Catalysts For Epoxidation Of Cyclohexene Research Articles

Shape-controlled nanostructured MoO3/CeO2 catalysts for selective cyclohexene epoxidation

This study reported a vital role of CeO2 shape on the structure-activity properties of MoOx/CeO2 catalysts for cyclohexene epoxidation. Uniform dispersion of MoOx on the surface of shape-controlled CeO2 nanocubes (average particle size: 23.5 nm) and nanorods (average width: 6.3 nm and length: 15–95 nm) was found in MoOx/CeO2 nanomaterials. The MoOx/CeO2 nanocubes showed higher epoxide selectivity (97.3%) with 98.9% cyclohexene conversion, although it has lower BET surface area (30.2 m2/g) compared with MoOx/CeO2 nanorods (72.8 m2/g). The presence of more electropositive Mo6+ species and the strong Mo-Ce interaction led to improved catalytic efficacy of MoOx/CeO2 nanocubes in cyclohexene epoxidation.

Homo and Hetero Trinuclear Metal Clusters of Co, Mn and Co/Mn Hybrid Materials as Catalysts for Epoxidation of Cyclohexene

Trinuclear metal clusters of Co, Mn, and Co/Mn hybrid of [Mn3(O)(CH3COO)6-(py)3ClO4], [Co3(O)(CH3COO)6-(py)3ClO4], [Co2Mn(O)(CH3COO)6-(py)3ClO4], and [CoMn2(O)(CH3COO)6-(py)3ClO4] were prepared and characterized by FT-IR and UV–Vis spectroscopic techniques. These homogeneous catalysts were investigated in the epoxidation of cyclohexene in the presence of H2O2/O2 under mechanical stirring conditions. The effect of the oxidant, reaction temperature, kind of promoter, and solvent system were investigated on conversion and epoxide selectivity. In these systems, NaBr was selected as a promoter of oxidation based on standard potential (X = Cl−, Br−) toward Co3+, and Mn3+. These homogeneous catalytic systems can be the perfect choice for epoxidation of cyclohexene with good conversion and high epoxide selectivity over short periods.

Cobalt imine–pyridine–carbonyl complex functionalized metal–organic frameworks as catalysts for alkene epoxidation

Aerobic epoxidation of alkene is a green and economical route to produce epoxides. For such reaction, transition metal complexes exhibit favorable catalytic activity. In this work, NH2-MIL-101, a stable metal–organic framework (MOF) material with large surface area and high pore volume, was functionalized with pyridine-2,6-dicarbaldehyde and Co(NO3)2, to realize the immobilization of Co(II) via imine–pyridine–carbonyl (N,N,O) tridentate ligands bonding to MOF skeleton. The modified materials were applied as heterogeneous catalysts for the aerobic epoxidation of cyclohexene at ambient temperature, and multiple factors were studied to explore their influences on catalytic effects. Under the optimal reaction conditions, satisfactory substrate conversion and epoxide selectivity were reached. In addition, this catalytic system is suitable for a variety of alkene substrates. Furthermore, recycle experiments and infrared spectroscopy characterization illustrated that the coordination surroundings of Co are altering smoothly during the reaction process, thus having an impact on the performance of catalyst.

Magnetic polymer microspheres based on phosphotungstic acid quaternary ammonium salt as an efficient heterogeneous catalyst for epoxidation of cyclohexene

The magnetic polymer microsphere catalysts based on phosphotungstic acid quaternary ammonium salt were designed and prepared in order to improve the performance and reusability of the catalysts during the epoxidation of cyclohexene. The structure, particle size and surface property of the new catalysts were characterized by FTIR, laser particle size analysis and SEM, respectively. And the reactivity of the catalysts was detected in cyclohexene epoxidation. Among the obtained catalysts, PS-double-D-PW4 catalyst exhibited the best catalytic performance and high stability for cyclohexene epoxidation. The results showed that the optimum yield of epoxycyclohexane was 83% with a selectivity above 95% after 7 h. And the catalyst still showed a conversion above 78% after six runs.

Optimization of mesoporous titanosilicate catalysts for cyclohexene epoxidation via statistically guided synthesis

An efficient approach to improve the catalytic activity of titanosilicates is introduced. The Doehlert matrix (DM) statistical model was utilized to probe the synthetic parameters of mesoporous titanosilicate microspheres (MTSM), in order to increase their catalytic activity with a minimal number of experiments. Synthesis optimization was carried out by varying two parameters simultaneously: homogenizing temperature and surfactant weight. Thirteen different MTSM samples were synthesized in two sequential ‘matrices’ according to Doehlert conditions and were used to catalyse the epoxidation of cyclohexene with tert-butyl hydroperoxide. The samples (and the corresponding synthesis conditions) with superior catalytic activity in terms of product yield and selectivity were identified. In addition, this approach revealed the limiting values of each synthesis parameter, beyond which the material becomes catalytically ineffective. This study demonstrates that the DM approach can be broadly used as a powerful and time-efficient tool for investigating the optimal synthesis conditions of heterogeneous catalysts.

Comparative Study of Titanium-modified HMS Mesoporous Materials via Different Preparing Methods

The current work is focused on the testing of titanium modified hexagonal mesoporous silica (HMS) for catalysts in epoxidation of cyclohexene. Two samples were prepared via the chemical liquid deposition (CLD) and the chemical vapor deposition (CVD), namely Ti/HMS-L and Ti/HMS-V, respectively. HMS and Ti/HMS were characterized by XRD, N2-adsorption, ICP-AES, UV-Vis. The samples were also evaluated by the epoxidation of cyclohexene with cumene hydroperoxide (CHP) as oxidant. It is revealed that Ti/HMS samples possess typical hexagonal mesoporous structure in which most of titanium species exist in the form of framework tetracoordinated state. Meanwhile, Ti/HMS-V is more seriously affected than Ti/HMS-L since the former was prepared at higher temperature. Ti/HMS-V gives more excellent catalytic performance than Ti/HMS-L, which is likely because the former has more isolated and framework titanium species. Either Ti/HMS-V or Ti/HMS-L can be used only 1 time in epoxidation experiment.

Vanadia loaded hierarchical ZSM-5 zeolite: a promising catalyst for epoxidation of cyclohexene under solvent free condition

Hierarchical ZSM-5 zeolite with composite micro and mesoporous was obtained by alkali treatment of parent ZSM-5 for 60 min. Vanadia was loaded on modified zeolite by wetness impregnation technique (VDZ). The prepared samples were characterized by various techniques including XRD, FTIR, TGA, UV-DRS, TEM, XPS and nitrogen adsorption–desorption. Vanadia loaded sample was found to exhibit excellent catalytic activity for the epoxidation of cyclohexene by tertiary butyl hydroperoxide. A controlled reaction was carried out to demonstrate the utility of hierarchical topology of the catalyst. A free radical mechanism was proposed for the reaction with rate constant of 6.91 × 10−2 L mol−1 min−1 and activation energy of 41.81 kJ mol−1. The reaction was carried out without the use of any solvent and the catalytic activity of VDZ was retained even after five runs.

Aerosol-assisted synthesis of hierarchical porous titanosilicate molecular sieve as catalysts for cyclohexene epoxidation

Hierarchical titanosilicate composites (HTS) have been synthesized by an aerosol spray method, by which TS-1 nanoparticles were assembled with cetyl trimethyl ammonium bromide and tetraethylorthosilicate/tetra-n-butyl titanate to form a hierarchical porous composites with a core–shell structure. The structure, porosity, morphology and composition of the materials were characterized by X-ray diffraction, nitrogen adsorption isotherm, Raman spectroscopy, electron microscopy and X-ray fluorescence spectroscopy. The hierarchical porous molecular sieve combines the advantages of TS-1 and Ti-KIT-1, and shows high activity and selectivity to epoxide in cyclohexene epoxidation with H2O2. The yield of cyclohexene oxide on HTS is much higher than those on TS-1 and Ti-KIT-1. The selectivities to cyclohexene oxide and 1,2-cyclohexanediol can be adjusted by varying the titanium contents of the HTS samples.

Novel vanadium-chromium-bentonite green catalysts for cyclohexene epoxidation

The aim of this work is the valorization of bentonite-type clay from Maghnia (Algeria) as green catalyst for the production of added value fine chemicals. The modification of the clay structure by acid activation and impregnation of transition metals, such as chromium and vanadium, enhanced redox properties and increased Lewis and Brønsted acidity. Various samples of vanadia supported on chromium-containing acid-activated bentonite, were prepared and characterized by diffuse-reflectance UV–vis spectroscopy, surface acidity followed by FT-IR, X-ray diffraction, nitrogen adsorption–desorption isotherms and scanning electron microscopy (SEM) coupled with EDX. The catalysts prepared were studied in the cyclohexene epoxidation, using tert-butyl hydroperoxide as oxidant. The influences of vanadium content, catalyst weight, reaction temperature and oxidant amount on the evolution of the epoxidation reaction were checked. The experimental results showed an interesting catalytic activity of 43% and a selectivity towards epoxide of about 71%, when TBHP was used as oxidant and heptane as solvent.

Zirconium phenylphosphonate-anchored methyltrioxorhenium as novel heterogeneous catalyst for epoxidation of cyclohexene

Epoxidation of olefins to epoxides is widely recognized as an important unit process in the manufacture of fine chemicals and intermediates. Developing an environmentally benign heterogeneous catalytic system for olefin epoxidation with high activity and selectivity is still a challenge in this research field. Herein, we report our attempts to synthesize novel zirconium phenylphosphonate-anchored methyltrioxorhenium (MTO/ZrPP) heterogeneous catalysts by a conventional impregnation method and evaluate their catalytic performance for epoxidation of cyclohexene using urea–hydrogen peroxide adduct (UHP) as oxidant without the addition of base ligands. The MTO/ZrPP catalyst samples are characterized by powder X-ray diffraction (XRD), Fourier transform infrared (FT-IR), inductively coupled plasma emission spectrometry (ICP-ES), high resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and solid-state 1H magic-angle spinning nuclear magnetic resonance (1H MAS NMR) techniques. Meanwhile, the density functional theory (DFT) calculation is carried out to further understand the structure feature and interactions of the MTO/ZrPP catalyst. It is revealed that MTO is anchored on support surface by the favored hydrogen-bonding interaction between two oxo ligands of MTO and two H atoms from the adjacent phenyls of ZrPP. MTO/ZrPP catalyst displays excellent catalytic activity for cyclohexene epoxidation. Moreover, only cyclohexene oxide production can be obtained under the employed reaction conditions.

Tuning the olefin epoxidation by manganese(iii) complexes of bisphenolate ligands: effect of Lewis basicity of ligands on reactivity

A new family of manganese(iii) complexes of the type [Mn(L)Cl], where H2L is 1,4-bis(2-hydroxy-benzyl)-1,4-diazepane (), 1,4-bis(2-hydroxy-4-methylbenzyl)-1,4-diazepane (), 1,4-bis(2-hydroxy-3,5-dimethylbenzyl)-1,4-diazepane () and 1,4-bis(2-hydroxy-3,5-di-tert-butylbenzyl)-1,4-diazepane (), has been isolated and studied as a catalyst for epoxidation reaction. Complexes have been characterized using elemental analysis, electronic spectral and electrochemical methods and ESI-MS. The single crystal X-ray structures of and contain the MnN2O2Cl chromophore with a novel square pyramidal coordination geometry (τ: , 0.11; , 0.00). All the complexes possess a distorted square pyramidal coordination geometry in solution, as revealed by the characteristic bands observed in the electronic spectra. A time dependent density functional theory (TD-DFT) calculation has been performed to assist in the assignment of the electronic absorption spectral bands of the complexes. The Mn(iii)/Mn(ii) redox potentials (E1/2) of fall within the narrow range of 0.279-0.320 V. The catalytic ability of the complexes towards olefin epoxidation has been investigated using PhIO as the oxygen source at room temperature under an N2 atmosphere. Addition of N-methylimidazole to the reaction mixture leads to an increase in the epoxide yield. A correlation between the Lewis acidity of the Mn(iii) center as tuned by the substituents on the phenolate ligand, and the epoxide yield and product selectivity has been observed. The present complexes act as better chemoselective catalysts for epoxidation of cyclohexene and styrene rather than cyclooctene.

Novel pyridine Schiff base–manganese(ii) complexes: synthesis, characterization and catalytic reactivity of the epoxidation of cyclohexene

Four novel pyridine Schiff bases derived from 2,6-pyridinedicarbaldehyde and substituted o-hydroxyl-aromatic amines and their manganese(II) complexes were synthesized and characterized by elemental analyses, ESI-MS analysis, thermal analysis (TGA), H-NMR, IR and UV-vis. The activity of these complexes as catalysts in cyclohexene autoxidation were investigated and the effects of various reaction conditions on the catalytic reaction were optimized to obtain as high as 99.6% conversion with 95.0% selectivity of epoxycyclohexane at 40 °C for 6 h using molecular oxygen as an oxidant in acetonitrile. The result presents excellent catalysts for epoxidation of cyclohexene under mild temperature and atmospheric oxygen (O2) pressure.

Synthesis, characterization and catalytic performance of Mo-TUD-1 catalysts in epoxidation of cyclohexene

A new, 3-D mesoporous amorphous molybdenum-containing silica, denoted Mo-TUD-1, was prepared with variable Mo-loading via direct hydrothermal treatment using triethanolamine as a template. Elemental analysis, N2 sorption measurements, NMR spectroscopy, XRD, UV-Vis spectroscopy, SEM, HR-TEM, and Raman spectroscopy indicated that as a function of increasing loading, the morphology of Mo changes from isolated sites to nano particulates, and finally to crystalline MoO3 at a loading higher than 5 wt%. The catalytic performance of the Mo-TUD-1 samples was investigated in the liquid phase epoxidation of cyclohexene with TBHP as an oxidant. Mo-TUD-1 with a low molybdenum loading showed a higher TON as compared to samples with a high loading, suggesting that isolated Mo-sites are more active than particulate MoO3. Stability and reusability of the catalyst containing isolated sites were also investigated. While leaching was observed initially, stable performance was obtained in as many as three subsequent catalytic runs

Transition metal coordination polymers MeX 2(4,4′bipyridine) (Me = Co, Ni, Cu; X = Cl −, CH 3OCO −, acetylacetonate) selective catalysts for cyclohexene epoxidation with molecular oxygen and isobutyraldehyde

This paper presents aspects concerning the catalytic activity of several transition metal coordination polymers with the general formula 2 ∞[Me(II)X 2(4,4′bipyridine)] (Me(II) = Co, Ni, Cu; X = Cl −, CH 3OCO −, and acetylacetonate) towards the epoxidation of cyclohexene with molecular oxygen in the presence of isobutyraldehyde as reductant. The obtained results proved that all the investigated catalysts showed a high selectivity for epoxidation (over 88%). The conversion of cyclohexene was found to depend on the nature of both the transition metal cation and the ligand X. The most active catalyst was found to be 2 ∞[Co(II)(CH 3OCO) 2(4,4′bipyridine)].

Styrene–hydroxyethyl methacrylate copolymer microsphere immobilized porphyrinatomanganese(III) as a mild, reusable and highly efficient catalyst for epoxidation of cyclohexene with molecular oxygen

On the basis of synthesis of styrene–hydroxyethyl methacrylate copolymer microspheres with a functionalized hydroxyl, we have prepared a new type of copolymer microspheres immobilized porphyrinatomanganese(III), P(St-co-HEMA)MnP, by a condensation reaction between a hydroxyl in copolymer microspheres surface and a carboxyl in porphyrin ring. The obtained copolymer catalyst (P(St-co-HMEA)MnP) was characterized by SEM, UV–vis, IR, ICP and TG–DTG. The SEM image shows that the morphology of the copolymer catalyst is spheriform with ca. 4 μm diameter. The catalytic activity of P(St-co-HMEA)MnP to epoxidize cyclohexene in the presence of molecular oxygen and isobutylaldehyde has been studied. The catalytic efficiency of P(St-co-HMEA)MnP is comparable to that of non-supported MnCMPTTP. It is a mild, reusable and highly efficient heterogeneous catalyst for the epoxidation of cyclohexene.

Tripodal titanium silsesquioxane complexes immobilized in polydimethylsiloxane (PDMS) membrane: Selective catalysts for epoxidation of cyclohexene and 1-octene with aqueous hydrogen peroxide

We investigated the activity, epoxide selectivity, H 2O 2 efficiency, and recyclability of heterogeneous alkene epoxidation catalysts prepared by encapsulation of tripodal Ti silsesquioxane complexes in polydimethylsiloxane (PDMS) membrane. We found that [Ti(NMe 2){( c-C 6H 11) 7Si 7O 12}]/PDMS ( 3) and [Ti(NMe 2){( i-C 4H 9) 7Si 7O 12}]/PDMS ( 4) displayed high activity, epoxide selectivity (⩾97%), and H 2O 2 efficiency (⩾97%) in cyclohexene- and 1-octene epoxidation with aqueous H 2O 2. Moreover, these catalysts were highly recyclable. The high H 2O 2 efficiency can be attributed to the uniformly non-polar environment provided about the Ti silsesquioxane complex in 3 and 4 by the PDMS membrane, which presumably results in low local water concentrations and higher [alkene]:[H 2O 2] ratios at the Ti center than in the bulk reaction medium; both of these effects favor the epoxide selectivity and minimal leaching of titanium. Our study of the effect of solvent on catalyst activity revealed that acetonitrile is to be preferred as solvent, since methanol inhibits the epoxidation at long reaction times.

Synthesis of Titanium-Containing Mesoporous Silicas as Catalysts for Cyclohexene Epoxidation

Ti-containing mesoporous materials have been prepared by hydrothermal synthesis at 100 °C with two different Si/Ti ratios (20 and 60) in the synthesis mixture. A detailed study about the effect of synthesis time on the physicochemical properties of the materials has been carried out. The samples were characterized by XRD, DRUVvis, N2 adsorption, and pyridine adsorption analyzed by FT-IR. The samples synthesized using the lower Si/Ti ratio presented the higher titanium incorporation and the higher acid character. The synthesis time appears as an important parameter that affects the textural, structural, chemical, and acid properties of the final solids. For the lower Si/Ti ratio, a longer synthesis time is needed to obtain a more ordered structure. However, in both cases, short synthesis times do not allow a proper incorporation of titanium into the silica framework, which is reached with synthesis times of about 3 days. The results of catalytic activity indicate that the solids studied here present an int...

Synthesis of novel dioxomolybdenum(VI) complexes bearing ferrocenyldiimine and their catalytic performances in olefin epoxidation

Novel dioxomolybdenum(VI) complexes bearing bis(ferrocenylcarbaldimine) ligands were prepared in good yield and characterized by spectroscopy and elemental analysis. The complexes were found to be excellent catalysts for the homogeneous epoxidation of cyclohexene and styrene using tert-butyl hydroperoxide (TBHP) as oxidant. The complexes can be recovered and reused.

Synthesis, characterization and activity in cyclohexene epoxidation of mesoporous TiO2–SiO2 mixed oxides

Abstract A series of porous TiO 2 –SiO 2 mixed metal oxides were synthesized via sol–gel route using n -alkyl amine as pore directing templates. The mixed oxides were characterized by nitrogen physisorption for surface area, pore volume and pore size distribution, as well as by FTIR, TGA, SEM, and TEM for the dispersion of titanium. These compounds are good catalysts for liquid phase epoxidation of cyclohexene using hydrogen peroxide as the oxidant. The effects of various factors on catalyst reactivity were also studied. The catalysts performance and selectivity are enhanced in protic solvents when compared to aprotic solvents.

Nickel(macrocycle) Complexes Immobilized within Montmorillonite and MCM-41 as Catalysts for Epoxidation of Olefins

In this study, we have investigated the role of immobilized Ni(II) complexes with macrocyclic ligands of 1,8-dimethyl-1,3,6,8,10,13-hexaazacyclotetradecane (L) and 1,8-dibenzyl-1,3,6,8,10,13-hexaazacyclotetradecane (L′) within montmorillonite and MCM-41 as catalysts for epoxidation of cyclohexene, cyclopentene, norbornene, styrene and α-methylstyrene with tert-butylhydroperoxide (TBHP). The yield of epoxide in a given period depends mainly on the reaction rate of the complex with TBHP which is greatly affected by the alkene structure, ligand type and solid support. No desorption was observed during the course of reaction. Some mechanistic points will be presented in this article.