Heterogeneous Catalyst For Epoxidation Research Articles

Catalytic epoxidation of alkenes with 30% H2O2 over Mn2+-exchanged zeolites

The Mn2+-exchanged zeolites Mn-Y, Mn-beta, Mn-A and Mn-ZSM-5 were prepared and used as heterogeneous catalysts for the liquid phase epoxidation of alkenes with aqueous hydrogen peroxide (30% H2O2) at 273–298 K in the NaHCO3 buffer system. The structures of catalysts were characterized by powder X-ray diffraction (XRD), UV–vis, ICP, BET and IR techniques. Mn-beta and Mn-Y exhibited the best recyclable activity for the epoxidation of styrene to achieve styrene conversions higher than 96.0 and 98.5 mol%, respectively. Mn-beta showed higher activity for cyclohexene and norbornene but lower activity for α-methylstyrene, cinnamyl chloride, indene, cyclooctene and α-pinene than Mn-Y, which could be correlated with the difference of their pore sizes. However, these catalysts did not show any activity for the epoxidation of 1-octene with H2O2, possibly due to low electron density of double bonds of linear terminal alkenes.

The catalytic function of SiO 2-immobilized Mn(II)-complexes for alkene epoxidation with H 2O 2

Two symmetrical acetylacetone-based Schiff bases were immobilized on a silica surface by grafting and sol–gel procedure. The corresponding supported manganese complexes were prepared and evaluated as heterogeneous catalysts for alkene epoxidation with H 2O 2. These heterogeneous catalysts show remarkable effectiveness and selectivity towards epoxide formation in the presence of ammonium acetate. Moreover, the developed heterogeneous catalysts preserve the coordination and catalytic properties of the active-homogeneous manganese catalysts for alkene epoxidation vs. the competitive H 2O 2 dismutation. EPR spectroscopy shows that in heterogeneous manganese catalysts the Mn 2+ centers are in a flexible, non-tight, coordination environment, as in the corresponding homogeneous manganese catalysts. However, after a first use of the heterogeneous catalysts, the Mn centers are detached from the ligand and are randomly dispersed on the SiO 2 surface. This is responsible for the loss of catalytic activity.

Styrene Epoxidation over Carbon Nanotube-Supported Gold Catalysts

Carbon nanotube supported gold catalysts prepared by deposition–precipitation with urea (DP urea) were characterized by various techniques. Its catalytic activity was examined for the oxidation of styrene using t-butylhydroperoxide as oxidant. This system showed good epoxide selectivity. The other factors, such as solvent, reaction time, concentrations of oxidant and catalyst, have also been investigated and reaction conditions are optimized. It is a novel highly active/selective and reusable heterogeneous catalyst for styrene epoxidation.

Layered Transition Metal Carboxylates: Efficient Reusable Heterogeneous Catalyst for Epoxidation of Olefins

Layered metal carboxylates [M(malonato)(H(2)O)(2)](n) (M = Ni(II) and Mn(II)) that have a claylike structure have been synthesized hydrothermally and characterized. The interlayer separation in these layered carboxylates is comparable to that of the intercalation distance of the naturally occurring clay materials or layered double hydroxides (LDHs). In this study, we have demonstrated that, instead of intercalating the metal complex into layers of the clay or LDH, layered transition metal carboxylates, [M(malonato)(H(2)O)(2)](n), as such can be used as a recyclable heterogeneous catalyst in olefin epoxidation reaction. Metal carboxylates [M(malonato)(H(2)O)(2)](n) exhibit excellent catalytic performance in olefin epoxidation reaction.

Manganese(III) porphyrin supported on multi-wall carbon nanotubes: A highly efficient and reusable biomimetic catalyst for epoxidation of alkenes with sodium periodate

In this paper, the biomimetic epoxidation of alkenes catalyzed by tetrakis( p-aminophenyl)porphyrinatomanganese(III) chloride, [Mn(TNH 2PP)Cl], supported on functionalized multi-wall carbon nanotubes, MWCNT, is reported. The catalyst, [Mn(TNH 2PP)Cl-MWCNT], was used as an efficient and heterogeneous catalyst for epoxidation of alkenes with NaIO 4 at room temperature, in the presence of imidazole as an axial ligand. This new heterogenized catalyst was characterized by elemental analysis, FT IR spectroscopy, diffuse reflectance UV–Vis spectrophotometry, scanning electron microscopy and transmission electron microscopy. The biggest advantage of Mn(TNH 2PP)Cl-MWCNT is its high reusability in the oxidation reactions, in which the catalyst was reused several times without significant loss of its catalytic activity.

Photovoltaic activity of Ti/MCM‐41

Ti/MCM-41 is a well-known heterogeneous catalyst for alkene epoxidation with organic peroxides. This titanosilicate contains isolated titanium atoms forming part of a framework of mesoporous silica whose structure is formed by parallel hexagonal channels 3.2 nm in diameter. The surface area and porosity of Ti/MCM-41 are about 880 m(2) g(-1) and 0.70 cm(3) g(-1), respectively. These values are among the highest for any material. Herein, we show that Ti/MCM-41 exhibits photovoltaic activity. Dye-sensitized solar cells using mesoporous Ti/MCM-41 (2.8-5.7 % Ti content) as active layer, black dye N3 as photosensitizer and I(3) (-)/I(-) in methoxyacetonitrile as electrolyte exhibit a V(OC), J(SC) and FF of 0.44 V, 0.045 mA cm(-2) and 0.33, respectively. These values compare well against 0.75 V, 4.1 mA cm(-2) and 0.64, respectively, measured for analogous solar cells using conventional P-25 TiO(2). However, the specific current density (J(SC)/Ti atom) for the Ti/MCM-41 is very similar to that of P25 TiO(2).

Styrene epoxidation over Ag-γ-ZrP catalyst prepared by ion-exchange

A hybrid complex Zr(PO4)(AgHPO4) was prepared by ion-exchange and was determined using elemental analysis, X-ray diffraction (XRD), Fourier transformed-infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and other instruments. Its catalytic activity was examined on the oxidation of styrene using t-butylhydroperoxide (TBHP) as oxidant under argon atmosphere, this system showed good epoxidation selectivity, the other factors, such as solvent, reaction time, concentrations of oxidant and catalyst, also have been investigated and reaction conditions are optimized. It is a novel highly active/selective and reusable heterogeneous catalyst for styrene epoxidation, while this catalytic system showed no epoxidation selectivity but good enol selectivity for cycloolefins with allylic H.

Jacobsen catalyst anchored onto modified carbon xerogel as enantioselective heterogeneous catalyst for alkene epoxidation

Two types of carbon xerogels were prepared using two different methodologies where the pH of the solution during the sol–gel processing, formaldehyde/resorcinol ratio and the drying method, were varied (01CX and 02CX). The samples show distinct textural properties: 02CX material has higher mesopore area and micropore volume than 01CX, but the pore radius of the latter material is three times larger than the former. Activation of the materials under 5% O 2 (in N 2) at 440 °C introduces surface oxygen groups, mainly phenol and carbonyl/quinone groups with small quantities of carboxylic anhydrides. Treatment with sodium hydroxide solution converted the phenol groups into phenolates and promotes hydrolysis of carboxylic anhydrides into carboxylates. A modified Jacobsen catalyst was directly immobilised via axial coordination of the Mn(III) metallic centre onto the phenolate/carboxylate groups of the sodium modified carbon xerogels. The catalysts were tested in the asymmetric epoxidation of styrene, α-methylstyrene and 6-cyano-2,2-dimethylchromene using m-CPBA/NMO, NaOCl or PhIO as oxygen sources. The catalysts show some activity and enantioselectivity, eventhough loss of Mn is evident. Blank runs involving the carbon xerogel and the oxidants suggest that the oxidants do not attack the surface hydroxyl groups responsible for the metal complex immobilisation.

Grafting polyethylene glycols molybdenum(VI) complexes on ZSPP and their catalytic epoxidation of cyclohexene

Abstract A new type of inorganic–organic hybrid materials – zirconium oligo-styrenyl phosphonate hydrogen phosphate (ZSPP) was used to prepare heterogeneous catalysts for olefin epoxidation by grafting polyethylene glycols on ZSPP and subsequently coordinating with MoO 2 (acac) 2 . The catalysts were characterized by IR, Raman, XPS, XRD, TG, BET and elemental analysis. The catalytic activities of the prepared catalysts were evaluated through the epoxidation of cyclohexene using TBHP as oxidant. The results indicated that conversion and selectivity increased at first and then decreased with increasing numbers of O atoms in the ligands, and the catalyst 2b gave the best catalytic results that the conversion and selectivity was up to 98.9% and 97.4%, respectively.

Bifunctional Heterogeneous Catalysts for Selective Epoxidation and Visible Light Driven Photolysis: Nickel Oxide‐Containing Porous Nanocomposite

Bifunctional Heterogeneous Catalysts for Selective Epoxidation and Visible Light Driven Photolysis: Nickel Oxide‐Containing Porous Nanocomposite

Bis(catechol)salen]MnIII Coordination Polymers as Support‐Free Heterogeneous Asymmetric Catalysts for Epoxidation

AbstractThe formation of coordination polymers by the reaction of [bis(catechol)salen]MnIII with several di‐ and trivalent metal ions is reported. These polymers are insoluble in a wide range of organic solvents and water but can be dissolved upon addition of excess pyrocatechol. They function as enantioselective heterogeneous epoxidation catalysts and exhibit catalytic activity comparable to that of the homogeneous[bis(catechol)salen]MnIII building block alone when used for the enantioselective epoxidation of 2,2‐dimethyl‐2H‐chromene. After catalysis, catalyst isolation from the reaction mixture can be readily achieved by centrifugation and decantation. Under practical oxidant concentrations, the catalyst can be recycled up to ten times with little loss of activity and no loss of enantioselectivity. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Transition-metal-free microporous and mesoporous catalysts for the epoxidation of cyclooctene with hydrogen peroxide

Transition-metal-free microporous and mesoporous materials were studied as heterogeneous epoxidation catalysts. MCM-41-type materials and zeolites with various porous structures and aluminium or gallium content but devoid of any transition metal were prepared and tested in the epoxidation of cyclooctene with aqueous hydrogen peroxide. The most promising catalytic results were obtained with Al-MCM-41, Ga-MCM-41, and ultra-stable zeolite Y (USY) with a low Si/Al ratio. All of these catalysts have acid sites of moderate strength. With Ga-MCM-41, 95% conversion of cyclooctene with 96% selectivity toward the epoxide was reached after 24 h of reaction. The catalyst could be recycled with no loss of catalytic properties.

Novel Transition‐Metal‐Free Heterogeneous Epoxidation Catalysts Discovered by Means of High‐Throughput Experimentation

Various transition-metal-free oxides have been studied as catalysts for the epoxidation of cyclooctene with hydrogen peroxide by means of high-throughput experimentation. Different boron, aluminium, and gallium oxides were prepared according to various synthesis methods. A number of pure aluminium and gallium oxides showed very good catalytic performances, while the results obtained with boron oxides or mixed oxides were less positive. The best results were obtained with a gallium oxide catalyst, which gave an epoxide yield of 71 % and a selectivity of 99 % after reaction for 4 h at 80 degrees C. Gallium oxides had not been reported previously as active epoxidation catalysts. The use of high-throughput experimentation proved useful both for discovering new active catalysts and for identifying a number of relationships between the synthesis conditions and the catalytic properties of the transition-metal-free oxides.

Low‐Basicity Oxygen Atoms: A Key in the Search for Propylene Epoxidation Catalysts

Gotta have copper: DFT studies indicate that the performance of heterogeneous epoxidation catalysts depends on the first step in the reaction between oxygen atoms and propylene molecules coadsorbed on the metal surface (see picture; C yellow, H light blue, O red). The high basicity of oxygen atoms on silver favors allylic hydrogen stripping, whereas the low basicity of oxygen atoms on copper favors metallacycle formation and subsequent epoxidation.

A new type of heterogeneous epoxidation catalysts polyamines molybdenum (VI) complexes grafted on zirconium oligo-styrenyl phosphonate hydrogen phosphate

A new type of inorganic–organic hybrid materials — zirconium oligo-styrenyl phosphonate hydrogen phosphate (ZSPP) was designed and synthesized. Four kinds of new heterogeneous catalysts for olefin epoxidation were obtained by grafting polyamines on ZSPP and subsequently coordinating with MoO 2(acac) 2. The catalysts were characterized by IR, Raman, XPS, XRD and elemental analysis. The catalytic activities of the prepared catalysts were evaluated through the epoxidation of cyclohexene using TBHP as oxidant. The results revealed that these catalysts possessed high conversion, selectivity and reusability, but with increasing numbers of nitrogen atoms in ligands, the conversion and selectivity gradually decreased.

Supported metalloporphyrincatalysts for alkeneepoxidation

This review is devoted to the recent advances in the preparation of immobilised metalloporphyrins and their use as heterogeneous catalysts for alkene epoxidation. The wide range of supports, nature of attachments, and metalloporphyrins that have been reported is detailed and a comparison is made between the activities of the resulting catalysts in the epoxidation of different alkenes. The important issue of recyclability of the metalloporphyrins is also covered.

Heterogeneous Catalyst for Enantioselective Epoxidation of α,β-Unsaturated Ketones

Heterogeneous Catalyst for Enantioselective Epoxidation of α,β-Unsaturated Ketones

Chiral manganese(III) Schiff base complexes anchored onto activated carbon as enantioselective heterogeneous catalysts for alkene epoxidation

Two chiral manganese(III) salen catalysts, bearing different chiral diamine bridges, were anchored by direct axial coordination of the metal centre onto the phenolate groups of a modified commercial activated carbon. The modification of the activated carbon was achieved by reaction between sodium hydroxide and surface phenol groups giving rise to phenolate groups (CoxONa), which were characterised by XPS, TG and TG-IR. Characterisation of immobilised manganese(III) salen catalysts onto CoxONa material by XPS, ICP-AES and TG-IR clearly point to reaction between carbon surface phenolate groups and the manganese(III) complexes through axial coordination of the metal centre to these groups. These materials were active and enantioselective in the epoxidation of styrene and α-methylstyrene in dichloromethane at 0 °C using, respectively, m-CPBA/NMO and NaOCl. Only for α-methylstyrene comparable asymmetric inductions were found in the epoxide as the homogeneous phase reactions and catalyst reuse led to no significant loss of catalytic activity and enantioselectivity.

Simple Metal Oxides as Efficient Heterogeneous Catalysts for Epoxidation of Alkenes by Molecular Oxygen.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Peroxotungstate Immobilized on Ionic Liquid-Modified Silica as a Heterogeneous Epoxidation Catalyst with Hydrogen Peroxide

Peroxotungstate immobilized on ionic liquid-modified SiO2 is capable of heterogeneously epoxidizing a wide range of olefins with the maintenance of the catalytic activity of homogeneous analogue. The epoxidation was immediately stopped by the removal of the catalyst, and no tungsten species could be found in the filtrate after the removal of the catalyst. These results can rule out any contribution to the observed catalysis from the tungsten species that leached into the reaction solution, and the observed catalysis is truly heterogeneous in nature. Furthermore, the catalyst was reusable without the loss of the catalytic performance.