Liquid-phase Oxidation Of Cyclohexane Research Articles

Ni-Amino Acid–CaAl-Layered Double Hydroxide Composites: Construction, Characterization and Catalytic Properties in Oxidative Transformations

Host–guest composite materials were prepared applying the anionic forms of Ni(II)-amino acid (l-histidine, l-cysteine, and l-tyrosine) as the guests and CaAl-layered double hydroxide (CaAl-LDH) as the host. The syntheses were performed either by introducing the amino acid anions first and then constructing the metal ion–amino acid complexes or intercalating the pre-prepared complexes in anionic forms. The pristine as well as the composite LDH samples were structurally characterized by X-ray diffractometry, mid IR spectroscopy and scanning electron microscopy. The structural features of the interlayer complexes were studied by UV–Vis, inductively coupled plasma optical emission, mid and far IR and X-ray absorption spectroscopies as well as energy-dispersed X-ray analysis. On the basis of the acquired data, structural models were constructed. The composites were applied as catalysts in the liquid-phase oxidation of cyclohexene applying peracetic acid and the in situ formed iodosyl benzene as oxidants. Using peracetic acid afforded epoxide, while applying iodosyl benzene provided cis diol as the major or exclusive oxidation product. The catalysts displayed good recycling properties.

Catalytic Performance of MgO-Supported Co Catalyst for the Liquid Phase Oxidation of Cyclohexane with Molecular Oxygen

A highly-efficient and stable MgO-supported Co (Co/MgO) catalyst was developed for the oxidation of cyclohexane with oxygen. The effects of the Co loading and support on the catalytic activity of the supported Co3O4 catalyst were investigated. The results show that the Co supported on MgO presented excellent activity and stability. When the Co/MgO catalyst with the Co content of 0.2 wt% (0.2%Co/MgO) was used, 12.5% cyclohexane conversion and 74.7% selectivity to cyclohexanone and cyclohexanol (KA oil) were achieved under the reaction conditions of 0.5 MPa O2 and 140 °C for 4 h. After being repeatedly used 10 times, its catalytic activity was hardly changed. Further research showed that the high catalytic performance of the 0.2%Co/MgO catalyst is attributed to its high oxygen-absorbing ability and the high ratio between the amount of weak and medium base sites with the help of the synergistic interaction between Co and MgO.

Promoting effect of ionic liquids in liquid-phase oxidation of cyclohexane with a mixture of О2 and Н2

The low efficiency of H2 usage in the oxidation of organics with O2–H2 gas mixture is still a challenging problem. Here, a significant improvement of cyclohexane oxidation has been achieved by introduction of some ionic liquids into Pt/C–H3PMo12O40–CH3CN catalytic system. Even small amounts of BMImBr, Bu4NBr or Bu4NHSO4 inhibited H2O formation, enhanced efficiency of H2 consumption from 2 to 18–25%, and provided extraordinary high selectivity (92–98%) for the conversion of cyclohexane to cyclohexanol. The positive effect of the ionic liquids was explained by stabilization of an active peroxide species and inhibition of secondary oxidation of cyclohexanol.

Probing the Catalytic Activity of Tin-Platinum Decorated Graphene; Liquid Phase Oxidation of Cyclohexane

Pt-Sn supported on reduced graphene oxide (Pt-Sn/rGO) was synthesized and characterized by SEM, EDX, and XRD. The catalytic activity of Pt-Sn/rGO was tested for the solvent free liquid phase oxidation of cyclohexane to a mixture of cyclohexanol and cyclohexanone, also called KA oil, under mild reaction conditions. The products were analyzed gravimetrically, by UV spectrophotometer, and GC equipped with FID. The catalyst was found to be fairly active as well as selective for the desired products. The experimental data was analyzed by Freundlich, Temkin, and Langmuir adsorption isotherms. The L-H model was found to give a better fit of the data. The catalyst was fully recyclable and truly heterogeneous.

Tuning of the reaction parameters to optimize allylic oxidation of cyclohexene catalyzed by zeolite-Y entrapped transition metal complexes

The synthetic protocols for entrapment of transition metal complexes reported here are to expand the diversity in catalysis made possible by the ability of microporous solid to select reactants, transition states, and products based on their molecular size. Herein, we report a synthetic route for the entrapment of transition metal complexes within the nanopores of zeolite-Y. The complexes of transition metals [M=Fe(II), VO(IV)] with Schiff base ligands that are synthesized by simple condensation of 2-hydroxyacetophenone and/or 2-hydroxy-5-chloroacetophenone with ethylenediamine have been entrapped within nanopores of zeolite-Y by flexible ligand method. These materials have been characterized by various physicochemical and spectroscopic techniques such as ICP-OES, FT-IR, 1H and 13C NMR, elemental analyzes, and UV–vis electronic spectral studies, BET, TGA, scanning electron micrographs (SEMs), X-ray diffraction patterns (XRD), conductivity, magnetic susceptibilities as well as AAS. These synthesized catalysts have been utilized as heterogeneous catalysts for liquid phase oxidation of cyclohexene. The reaction parameters have been tuned to optimize higher cyclohexene conversion (%) along with higher selectivity towards the formation of corresponding allylic products. These catalysts were recovered and reused for three times without remarkable loss of activity. Moreover, the intermediate species involved during the catalytic oxidation reaction was synthesized and identified by FTIR and UV–vis spectroscopy.

Solvent-free oxidation of cyclohexane over covalently anchored transition-metal salicylaldimine complexes to α-zirconium phosphate using tert-butylhydroperoxide

Heterogeneous catalysts were prepared by covalent bonding of transition-metal salicylaldimine complex to α-zirconium phosphate, abbreviated as {α-ZrP.M(salicylaldimine) where M=Co, Mn and Cu}. The resulting compounds were characterized by BET surface area, TGA analysis, X-ray diffraction, Scanning electron micrograph, energy dispersive X-ray analysis, Fourier transform infrared and Atomic absorption spectroscopy. The catalytic activity of α-ZrP.M(salicylaldimine) was studied for the liquid phase oxidation of cyclohexane using tert-butylhydroperoxide as an oxidant under solvent free condition. In the oxidation reaction, cyclohexane was oxidized to cyclohexanol, cyclohexanone and some unidentified products. It was found that the reactivity of α-ZrP.M(salicylaldimine) catalyst for the oxidation reaction decreased in the order α-ZrP.Co(salicylaldimine)>α-ZrP.Mn(salicylaldimine)>α-ZrP.Cu(salicylaldimine). A maximum conversion of cyclohexane (14.18%) and selectivity of cyclohexanol (4.99%), cyclohexanone (87.34%) and some other products (7.67%) was observed for catalyst, α-ZrP.Co(salicylaldimine) after 6h at 353K. The catalyst, α-ZrP.Co(salicylaldimine) was reused for four cycles without significant loss of catalytic activity.

Synthesis and characterization of Au nanocatalyst on modifed bentonite and silica and their applications for solvent free oxidation of cyclohexene with molecular oxygen

In the present work, the selective liquid phase oxidation of cyclohexene mainly to 2-cyclohexe-1-one has been investigated over gold nanoparticles (GNPs) with molecular oxygen in a solvent-free condition. Gold nanoparticles were synthesised on two modified supports of silica and bentonite. In this respect the surface of silica and bentonite was modified with organic ligands consist of thiol and thioester groups. The catalysts were characterized by TEM, XPS, N2 adsorption/desorption, FT-IR, and CHNS techniques. TEM images show that the gold nanoparticles over modified bentonite and silica have diameters in the range 0f 50 and less than 10nm, respectively. The results show that the catalytic activity of gold nanoparticles over modified silica, SiO2-pA-Acrylate-Thioamide-Au (0), is much better than the gold nanoparticles immobilized on the modified bentonite, MEDPT@CP-bentonite-Au (0). The catalytic activity over SiO2-pA-Acrylate-Thioamide-Au (0) recycled catalyst remained at a satisfactory state after at least 4 cycles. Activity tests were carried out in an autoclave under solvent-free conditions. In order to obtain maximum conversion, the reaction parameters such as reaction temperature and time were optimized. Under optimized conditions, a maximum of 92% conversion and 97% selectivity was achieved with the SiO2-pA-Acrylate-Thioamide-Au (0) catalyst.

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.

Amino acids and their derivatives in catalytic cyclohexane oxidation

Homogeneous catalytic oxidation of cyclohexane can be improved by using additives to industrial catalysts that are based on variable valence metals. Recent studies have been much focused on enzymatic catalysis with protein-based enzymes that consist of amino acids of various structures. We assume that the presence of two functional groups in amino acids enables them to form complexes with catalysts, function as modifiers, and influence the composition of reaction products. The present study reveals how the liquid-phase homogeneous catalytic oxidation is affected by binary catalyst systems that are composed of cobalt naphthenate and amino acids of various origins (glycine or aminosulfonic acid) as well as individual catalyst, which is cobalt salt 2 (heptadecane olamine) of pentadion acid (CSHPA). The research determines and compares qualitative and quantitative impacts of amino acid additives and individual CSHPA on the oxidation process. The study identifies the regular dependence of CSHPA catalyst on the nature of its previous ultrasound processing. It has been found that the origin of an additive and the alteration of its concentration in a catalytic system permit regulating the quantitative composition of reaction products that result from the liquid-phase oxidation of cyclohexane. The researched catalytic systems can be applied in production to improve its technical and economic indices.

Superoxide dismutase inspired immobilised Ni(II)–protected amino acid catalysts—Synthesis, characterisation, and catalytic activity

Covalently anchored Ni(II)–C-protected amino acid (l-histidine, l-cysteine, and l-cystine) complexes inspired by the active site of the Ni-superoxide dismutase enzyme were synthesised using chloropropylated silica gel as support. The structural features of the surface complexes were studied by the Kjeldahl method and ICP-MS, mid/far IR, UV–vis diffuse reflectance, and X-ray absorption spectroscopies. The enzyme-like activities of the materials were determined in a biochemical test reaction. Covalent grafting and building the complex onto the surface of the support were successful in all cases. It was found that in many instances the structures obtained and the coordinating groups substantially varied upon changing the conditions of the syntheses. All the covalently immobilised Ni(II)-complexes displayed enzyme-like activity. They also were active in the liquid-phase oxidation of cyclohexene, providing the epoxide with high selectivity.

Copper ion substituted hercynite (Cu0.03Fe0.97Al2O4): A highly active catalyst for liquid phase oxidation of cyclohexane

Copper ion substituted MAl2O4 (M=Mg, Mn, Fe, Ni and Zn) spinels, CuxM1−xAl2O4 (x=0.03 and 0.05), have been synthesized by a single step solution combustion method. Of the various compositions studied the 3at.% copper ion substituted hercynite, Cu0.03Fe0.97Al2O4, reported here for the first time, is shown to be much more active (∼92% conversion with ∼99% selectivity) than other spinel analogues towards liquid phase oxidation of cyclohexane in acetonitrile with H2O2 as oxidant in air. Powder XRD analyses have revealed formation of pure hercynite phases. The least-square refined lattice parameters obtained from XRD data together with microstructural data by HRTEM have indicated copper ion substitution in the spinel lattice. The oxidation state of copper has been established as +2 from XPS analysis and it seem to be primarily substituted in the Fe-site of hercynite. Incorporation of the copper in the spinel structure of FeAl2O4 leading to an ionic interaction is explained to be responsible for the higher oxidation activity observed over the combustion synthesized catalyst than the corresponding impregnated catalyst which contains finely dispersed CuO crystallites. Effect of recycling (repeated thrice) has shown almost no degradation of activity of the copper ion substituted hercynite. In contrast, the analogous impregnated catalyst has shown appreciable loss of activity in the consecutive cycles due to the presence of dispersed CuO crystallites which can agglomerate with ease and subsequently leach out.

Highly selective and direct oxidation of cyclohexane to cyclohexanone over vanadium exchanged NaY at room temperature under solvent-free conditions

Vanadium exchanged zeolite Y has been synthesized by simple ion-exchange on NaY and resulting V–Y material has been employed as a heterogeneous catalyst for highly selective and direct one-pot liquid phase oxidation of cyclohexane to cyclohexanone under solvent-free conditions at room temperature. The catalyst (V–Y) has been thoroughly characterized by powder X-ray diffraction (PXRD), N2 sorption, transmission electron microscopic (TEM), Fourier transform infrared (FT IR), UV–visible, X-ray photoelectron spectroscopic (XPS) and atomic absorption spectroscopic (AAS) analyses. The selective oxidation reaction proceeds smoothly over this V-containing heterogeneous catalyst in the presence of tert-butylhydroperoxide (TBHP) as oxidant and the progress of the reaction has been monitored thoroughly by gas chromatographic (GC) and gas chromatography coupled with mass spectrometric (GC–MS) analyses. The recycling efficiency of the V–Y catalyst has been tested by conducting the catalytic reaction repeatedly with the recovered catalyst, where almost retention of the original catalytic activity and selectivity after five reaction cycles has been observed. The effect of oxidant amounts on the catalytic reaction has been studied. Mechanistic pathway for the catalytic reaction over this inexpensive, non-air sensitive, eco-friendly and reusable vanadium exchanged zeolite has been proposed, suggesting future potential of V–Y in solvent-free liquid phase selective oxidation reactions under very mild conditions.

Facile synthesis of highly ordered mesoporous chromium–alumina catalysts with improved catalytic activity and stability

Abstract

Selective oxidation of cyclohexene to adipic acid over silver supported tungsten oxide nanostructured catalysts

We have developed a new synthesis strategy to prepare ∼5 nm metallic silver nanoparticles (AgNPs) supported on tungsten oxide (WO3) nanorods with diameters between 40 and 60 nm in the presence of a cationic surfactant, cetyltrimethylammonium bromide (CTAB). The catalyst was characterized by XRD, XPS, ICP-AES, FT-IR, Raman spectroscopy, EXAFS, SEM and TEM. The catalyst is very effective in liquid phase oxidation of cyclohexene to adipic acid with hydrogen peroxide as an oxidant. The synergy between the surface AgNPs and WO3 nanorods plays the most vital role towards this very high catalytic activity. The reusability of the catalyst which is a prerequisite for practical applications was analysed and it was found that the catalyst exhibits no significant changes in its catalytic activity even after five cycles of reuse. A cyclohexene conversion of >99.9% with an adipic acid selectivity of ∼94% was achieved over ∼5 nm AgNPs supported on the WO3 nanorod catalyst with a very high turnover frequency of ∼12 h−1.

Synthesis and characterization of gold nanoparticles supported on thiol functionalized chitosan for solvent-free oxidation of cyclohexene with molecular oxygen

The selective liquid phase oxidation of cyclohexene to 2-cyclohexe-1-one and 1,2-cyclohexanediol has been investigated over gold nanoparticles (GNPs) with molecular oxygen in a solvent-free condition. The gold nanoparticles were immobilized on thiolated chitosan derivative (TChD), by grafting thiol groups on the support. The catalyst was characterized by XPS, N2 adsorption/desorption, TEM, FT-IR and UV–vis spectroscopy. TEM results show that the majority of Au particles have diameters in the range of 3–6nm. X-ray photoelectron spectroscopy (XPS) revealed the coexistence of both oxidized and metallic gold species on the surface of TChD. The results show that the catalytic performance of GNPs/TChD is quite remarkable and the catalytic activity over recycled catalyst remains at a high level after at least 4 cycles. Activity tests were carried out in an autoclave at 80°C without any solvent. In order to obtain maximum conversion, the reaction parameters such as reaction temperature and time were optimized. Under optimized conditions, a maximum of 87% conversion and 70% selectivity was achieved with the GNPs/TChD catalyst.

Highly Efficient Nano-Catalysts Using Activated Carbon as a Support for One-Step Oxidation of Cyclohexane to Adipic Acid

A new route to substitute for the traditional two-step method for adipic acid production has been investigated. Supported nano metal catalysts Au/C and Co/C were prepared and used for liquid phase oxidation of cyclohexane to adipic acid with oxygen as an oxidant. These catalysts were characterized by XRD, TEM and ICP-AES. The reactions were carried out in an autoclave with solvent and radical initiator at 373~423K and 1.5 MPa. Au/C (1.25%) was found to be a highly efficient catalyst for the oxidation of cyclohexane with a high conversion (44.93%) of cyclohexane and more than 54.85% selectivity to adipic acid. It is indicated that there was a potential application prospect for the nano-catalysts in one-step oxidation of cyclohexane to adipic acid.

Influence of nanoparticles oxidation state in gold based catalysts on the product selectivity in liquid phase oxidation of cyclohexene

Supported gold catalysts Au/TiO2 and Au/ZrO2 were prepared and used for oxidation of cyclohexene with TBHP. These catalysts were characterized by ICP, TEM and diffuse-reflectance UV–vis. The catalytic tests were carried out in liquid phase, at 80°C and at atmospheric pressure.The effects of support and thermal treatment (oxidation state of Au nanoparticles) on catalytic performance were studied. Gold in the catalysts that have been dried is deposited as Auδ+. These catalysts have a high selectivity towards alkene oxides, 81% of 2-cyclohexene-1-ol for Au/TiO2 and 85% of 2-cyclohexene-1-one for Au/ZrO2.

Efficient Allylic Oxidation of Olefins Catalyzed by Polymer Supported Metal Schiff Base Complexes with Peroxides

Three homogeneous Cu(II), Co(II) and Ni(II) complexes of a Schiff base ligand and their heterogeneous complexes supported on poly(4-aminostyrene) were prepared and characterized by using elemental analysis, fourier transform infrared spectroscopy, UV–Vis diffuse reflectance spectroscopy, thermogravimetric analysis and scanning electron microscopy. The catalytic performance of both homogeneous and heterogeneous complexes was evaluated in the liquid phase oxidation of cyclohexene, styrene and trans-stilbene in acetonitrile with tert-butylhydroperoxide or hydrogen peroxide as the oxidant. All types of catalyst were active in oxidation; and, the complexes produce allylic oxidation products in all cases. Immobilized complexes are slightly more active than their homogeneous complexes. The polymer-supported Cu(II) complex shows a higher catalytic activity than the other metal species. The activities of the immobilized catalysts remained nearly the same after five cycles, suggesting the true heterogeneous nature of the catalyst.

Zeolite-Y encapsulated nanohybrid materials: synthesis, spectroscopic characterization, and catalytic significance

The goal of this study is to synthesize zeolite-Y encapsulated nanohybrid materials (ZENMs) of the general formulae [M(VTCH)2]-Y or [M(VFCH)2]-Y (where M = Mn(II), Co(II), Ni(II), and Cu(II); VTCH = vanillin thiophene-2-carboxylic hydrazone; VFCH = vanillin furoic-2-carboxylic hydrazone) and describe their selective catalytic activities. ZENMs are characterized by various physico-chemical techniques, namely ICP-OES, elemental analysis, (FT-IR and electronic) spectral studies, SEMs, X-ray diffraction patterns as well as surface area measurements. The catalytic activities of ZENMs were found to be highly advantageous in yielding significant amounts of cyclohexanone and cyclohexanol in the liquid-phase oxidation of cyclohexane.

Cyclohexane oxidation using Au/MgO: an investigation of the reaction mechanism

The liquid phase oxidation of cyclohexane was undertaken using Au/MgO and the reaction mechanism was investigated by means of continuous wave (CW) EPR spectroscopy employing the spin trapping technique. Activity tests aimed to determine the conversion and selectivity of Au/MgO catalyst showed that Au was capable of selectivity control to cyclohexanol formation up to 70%, but this was accompanied by a limited enhancement in conversion when compared with the reaction in the absence of catalyst. In contrast, when radical initiators were used, in combination with Au/MgO, an activity comparable to that observed in industrial processes at ca. 5% conversion was found, with retained high selectivity. By studying the free radical autoxidation of cyclohexane and the cyclohexyl hydroperoxide decomposition in the presence of spin traps, we show that Au nanoparticles are capable of an enhanced generation of cyclohexyl alkoxy radicals, and the role of Au is identified as a promoter of the catalytic autoxidation processes, therefore demonstrating that the reaction proceeds via a radical chain mechanism.