ray photoelectron spectroscopy techniques. The catalytic performance for the selective oxidation of cyclohexane was also examined. The results showed that the vanadium atoms were successfully introduced into the MCM-41 framework and the vanadium content reached up to 8.1wt.%. Moreover, the V-MCM-41 samples possessed regular and stable structure with high specific surface area (692–939m2g−1), large pore diameter (3.6–4.6nm) and large pore volume (0.86–0.95cm3g−1). The samples exhibited excellent catalytic performance of up to 22.57% cyclohexane conversion and 99.53% selectivity for cyclohexanone and cyclohexanol in the cyclohexane oxidation.

Carbon Nanotubes and Activated Carbons Supported Catalysts for Phenol in Situ Hydrogenation: Hydrophobic/Hydrophilic Effect

Carbon nanotube (CNTs) and activated carbon (AC) supported Pd and Ni catalysts were prepared for the (in situ) hydrogenation of phenol to cyclohexanone and cyclohexanol. The hydrophobic/hydrophilic properties of the catalysts were tailored by pretreating the carbonaceous support with HNO3 at various conditions and characterized by X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption (TPD), and transmission electron microscopy (TEM). The catalytic results suggested that Pd and Ni supported on CNTs show significantly higher activity than that supported on ACs. Pretreating the CNTs with HNO3 increases the local hydrophilicity of the active phase (by introducing oxygenated groups), which result in an increase in the cyclohexanone selectivity and strongly decrease the phenol conversion. The first-principles density functional theory calculation suggested that the adsorption/desorption behaviors of phenol, methanol, H2O, and cyclohexanone on the catalysts might be influenced highly by the h...

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.

Selective Hydrogenation of Phenol and Derivatives over Polymer-Functionalized Carbon-Nanofiber-Supported Palladium Using Sodium Formate as the Hydrogen Source.

Selective hydrogenation of phenol to cyclohexanone over a catalyst of polyaniline-functionalized carbon-nanofiber-supported palladium (Pd-PANI/CNF) with sodium formate as the hydrogen source has been studied. Phenol conversion exceeding 99 % was achieved with a cyclohexanone selectivity of >99 % in aqueous media. In an extension to Pd-PANI/CNF, polymers such as polypyrrole (PPY), poly(4-vinylpyridine) (PVP), and poly(1-vinylimidazole) (PVI) were further applied to a catalyst of Pd-polymer/CNF for selective phenol hydrogenation. All of the Pd-polymer/CNF catalysts showed excellent to good performance toward selective phenol hydrogenation. However, Pd-PANI/CNF was considerably more active and selective to afford the desired cyclohexanone than Pd-PPY/CNF, Pd-PVP/CNF, and Pd-PVI/CNF. Moreover, a series of phenol-derived compounds were selectively hydrogenated in high yields under the investigated aqueous conditions. The research highlights an environmentally benign and effective process for the selective reduction of phenol derivatives with sodium formate as an alternative hydrogen source.

Dehydrogenation of cyclohexanol over Cu/Al2O3 catalysts prepared with different precipitating agents

Dehydrogenation of cyclohexanol over Cu/Al2O3 catalysts (molar Cu:Al=1:1) prepared by reduction of mixed oxide precursors synthesized using different precipitating agents viz. potassium carbonate, tetraalkyl ammonium hydroxides (TAAOHs) and urea was investigated. In order to assess the efficacy of TAAOH further, the chain length of tetraalkyl ammonium cations was also varied and the resulted catalysts were evaluated for their catalytic performance. The catalysts were characterized by powder X-ray diffraction, low temperature nitrogen adsorption, temperature programmed desorption of ammonia and UV–visible diffuse reflectance spectroscopy. The dependence of the catalyst performance on the precipitating agent employed during its synthesis has been clearly demonstrated. The use of TAAOH as precipitating agent led to the formation of a catalyst with better catalytic activity than those prepared using potassium carbonate and urea. Further improvement in the catalytic performance was observed when TAAOH with longer alkyl chain ammonium cation was used. The optimum catalyst prepared by reduction of mixed oxide precursor synthesized using tetrapropyl ammonium hydroxide as precipitating agent, showed highest cyclohexanol conversion (81.5%) and cyclohexanone selectivity (79.6%) at 250°C on account of higher Cu+/Cu0 ratio, well dispersed copper, higher surface area and lower total acidity with higher contribution of sites with moderate strength.

Immobilization of highly active Pd nano-catalysts on functionalized mesoporous silica supports using mercapto groups as anchoring sites and their catalytic performance for phenol hydrogenation

Highly active and highly dispersed Pd-loaded nano-catalysts using mercapto group (–SH) functionalized mesoporous silica supports, namely, Pd-SH-MCM-41 and Pd-SH-SBA-15, were prepared using an impregnation-reduction approach. The surface –SH groups are believed to facilitate the high distribution and immobilization of the Pd nanoparticles within the silica supports through an anchoring interaction. The catalysts featured long-range ordered structures, uniform pore size, high surface area, and highly dispersed Pd nanoparticles as characterized by X-ray diffraction, N 2 adsorption-desorption, and transmission electron microscopy. The catalysts showed activity five times higher than that of commercial Pd/C catalyst and three times higher than those of Pd/MCM-41 and Pd/SBA-15 catalysts. Within 1 h of reaction at 80 °C and 1.0 MPa, the conversion of phenol attained was greater than 99%, and the selectivity for cyclohexanone was 98%. Highly dispersed Pd nanoparticle catalyst on –SH-functionalized mesoporous silica (Pd-SH-MCM-41) was prepared by anchoring interaction between –SH groups and Pd cations. This catalyst showed very high catalytic activity (>99%) for the hydrogenation of phenol.

Uncatalyzed Oxidation of Cyclohexane in the Microchannels

The oxidation of cyclohexane in the microchannels not only improves the safety of the reaction, but also the performance of the oxidation reaction. Different gas-liquid micro mixers were used for the mixing of gas and liquid before entering into microchannels, and SIMM-V2 performed best of all. Excellent slug/plug flow can be formed in the microchannels after mixing in the gas-liquid micro mixer when the molar ratio of oxygen to cyclohexane is less than 0.5:1. The conversion of cyclohexane increased as the residence time increased, but the selectivity of cyclohexanol and cyclohexanone increased first and then decreased. At the reaction temperature of 200 °C, with the flow rate of the solvent isopropanol being 1 mL/min and the molar ratio of oxygen to cyclohexane being 0.15:1, both the conversion of cyclohexane and selectivity of cyclohexanol and cyclohexanone increased with the increase of pressure. The conversion of cyclohexane and selectivity of cyclohexanol and cyclohexanone reached 10.10% and 66.93% respectively at the pressure of 8 MPa. It is indicated that the new process by use of uncatalyzed cyclohexane oxidation in the microchannels will have very attractive prospects in the improvement of the safety, intensification of the gas-liquid mass transfer and obtaining good reactive performance. Therefore, the technology shows good potential in industrial applications.

Selective decomposition of cyclohexyl hydroperoxide by copper ion-containing quaternary ammonium salts in alkali-free medium

Abstract A novel catalytic system composed of quaternary ammonium salts and copper (II) chloride was prepared. The catalyst showed high conversion and selectivity in the decomposition of cyclohexyl hydroperoxide to cyclohexanol and cyclohexanone (K/A oil) at room temperature in alkali-free medium. 93% conversion with 96% selectivity for cyclohexanone and cyclohexanol could be obtained.

Zeolite-Y entrapped Ru(III) and Fe(III) complexes as heterogeneous catalysts for catalytic oxidation of cyclohexane reaction

Catalysis is probably one of the greatest contributions of chemistry to both economic growth and environmental protection. Herein we report the catalytic behavior of zeolite-Y entrapped Ru(III) and Fe(III) complexes with general formulae [M(VTCH)2·2H2O]+-Y and [M(VFCH)2·2H2O]+-Y [where, VTCH=vanillin thiophene-2-carboxylic hydrazone and VFCH=vanillin furoic-2-carboxylic hydrazone] over the oxidation of cyclohexane forming cyclohexanone and cyclohexanol. The samples were corroborated by various physico-chemical techniques. These zeolite-Y based complexes are stable and recyclable under current reaction conditions. Amongst them, [Ru(VTCH)2⋅2H2O]+-Y showed higher catalytic activity (41.1%) with cyclohexanone (84.6%) selectivity.

Catalytic Dehydrogenation Reaction Activity of Cyclohexanol over Cu<sub>2</sub>O/Mg(OH)<sub>2</sub> Catalysts

A series of supported Cu2O catalysts on Mg(OH)2 or γ-Al2O3 were prepared by coprecipitation-chemical reduction combined with impregnation using Cu(NO3)2 as precursor salt and hydrazine hydrate as the reducing agent. The crystal phase characteristics and specific suface area of the samples have been characterized by means of X-ray powder diffraction (XRD) and BET method. Catalytic dehydrogenation reaction activity of cyclohexanol over the catalysts was investigated. Results showed Cu2O is the main active component over the supported catalysts. Cu2O Grain has good dispersion in nanoscale. Acid or alkali type of the support has great influence on cyclohexanol dehydrogenation activity of supported Cu2O catalysts. There have cyclohaxene and cyclohexanone products over the supported catalysts. The reaction activity of Cu2O/ Mg(OH)2 catalysts changed with hydrazine hydrate volume. Cyclohexanol conversion and cyclohexanone selectivity can reach to 97.2% and 71.2%.

A facile one-pot synthesis of hierarchically porous Cu(I)-ZSM-5 for radicals-involved oxidation of cyclohexane

An extraordinarily high catalytic performance of up to 28% cyclohexane conversion and above 93% selectivity for cyclohexanone and cyclohexanol in the cyclohexane oxidation has been achieved under mild conditions by using copper-doped hierarchically micro/mesoporous zeolite ZSM-5, which has been fabricated by a facile one-pot hydrothermal synthetic process at a relatively low hydrolysis temperature. The excellent catalytic activity was ascribed to the highly dispersed framework copper ions (Cu+/Cu2+) as catalytic active sites and the hierarchically porous structure to provide the fast diffusion pathway for reactant/product molecules. The presence of the framework Cu(I) was proposed to promote the decomposition of H2O2 and the formation of radicals HO, and thus accelerate the selective oxidation of cyclohexane. More importantly, the synthesized catalyst showed excellent recyclable properties, demonstrating the high catalytic stability and future application prospect of such hierarchical heterogeneous catalysts in chemical industry.

Preparation of copper (II) ion-containing bisimidazolium ionic liquid bridged periodic mesoporous organosilica and the catalytic decomposition of cyclohexyl hydroperoxide

A novel bisimidazolium ionic liquid bridged periodic mesoporous organosilica was prepared. Bisimidazolium ionic liquid was incorporated into the framework of mesoporous materials and copper (II) chloride can be easily introduced to the framework via the formation of CuCl 4 2 − complex. This copper (II) ion-containing bisimidazolium ionic liquid bridged material showed high activity and stability in the decomposition of cyclohexyl hydroperoxide. Ninety-nine percent conversion and 84% selectivity for cyclohexanone and cyclohexanol (K/A oil) could be obtained. ► Cu 2 + -containing bisimidazolium ionic liquid bridged PMO was prepared. ► The catalyst showed high activity in the decomposition of cyclohexyl hydroperoxide. ► The catalyst showed prominent stability.

External field-assisted solution synthesis and selectively catalytic properties of amorphous iron nanoplatelets

This work describes an easy and flexible approach for the synthesis of 2D nanostructures by external composite field-induced self-assembly. Amorphous iron nanoplatelets with a large aspect ratio were prepared by reducing a concentrated FeSO4 solution with NaBH4 without any templates or surfactants under a magnetic field and a shear field, and characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD). Based on the morphological dependence of the resultant iron nanostructures on the kinetic parameters such as reactant concentration, reaction temperature, external fields as well as reaction time, etc., a novel conceivable formation mechanism of the iron nanoplatelets was substantiated to be a self-assembly of concentrated iron nuclei induced by the synergistic effect of both a magnetic field and a shear field. Due to the amorphous nature and shape anisotropy, the as-synthesized iron nanoplatelets exhibit quite different magnetic properties with an enhanced coercivity of >220 Oe from isotropic iron nanoparticles. In the oxidation of cyclohexane with hydrogen peroxide as a “green” oxidant, the as-obtained amorphous iron nanoplatelets show a conversion more than 84% and a complete selectivity for cyclohexanol and cyclohexanone due to the unique structure. Moreover, their catalytic performances are strongly influenced by their morphology, and the iron atoms located on the faces tend to catalyze the formation of cyclohexanol while those on the sides tend to catalyze the formation of cyclohexanone. The external composite field-induced solution synthesis reported here can be readily explored for fabricating other 2D magnetic nanoplatelets, and the resulting iron nanoplatelets are promising for a number of applications such as high efficient selective catalysis, energy, environment fields and so forth.

Room temperature selective oxidation of cyclohexane over Cu-nanoclusters supported on nanocrystalline Cr2O3

Cu-nanoclustures supported on nanocrystalline Cr2O3 were prepared by a hydrothermal synthesis method in the presence of surfactant, cetyltrimethylammonium bromide (CTAB). It was found that the catalyst is highly active for the selective oxidation of cyclohexane with H2O2 at room temperature. The catalyst was characterized by XRD, ICP-AES, XPS, TPR, BET-surface area, SEM, TEM and EXAFS. The effect of Cu loading and the influence of reaction parameters, such as the substrate to oxidant molar ratio and reaction time, were investigated in detail. The investigation revealed that the size of copper plays a crucial role towards the activity by favoring the oxidation of cyclohexane. The reusability of the catalyst was tested by conducting repeat experiments with the same catalyst, where it was found that the catalyst displays no changes in its activity and selectivity even after 4 reuses. The cyclohexane conversion of 86% with a cyclohexanone selectivity of 85%, and an overall C6 selectivity (cyclohexanol and cyclohexanone) of 100% was achieved after 3 h of reaction at room temperature, over 4.3 wt% Cu loaded on nanocrystalline Cr2O3.

Metal chlorides-catalyzed selective oxidation of cyclohexane by molecular oxygen under visible light irradiation

The development of mild and efficient process for the selective oxidation of organic compounds with molecular oxygen can be one of the key technologies for synthesizing oxygenates. Here, a visible light-driven metal chloride to catalyze the selective oxidation of cyclohexane was carried out at ambient temperature under a pure O2 atmosphere. Among the metal salts examined, only a few metal chlorides, with easily changeable valence, such as CuCl2·2H2O, VOCl3, and FeCl3·6H2O, were found to be active to this photo-oxidation reaction in acetonitrile or acetone, providing cyclohexanol, cyclohexanone, chlorocyclohexane, and cyclohexene as main products. This is likely because the weak coordination of these metal chlorides with solvent molecules plays key roles in absorbing visible light and realizing photoredox cycle, as supported by UV–Vis spectrum and cyclic voltammetry measurements. Among these active metal chlorides, CuCl2·2H2O showed a higher conversion and better selectivity for cyclohexanol and cyclohexanone (the oxygenated products) than the other two metal chlorides, and its activity and selectivity for chlorocyclohexane were significantly improved in the case of adding concentrated HCl, because HCl promotes the photocatalytic cycling, as supported by UV–Vis spectra. Notably, a high turnover frequency (TOF, 7.4h−1) and an excellent selectivity for the oxygenated products (93%) were achieved upon a low concentration of CuCl2·2H2O (0.002molL−1), 0.1ml of concentrated HCl and 2atm of O2 pressure. Based on these findings, a free radical mechanism for the present photocatalysis system was proposed.

Experimental Study on Cyclohexane by Catalytic Oxidation Using H<sub>2</sub>O<sub>2</sub>/Ferrous Sulfate

Catalytic oxidation of cyclohexane to cyclohexanone and cyclohexanol using hydrogen peroxide over ferrous sulfate catalyst at atmospheric condition was studied. Effect of the solvent volume, catalyst amount, hydrogen peroxide volume, reaction temperature, reaction time on reaction was investigated. Results showed that using 10 mL of acetone, 0.02 g of a ferrous sulfate and 0.5 mL of hydrogen peroxide at thereaction temperature of 80 °C for 8 h, the conversion of cyclohexane was 35.35%, the total selectivity of cyclohexanone and cyclohexanol was 94.06%.