Selective Epoxidation Of Styrene Research Articles

Ultra‐low Mn(salen) supported on lignin and selective epoxidation of olefins

AbstractPrecise design of highly efficient, low metal load and eco‐friendly catalysts is the key to sustainable catalysis and green chemistry. In this work, we develop an ultra‐low loading of Mn(salen) complexes covalent grafted with lignin and applied in the selective epoxidation of olefins using O2 as an oxidant. Lignin not only provides the Mn(salen) graft sites but also promotes substrate enrichment via the π‐stacking interaction between substrate and supports. In particular, high turnover frequencies (TOF) of 1833 h−1 can be obtained for styrene epoxidation under mild conditions, which can be superior to most reported Mn(salen) supported catalysts. Compared with cellulose, the lignin‐based catalysts exhibit a higher selectivity toward styrene oxide during the epoxidation of styrene under mild conditions. Controlled experiments indicate that the synergistic effect between phenolic hydroxyl groups and the Mn(salen) complex can improve the conversion rate and selectivity during the selective epoxidation of styrene. This work designs a series of lignin‐based catalysts with ultra‐low Mn(salen) loading, which broadens the utilization of lignin and gives enlightenment for the rational design of lignin‐based catalysts.

Dimeric copper(II) tetracarboxylates as catalysts in the selective epoxidation of styrene

Dicopper(II) tetracarboxylate complexes of the type [Cu2(µ-O2CR)4L2] have received a great deal of attention from inorganic chemists in the past. However, these well-known species have been rarely studied as catalysts. Herein we describe the synthesis, UV–Vis spectral behavior and catalytic properties of six species of this type, viz. [Cu2(µ-O2CC6H5)4(py)2] (I), [Cu2(µ-O2CC6H5)4(4-CNpy)2] (II), [Cu2(µ-O2CC6H5)4(3-CNpy)2] (III), [Cu2(µ-O2CCH3)4(py)2] (IV), [Cu2(µ-O2CC7H15)4(4-CNpy)2] (V) and [Cu2(µ-O2CC7H15)4(3-CNpy)2] (VI). As evidenced by their solid state and solution UV–Vis spectra, these complexes retain their dinuclear integrity in solution and therefore they have been investigated as homogenous catalysts for styrene epoxidation. They exhibit very good to excellent catalytic activities towards the oxidation of styrene with aqueous tert-butylhydroperoxide (TBHP) as the terminal oxidant. The reactions give styrene oxide (SO) and benzaldehyde (Bzal) as products in varying proportions, but with good selectivity for SO. Under optimized conditions, a maximum of 82% selectivity towards SO is obtained at 78% styrene conversion catalyzed by I at room temperature.

Structural diversity and catalytic properties of five Co2(COO)4cluster-based coordination polymers modified with R-isophthalic acid (R = H, NO2, CH3, OH andtBu)

By regulation the substituents on 5-position of isophthalic acid, we isolated five Co-based CPs with structural diversity, which all constructed from the Co2(COO)4unit. The catalytic properties for Knoevenagel condensation and selective epoxidation of styrene have also been investigated.

Thermal oxidative etching method derived graphitic C3N4: highly efficient metal-free catalyst in the selective epoxidation of styrene

A series of g-C3N4 nanosheets were synthesized by thermal oxidation with long time heating and etching.

Highly active Ga promoted Co-HMS-X catalyst towards styrene epoxidation reaction using molecular O2

Atom efficient synthesis of various value added products has been focused as an intense research area after Kyoto protocol. Styrene epoxidation is a challenging reaction as styrene epoxide is an important monomer for large number of polymers. It has been found that surface acidity and redox property of the catalyst has a major contribution to the catalytic activity for oxidation reaction. In this study Co-HMS-X catalyst was prepared and characterized by BET surface area and porosity measurement, SAXS, SANS, FESEM, HRTEM, UV–vis spectra, FTIR, 29Si NMR, H2-TPR and NH3-TPD techniques. It is observed that 5mol% Co-HMS-X showed highest catalytic activity for styrene epoxidation reaction using molecular O2 as an oxidant. Interestingly it is found that among three different dopant (Al, Ga, Tl), the Ga promoted Co-HMS-X catalyst (Si:Co:Ga=100:5:1.25) showed highest catalytic activity in terms of styrene conversion (100%) and styrene epoxide selectivity (68%). The unusual trend of Al, Ga and Tl towards the activity of Co-HMS-X (5mol%) catalyst has been discussed from the results obtained in the H2-TPR and NH3-TPD study.

Epoxidation of Styrene with Molecular Oxygen on Co<sub>3</sub>O<sub>4</sub>/SiO<sub>2</sub> Catalyst

A series of supported catalysts Co3O4/SiO2 were prepared by deposition precipitation method. ICP-AES, XRD and TEM data revealed that the Co3O4 active site was highly dispersed on the surface of SiO2. The catalysts were evaluated for selective epoxidation of styrene with molecular oxygen. The results showed that the catalysts were of good catalytic activity for styrene epoxidation and many factors had an evident effect on the catalytic epoxidation activity. The best catalyst was 3% Co3O4/SiO2 on which 96.3% conversion of styrene and 52.7% selectivity of styrene oxide were obtained under the flow rate of O2 20mL/min, 100°C, 10h with solvent.

Rapid and Highly Selective Epoxidation of Styrene by meta-Chloroperbenzoic Acid Catalyzed by Manganese Meso-tetrakis(Pentafluorophenyl)Porphyrin in the Presence of Tetrabutylammonium Acetate and Bromide

Epoxidation of styrene with m-CPBA in the presence of Mn(TPFPP)Cl was improved to high yield (98–100%) and excellent selectivity (100%) by using n-Bu4NOAc or n-Bu4NBr as co-catalysts in less than 5 min. Also comparison of co-catalytic activity of n-Bu4NOAc, n-Bu4NBr and imidazole in epoxidation of cis-stilbene and styrene was carried out at similar conditions.

Efficient and selective epoxidation of styrene with TBHP catalyzed by Au25clusters on hydroxyapatite

Au(25) clusters supported on hydroxyapatite oxidized styrene in toluene with 100% conversion and 92% selectivity to the epoxide, under optimum conditions and using anhydrous tert-butyl hydroperoxide (TBHP) as an oxidant.

Direct immobilisation versus covalent attachment of a Mn(III) salen complex onto an Al-pillared clay and influence in the catalytic epoxidation of styrene

A Mn(III) salen complex was immobilised onto an aluminium-pillared clay (Al-WYO) by three different methodologies: method A (catalyst A2), direct immobilisation of the complex into the Al-WYO; method B (catalyst A4), covalent anchoring through cyanuric chloride (CC); and method C (catalyst A7), covalent attachment onto a 3-aminopropyltriethoxysilane (APTES) modified Al-WYO mediated by CC. All the materials were characterised by XPS and FTIR; the Mn content of the materials with the immobilised complex was determined by AAS. FTIR and XPS spectra confirmed the organo-functionalisation of Al-WYO and complex immobilisation in the parent and organo-modified Al-PILCs. Direct immobilisation of the complex into the Al-WYO (method A) leads to the highest immobilisation efficiency ( η = 37.5%) compared with the anchoring procedures using the two spacers, methods B and C, which gave η = 7.4% and 8.7%. Nevertheless, the surface Mn contents are always higher than those obtained by bulk analysis, suggesting that in all materials the complexes are located within the most external pores. The Mn(III) salen-based pillared clays were tested in catalytic epoxidation reaction of styrene using iodosylbenzene as the oxygen source and were reused for several cycles. The catalyst A2 was the best heterogeneous catalyst among the catalysts prepared since it showed similar substrate conversion and styrene epoxide selectivity to the homogeneous counterpart; the heterogeneous catalysts A4 and A7 showed considerably lower values for these parameters. The styrene epoxide yields decrease in the order, A2 ≫ A4 > A7, which might be associated with some pernicious catalytic activity of the organo-modified supports (A3 and A6). Moreover, A2 could be reused for four times with a slight decrease in its catalytic activity and with almost no leaching of the active phase.

Selective epoxidation of styrene with air catalyzed by CoOx and CoOx/SiO2 without any reductant

Abstract Cobalt oxide (CoOx) prepared by a direct calcination of cobalt nitrate was considerably active for the epoxidation of styrene with air in DMF under mild conditions. A substrate conversion of 75.8 mol% with an epoxide selectivity of 82.1% was achieved at 353 K over 10 mg of cobalt oxide catalyst. Once CoOx was loaded on the support SiO 2 through a simple procedure consisting of wet impregnation, drying and calcination, the as-prepared catalyst presented higher catalytic activity and epoxide selectivity than cobalt oxide itself. Over the optimized catalyst CoOx/SiO 2 (1.0 wt% Co), 85.7 mol% of styrene was effectively converted at 363 K within 4 h, with a high epoxide selectivity up to 86.0%. The results showed that many factors influenced the performance of the catalyst, such as the Co loading, the support, the temperature and the atmosphere, etc. The leaching of cobalt from the catalyst CoOx/SiO 2 was negligible, indicating the applicability of the catalyst CoOx/SiO 2 as a true heterogeneous catalyst. The control test and UV–vis spectra revealed a synergic interaction among solvent, oxygen and substrate over CoOx/SiO 2 .

Effect of alkali and alkaline earth metal ions on the catalytic epoxidation of styrene with molecular oxygen using cobalt(II)-exchanged zeolite X

Liquid-phase catalytic epoxidation of styrene to styrene epoxide was carried out at 373 K using molecular oxygen at atmospheric pressure, in the presence of Co(II)-exchanged zeolite X. Styrene conversion of >99% with styrene oxide selectivity up to 68% was achieved using NaCoX. Alkali and alkaline earth metal cations were introduced into the zeolite catalyst to increase styrene conversion and styrene oxide selectivity. Replacing the sodium ions with alkali metal cations increased styrene oxide selectivity from 68% for NaCoX19 to 77% for CsCoX20. Styrene oxide selectivity further increased on replacing the sodium ions with alkaline earth metal cations, and styrene oxide selectivity up to 85% and styrene conversion >99% was obtained with CaCoX, SrCoX, and BaCoX. This is the first report of such a high styrene epoxide selectivity with a heterogeneous catalyst observed for styrene epoxidation using molecular oxygen. The presence of a small amount of water in the reaction system increases styrene conversion without affecting styrene oxide selectivity. The cobalt-exchanged zeolite X catalysts showed similar catalytic activity even after three catalytic reaction cycles.

Organo-Laponites as Novel Mesoporous Supports for Manganese(III) salen Catalysts

A Mn(III) salen complex was immobilized onto the Laponite surface using three different methodologies: method A, direct immobilization of the complex on the parent Laponite; method B, covalent anchoring through cyanuric chloride (CC); and method C, covalent anchoring through CC into a 3-aminopropyl)triethoxysilane (APTES) modified Laponite. All of the materials were characterized by FTIR, XPS, thermogravimetry, XRD, and nitrogen isotherms at 77 K, to gather information on the modifications introduced by the organo spacers within the Laponite surface, as well as on the anchored complex integrity; the Mn based materials were screened in the heterogeneous epoxidation of styrene. The results have shown that the immobilization of the manganese(III) salen complex by methods B and C have occurred at the edges of the clay particles through the spacers (APTES and CC) that have been anchored onto the Si-OH groups, whereas in method A, the complex is distributed throughout the clay surface, including the interlayer region. Therefore, the manganese loadings on the Laponites were as follows: materials prepared by method A >> method B > method C. All of the heterogeneous catalysts showed high styrene epoxide selectivity, with that prepared by method A showing comparable styrene epoxide selectivity as the homogeneous phase reaction. The styrene epoxide yields decrease in the following order: materials prepared by method A > method B > method C (1st cycles), which parallel the respective support catalytic activity and decreasing of manganese content. The heterogeneous catalysts prepared using methods B and C could be reused at least for four times, with the former exhibiting the most stable catalytic activity, but that prepared by method A showed a significant decrease after two catalytic cycles.

Mn(III) salen complex immobilised into pillared clays by in situ and simultaneous pillaring/encapsulation procedures : Application in the heterogeneous epoxidation of styrene

The complex [Mn(saldPh)Cl], chloride-[ N, N′-bis(salicylaldehyde)1,2-diphenylethylenediamine]manganese(III), was encapsulated into an aluminium pillared clay (denoted as Al-WYO) by three different methodologies. Method A—two step liquid phase methodology: (i) adsorption of manganese(II) chloride in methanolic solution within an aluminium pillared clay, followed by (ii) diffusion of the ligand N, N′-bis(salicylaldehyde)-1,2-diphenylethylenediamine in methanol. Method B—simultaneous/pillaring encapsulation of the manganese(III) salen complex, [Mn(saldPh)Cl], and pillaring of a montmorillonite clay with aluminium polyoxycations. In this case, the [Mn(saldPh)Cl] complex was dissolved in ethanol and added to the oligomer solution at a stage where the oligomeric species are already formed. Method C—the simultaneous encapsulation also occurred but the complex, also dissolved in ethanol, was added to the clay dispersion. All materials were characterised by XRD, XPS, atomic absorption spectroscopy, UV–Vis, and FTIR. In all cases the manganese(III) salen complex is mainly physically entrapped within the matrix, although some host–guest interactions with the matrix could be present. All new materials, [Mn(saldPh)Cl]@Al-WYO_A, [Mn(saldPh)Cl]@Al-WYO_B, and [Mn(saldPh)Cl]@Al-WYO_C show catalytic activity in the epoxidation of styrene at room temperature using PhIO as oxygen source in acetonitrile. The solids presented high styrene epoxide selectivity and were reused for four times, but a small decrease in the catalytic activity was observed. Nevertheless, the catalysts prepared by simultaneous pillaring/encapsulation, methods B and C, are more stable upon reuse than the catalyst prepared by method A. FTIR spectra of catalysts after the catalytic reactions suggest that during the reaction no structural changes of the PILC took place, but some active phase leaching and deactivation have occurred which are responsible for the decrease in the catalytic activity on reutilisation.

Styrene epoxidation catalysed by manganese(III) salen complex supported on activated carbons

The hydroxyl functionalised manganese(III) salen complex, bearing a large π delocalisation, [Mn(4-HOsaldPh)Cl], was immobilised onto a commercial activated carbon and its air and acid oxidised forms using three different metal loadings. For all the materials the manganese contents were determined by ICP-AES and they were screened as heterogeneous catalysts in the epoxidation of styrene, using iodosylbenzene as oxygen source and acetonitrile as reaction media. All the heterogeneous catalysts were as chemoselective towards the styrene epoxide as the homogeneous counterpart, with the exception of the complex supported onto the acid oxidised activated carbon, which exhibited the lowest styrene epoxide selectivities, a consequence of its acidic oxygen surface groups; the highest styrene conversions and styrene epoxide yields were obtained for that complex immobilised onto the air oxidised activated carbon. Generally, an increase in styrene conversion and styrene epoxide selectivity with the manganese(III) complex loading onto all supports was observed. Upon reuse all the heterogeneous catalysts do not lose their styrene epoxide selectivity, but generally a slight decrease in the styrene epoxide yield is observed; catalyst aging studies done for one of the material prepared, [Mn(4-OHsaldPh)Cl]@C2_1%, revealed high stability and the same catalytic efficiency for almost 2 months.

Catalytic Properties of a MnIII‐Salen Complex Immobilised in a Pillared Clay by Simultaneous Pillaring/Encapsulation Procedures

AbstractThe simultaneous encapsulation of a manganese(III)‐salen complex, [Mn(salhd)Cl], and pillaring of a montmorillonite clay with aluminium polyoxycations was performed using two methods: method A – the [Mn(salhd)Cl] complex was dissolved in ethanol and added to the oligomer solution at a stage when the oligomeric species had already formed; method B – the complex, also dissolved in ethanol, was added to the clay dispersion. After calcination, both materials were Soxhlet extracted to remove the excess complex, and characterised by XRD, nitrogen adsorption at –196 °C, XPS, atomic absorption and FTIR spectroscopy. In both cases, the manganese(III)‐salen complex is mainly physically entrapped within the matrix, although some host–guest interactions with the matrix may be present. Both new materials [Mn(salhd)Cl]@Al‐WYO_A and [Mn(salhd)Cl]@Al‐WYO_B show catalytic activity in the epoxidation of styrene at room temperature with PhIO as oxygen source in acetonitrile. The solids present high styrene epoxide selectivity, and may be reused at least four times. FTIR spectra of the catalysts after the catalytic reactions suggest that during the reaction no structural changes of the pillared clay (PILC) took place, but low extent complex leaching occurred. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Epoxidation of styrene with hydrogen peroxide using hydrotalcites as heterogeneous catalysts

Several Mg/Al hydrotalcite-like materials with atomic ratios of 2, 3, 4, 6 and 10 were tested as heterogeneous catalysts for the epoxidation reaction of styrene, using a combined oxidant of hydrogen peroxide and acetonitrile in the presence of acetone and water as solvents. Several factors such as the Mg/Al ratio, the presence of the pure hydrotalcite phase in the samples, the reconstruction rate of the hydrotalcite-like phase, carried out during the reaction, and the addition of water, play an important role in the selective epoxidation of styrene. Several characterization techniques such as inductivity coupled plasma (ICP), powder XRD, TGA, IR spectra, SEM, 27Al NMR spectra, TPD of CO 2 and N 2 physisorption were performed in order to correlate the chemical and textural properties of the as-synthesized and calcined materials with their catalytic behaviors.

Biphasic selective epoxidation of styrene by t-butyl hydroperoxide to styrene oxide using potassium chromate or dichromate catalyst in aqueous medium

Styrene oxide with high selectivity (>60%) at high conversion (>50%) can be produced in the biphasic epoxidation of styrene by t-butyl hydroperoxide, using easily separable potassium chromate or dichromate as catalyst in the presence of water; the reactants and products exist in the non-aqueous (organic) phase, while the catalyst exists in the aqueous phase. Both potassium chromate and dichromate catalysts show very high activity in the biphasic epoxidation; however, a more preferable catalyst is potassium chromate.

Photocatalytic selective epoxidation of styrene by molecular oxygen over highly dispersed titanium dioxide species on silica

Photocatalytic selective epoxidation of styrene by molecular oxygen over highly dispersed titanium dioxide species on silica