Catalysts For Epoxidation Of Styrene Research Articles

Enantioselective Epoxidation of Styrene by Manganese Chiral Schiff Base Complexes Immobilized on MCM-41.

Two chiral MnIII complexes synthesized and characterized by single-crystal X-ray diffraction were grafted onto mesoporous silica MCM-41. The MCM-41-immobilized solid chiral catalysts were characterized by various spectrochemical and physicochemical methods (XRD, FTIR, 29 Si NMR, TGA, UV/Vis/DRS, EPR, cyclic voltammetry, SEM, BET). Both the homogeneous and heterogeneous MnIII chiral complexes are found to be effective catalysts for epoxidation of styrene. MCM-41-supported chiral catalysts are found to retain their catalytic activity up to five cycles. When an ionic liquid was implemented to enhance the catalytic recyclability of the homogeneous catalysts, they can be recycled up to three times. However, after the third cycle the catalytic activities of the complexes were found to decrease due to rupturing of the chiral catalyst.

Prussian blue analogues as heterogeneous catalysts for epoxidation of styrene

Prussian blue analogues are high performance catalyst for low toxicity, lower dosage reactions, simple preparation processes and cheap.

Catalytic Performance of Cobalt-Schiff Base-Chitosan/attapulgite for Epoxidation of Styrene

With the Schiff base of L-aspartic acid and salicylaldehyde as the ligands,the composite resin of chitosan/attapulgite(CS/ATP) produced by NaOH curing method as the carrier,the Schiff base metal complexes and the load-type Schiff base metal complexes of Co,Mn,Cu,Fe,Ni were synthesized.Their structural characterizations were determined by FT-IR.The catalytic performance of each catalyst for epoxidation of styrene was studied.Experiments show that the catalytic performance of Co-Schiff base is better in small molecule ligand Schiff base metal complexes.Therefore,Co-Schiff base was loaded in CS/ATP composite resin and the effects of the amount of Co-Schiff base-CS/ATP catalyst,reaction temperature and reaction time on the catalytic epoxidation of styrene were investigated.Finally the results show that the best reaction conditions are as follows:the temperature is 80 ℃ and the reaction time is 8 h,which results in a conversion rate of 93.1% for epoxidation of styrene.

Immobilization of transition metal (Fe2+, Co2+, VO2+ or Cu2+) Schiff base complexes onto graphene oxide as efficient and recyclable catalysts for epoxidation of styrene

Transition metal (Fe2+, Co2+, VO2+ or Cu2+) Schiff base complexes were immobilized onto graphene oxide previously functionalized with 3-aminopropyltriethoxysilane (3-APTES). X-ray diffraction (XRD), IR spectroscopy, thermal gravimetric analyses (TGA) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) confirmed the successful incorporation of the metal Schiff base onto the graphene oxide. N2 adsorption–desorption, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) showed the intact structure of the graphene oxide. Catalytic results showed that the immobilized copper(II) Schiff base complex catalyst was more active than the immobilized iron(II), cobalt(II) and oxovanadium(IV) complexes in the epooxidation of styrene. Above 94% styrene conversion and excellent ∼99% selectivity to the epoxide could be achieved over the copper(II) Schiff base heterogeneous catalyst in the epoxidation of styrene using tert-butyl hydroperoxide (TBHP) as oxidant after 7 h reaction. The recycling experiment results indicated that the catalyst could maintain very high styrene conversion (>93%) and epoxide selectivity (>99%) even after being used for four cycles.

Biosynthesized gold nanoparticles supported over TS-1 toward efficient catalyst for epoxidation of styrene

Au/TS-1 catalysts prepared by an eco-friendly and economical bioreduction method were used for the liquid phase epoxidation of styrene to styrene oxide (SO) using aqueous hydrogen peroxide (H2O2) as oxidant. The catalysts were characterized by a variety of techniques including FT-IR, DRUV–Vis, UV–Vis, N2 physisorption, XRD, XPS, TG–DTG and TEM. The influence of various parameters (Au loading, calcination, solvents, oxidants, reaction temperature, reaction time and catalyst amount) on the catalytic performance was systematically investigated. The results showed that both the conversion of styrene and selectivity to SO were improved and enhanced when catalyzed by biosynthesized gold nanoparticles (GNPs) supported on TS-1. However, decomposing the Cacumen Platycladi (CP) biomass properly through calcinations can enhance the catalytic performance though it acted as reductant and protective agents during the catalysts preparation. Besides, the optimum catalytic activity and stability of bioreduction Au/TS-1 catalysts were obtained under operational conditions of Au loading of 1.0wt.%, CP extract (10gL−1) as reductant, calcined at 723K for 2h, reaction time of 10h, reaction temperature of 333K, catalyst amount of 500mg, aqueous H2O2 (30wt.%) as oxidant and N,N-dimethylformamide as solvent. Under the optimal condition, styrene conversion of 92.7% and SO selectivity of 90.4% was achieved, which were comparable or even superior to those reported in the literatures. The catalyst was reused five times, without significant decrease in both the styrene conversion and SO selectivity.

Enhanced catalytic performances of Ag nanoparticles supported on layered double hydroxide for styrene epoxidation

Catalysts or support to catalysts based on layered double hydroxides (LDHs) have been widely investigated in the last few years. Supported Au nanoparticles (NPs), prepared typically by a homogeneous deposition–precipitation technique, have been utilized as catalysts with high activity and selectivity for styrene epoxidation. We herein present a preparation of chemically reduced and cost-saving Ag NPs on the LDH support used as catalyst for styrene epoxidation. A proper reaction condition is optimized, for example, a loading of 2.67 wt% Ag, a conversion temperature of 82 °C, and a conversion time of 8 h. The Ag/LDH catalyst exhibits enhanced reaction selectivity and product yield in comparison with the Au/LDH reported previously. Our results may initiate a facile framework appropriate for noble metallic NPs supported on layered inorganic crystal compounds.

Anatase type extra-framework titanium in TS-1: A vital factor influencing the catalytic activity toward styrene epoxidation

Anatase type extra-framework titanium in titanium silicate-1 (TS-1) molecular sieves has been observed to cause adverse catalytic impediments such as carbon–carbon bond cleavage and low H2O2 efficiency during the epoxidation of terminal alkenes. In this study, a series of TS-1 sieves were synthesized, and used as catalysts for styrene epoxidation. Among the catalysts, the TS-1 with a Si/Ti molar ratio of 35 and 0.21mol% of anatase type extra-framework titanium exhibited the best styrene conversion and styrene oxide (SO) selectivity. The results suggests that, framework Ti species have no effect on the stabilization of SO selectivity, whereas the synergetic interaction between the framework Ti species and the anatase type extra-framework titanium is essential for the outstanding catalytic performance of TS-1 in styrene epoxidation. In addition, our results demonstrate that the usage of tetraethyl orthosilicate (TEOS), tetrabutyl titanate (TBOT), and isopropyl alcohol in the synthesis of TS-1 does not guarantee the absence of extra-framework Ti species. Instead, the asynchronous degrees of hydrolysis between TEOS and TBOT might account for the formation of the anatase type extra-framework titanium. The influence of H2O2 amount, reaction temperature and time, as well as the types of solvent, oxidant, and catalyst amount, on the catalytic performance of TS-1 with anatase type extra-framework titanium was likewise investigated.

Crystal structure of an unsymmetrical Schiff base, immobilization of its cobalt and manganese complexes on a silica support, and catalytic studies

An unsymmetrical tetradentate Schiff base (H2L) was synthesized by the reaction of 3-methoxysalicylaldehyde, o-phenylenediamine, and salicylaldehyde in EtOH. H2L was characterized by single-crystallographic X-ray analysis. Its Co(II) and Mn(III) complexes ([CoL] and [MnLCl]) were prepared and immobilized on 3-aminopropyltriethoxysilane functionalized silica gel. The immobilized materials were found to be efficient catalysts for epoxidation of styrene in the presence of tert-BuOOH in acetonitrile at 40 °C. The catalysts can be reused several times without significant loss of performance.

Vanadium complexes with quadridentate Schiff bases

The Schiff base ligands N,N′-(±)-trans-bis(3,5-dichloro-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H2L1) and N,N′-(±)-trans-bis(5-chloro-4-methyl-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H2L2) were derived from the condensation of trans-1,2-diaminocyclohexane with 3,5-dichloro-2-hydroxyacetophenone or 5-chloro-4-methyl-2-hydroxyacetophenone, respectively. Both these ligands formed well-defined complexes with vanadium (IV) and (V) under suitable experimental conditions. These complexes have been characterized by elemental analysis, molar conductivity, magnetic moments, infrared, electronic spectra, ESR, X-ray diffraction, and thermogravimetric analysis. X-ray diffraction study of [VO(L2)]·H2O complex indicated its monoclinic crystal system with a = 9.8525, b = 23.6271, c = 9.0904 A, and β = 97.87°. The complexes [VO(L1)]·H2O and [VO(L2)]·H2O have been examined as catalysts for epoxidation of styrene in the presence of hydrogen peroxide as oxidant. The IR spectral data suggest that both the ligands behave as dibasic tetradentate chelating agent with ONNO donor atoms sequence toward cental metal ion.

Ag‐Cu Bimetallic Nanoparticles Prepared by Microemulsion Method as Catalyst for Epoxidation of Styrene

Ag/Cu bimetallic nanocatalysts supported on reticulate‐like γ‐alumina were prepared by a microemulsion method using N2H4·H2O as the reducing agent. The catalysts were activated by calcination followed with hydrogen reduction at 873K, and the properties were confirmed using various characterization techniques. Compared with metal oxides particles, Ag‐Cu particles exhibited smaller sizes (<5 nm) after calcination in H2 at 873K. XPS results indicated that the binding energies changed with the Ag/Cu ratios, suggesting that increasing the copper content gave both metals a greater tendency to lose electrons. Furthermore, Ag‐Cu bimetallic nanoparticles supported on γ‐alumina showed better catalytic activity on the epoxidation of styrene as compared with the corresponding monometallic silver or copper. The styrene oxide selectivity could reach 76.6% at Ag/Cu molar ratio of 3/1, while the maximum conversion (up to 94.6%) appeared at Ag/Cu molar ratio of 1/1 because of the maximum interaction between silver and copper.

Crystal-Face-Selective Supporting of Gold Nanoparticles on Layered Double Hydroxide as Efficient Catalyst for Epoxidation of Styrene

Au catalysts with layered double hydroxide (LDH) as support were fabricated and the crystal faces feature of LDH platelets was revealed to have a crucial effect on the location and particle size of gold nanoparticles (AuNPs). A preferential deposition of AuNPs with a narrow size distribution was formed on the lateral {101̅0} faces of LDH platelets. Catalytic property evaluation of the resulting Au/LDH samples showed that the conversion of styrene with tert-butyl hydroperoxide (TBHP) to styrene oxide (SO) occurred on the AuNPs with particle size of 2−3 nm, mainly deposited on the lateral faces of LDH support.

Transition metal complexes on mesoporous silica nanoparticles as highly efficient catalysts for epoxidation of styrene

We have synthesized a series of catalysts for epoxidation of styrene by immobilizing salicylaldimine transition metal (copper, manganese, and cobalt) complexes on mesoporous silica nanoparticles (MSNs) with diameters of 120–150 nm. The prepared catalysts are characterized by infrared (IR) spectra, thermal gravimetric analyses (TGA), inductively coupled plasma (ICP), CHN elemental analysis, nitrogen adsorption–desorption, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). These catalysts possess excellent catalytic efficiency in epoxidation of styrene when using tert-BuOOH (TBHP) as oxidant. Styrene shows a high conversion (∼99%) as well as epoxide selectivity (∼80%) over Cu-MSN catalysts, and high conversion (∼99%) and moderate epoxide selectivity (∼65%) over Mn-MSN and Co-MSN catalysts. The recycling experiment results indicate that these catalysts maintain catalytic activity even after being used for three cycles. Our results indicate that MSNs can serve as better catalyst supports.

Adsorption synthesized cobalt-containing mesoporous silica SBA-15 as highly active catalysts for epoxidation of styrene with molecular oxygen

Co2+ was introduced into aminopropyl-functionalized mesoporous silica SBA-15 by an adsorption method. Characterizations with XRD and HRTEM suggested that the prepared material still retained a highly ordered structure, and the cobalt ions were highly dispersed in the molecular sieves. The cobalt-containing SBA-15 was considerably active in the epoxidation of styrene with O2. Cobalt content, preparation method and oxidant influenced the catalytic performance. The material possessed better stability and recyclability in the reaction.

Co-SSZ-51 as a catalyst for styrene epoxidation using molecular oxygen

Cobalt substituted SSZ-51 molecular sieve (Co/P molar ratio = 0/0.01/0.05/0.1) samples are synthesized by isomorphic substitution as well as wet impregnation with cobalt salt. The prepared samples are characterized for of their textural and structural properties. The catalytic potential of these samples is investigated for styrene epoxidation in the presence of molecular oxygen at 60 psi. The obtained results showed styrene conversion up to ∼50% with 70–80% selectivity for styrene epoxide till three reaction cycles using Co-substituted SSZ-51 framework. On the other hand cobalt impregnated SSZ-51 samples showed poor selectivity for epoxide (up to 40% only). The obtained results are discussed in terms of cobalt oxidation state present in SSZ-51 framework.

Enhanced catalytic performances by surface silylation of Cu(II) Schiff base-containing SBA-15 in epoxidation of styrene with H 2O 2

Schiff base functionalized SBA-15 mesoporous materials were synthesized by post-grafting of salicylaldehyde onto silylated and non-silylated amino-modified SBA-15 and followed by the introduction of Cu(II) ions via a ligand exchange reaction. Both hybrid materials prepared were characterized by XRD, FT-IR, UV–vis spectroscopy, N 2 adsorption/desorption, TG/DTA and ICP-AES techniques and comparatively examined as catalysts in epoxidation of styrene with 30 wt.% aqueous hydrogen peroxide as oxidant. It was found that the silylated material was more active and selective to styrene oxide than the non-silylated one in CH 3CN. The considerably improved activity (86.1%) and styrene oxide selectivity (95.2%) were achieved after 30 min when adding sodium hydroxide to maintain a pH of 7.5–8.0 in reaction medium. Moreover, the silylated catalyst showed good recoverability and relatively high stability against leaching of active copper species. These superior effects were attributed to the high hydrophobic character of the solid surface produced by the silanol neutralization.

Microwave Synthesized Mesoporous Vanadium-MFI Catalysts for Epoxidation of Styrene Using Molecular Oxygen

Carbon templated mesoporous vanadium MFI catalysts with different Si/V ratios were successfully synthesized using microwave irradiation. X-ray diffraction studies revealed the formation of more crystalline MFI structures. SEM and TEM imaging also showed well ordered zeolite single crystals having mesoporosity. The N2 sorption isotherm showed the formation of bimodal mesoporous zeolites. FT-IR studies showed absorbance around 970 cm−1 corresponding to Si–O–V stretching vibration and the UV–Vis studies revealed strong peaks in the range of 230–340 nm which is related to the presence of tetrahedral V5+ state. The catalytic activity of the microwave synthesized catalysts was evaluated for epoxidation of styrene using molecular oxygen. The catalysts exhibited 20–40% styrene conversion with 60–75% epoxide selectivity. With increasing Vanadium content, the conversion as well as the selectivity was observed to increase. The catalyst could be recycled for three cycles without a loss in activity.

Copper-containing hexagonal mesoporous silicas for styrene epoxidation using tert-butylhydroperoxide

Copper-containing hexagonal mesoporous silicas (Cu-HMS) with different Si/Cu atomic ratios were synthesized by one-pot sol–gel method using dodecylamine surfactant as templating agent. The structure was characterized by X-ray diffraction, N 2 adsorption–desorption, infrared spectroscopy, transmission electron microscopy, ultraviolet and visible diffuse reflectance spectroscopy, electron spin resonance and H 2 temperature-programmed reduction. The results show that the Cu-HMS material is an efficient catalyst for epoxidation of styrene with use of aqueous tert-butylhydroperoxide. The catalytic performance is dependent on Si/Cu atomic ratio and reaction solvent. A styrene conversion of 99% with epoxide selectivity up to 84% can be obtained over the Cu-HMS material with Si/Cu atomic ratio of 40 in the case of using a mixed solvent of acetonitrile and N, N-dimethylformamide. No significant loss in the catalytic performance is observed during catalyst reuse. The enhanced catalytic performance over Cu-HMS material may be attributed to the homogeneous dispersion and uniformity of active Cu 2+ species.

Supported Nano-Gold Catalysts for Epoxidation of Styrene and Oxidation of Benzyl Alcohol to Benzaldehyde

Nano-gold particles supported on different alkaline earth oxides (viz. MgO, CaO, BaO and SrO), Gr. IIIa metal oxides (viz. Al2O3, Ga2O3, In2O3 and Tl2O3), transition metal oxides (viz. TiO2, Cr2O3, MnO2, Fe2O3, CoOx, NiO, CuO, ZnO, Y2O3 and ZrO2), rare earth metal oxides (viz. La2O3, Ce2O3, Nd2O3, Sm2O3, Eu2O3, Tb2O3, Er2O3 and Yb2O3) and U3O8 [all prepared by depositing gold on corresponding metal oxide support by deposition precipitation (DP) and/or homogeneous deposition precipitation (HDP) method] were evaluated for their catalytic performance in the liquid phase epoxidation of styrene by tert-butyl hydroperoxide (TBHP) to styrene oxide and also in the solvent-free benzyl alcohol-to-benzaldehyde oxidation (by molecular oxygen or TBHP) reactions. For the epoxidation, the catalytic performance (styrene oxide yield) of the most promising nano-gold catalysts prepared by the HDP method was in the following order: Au/MgO > Au/Tl2O3 > Au/Yb2O3 > Au/Tb2O3 > Au/CaO (or TiO2). However, for the oxidation of benzyl alcohol to benzaldehyde by molecular oxygen, the order of choice for the most promising catalysts (based on benzaldehyde yield) was Au/U3O8 > Au/Al2O3 > Au/ZrO2 > Au/MgO. Whereas, when TBHP was used as an oxidizing agent for the benzyl alcohol oxidation, the order of choice for the most promising catalysts was Au/U3O8 > Au/MgO > Au/TiO2 > Au/ZrO2 > Au/Al2O3. The catalytic performance of a particular supported nano-gold catalyst was thus found to depend on the reaction catalysed by them. Moreover, it is strongly influenced by a number of catalyst parameters, such as the metal oxide support, the method of gold depositon on the support, the gold loading and also on the catalyst calcination temperature. Nano-gold particles-support interactions seem to play an important role in controlling the deposition of gold (amount of gold deposited and size and morphology of gold particles), formation of different surface gold species (Au0, Au1+ and Au3+) and electronic properties of gold particles and, consequently, control the catalytic performance (both the activity and selectivity) of the supported nano-gold catalysts in the reactions. The nano-gold catalysts prepared by the HDP method showed much better catalytic performance than those prepared by the DP, coprecipitation or impregnation method; in general, the HDP method provided supported gold catalysts with much higher gold loading and/or smaller size gold particles than that achieved by the DP and other methods.

Zirconium phosphonates-supported chiral Mn (III) Salen complexes for the asymmetric epoxidation of unfunctionalized olefins

Abstract The mesoporous zirconium phosphonates-supported Mn (III) Salen complexes ( 1a–e ) with the different lengths of alkylsulfonic linkage ( n = 2–6) and the loading amount of 0.041–0.059 mmol g −1 (based on Mn) were prepared and used as heterogeneous catalysts in the asymmetric epoxidation of styrene, α-methylstyrene and indene. The ee values significantly increased with the linkage length ( n ) from 2 to 6 only in the case of indene with the m- CPBA/NMO as an oxidant system, in all other shown cases the ee values are not significantly influenced by the linkage length ( n ). In m -CPBA/NMO system, the comparable ee values to the homogeneous Mn (III) Salen complex 1 were achieved. Due to the confined effect originating from the nanopores of zirconium phosphonates, the heterogeneous Mn (III) Salen complexes ( 1a–e ) gave twice (84–88%ee) as many as ee values of homogeneous Mn (III) Salen complex 1 (49%ee) in the NaClO/PPNO system.

Ti-MCM-41 supported phosphotungstic acid: An effective and environmentally benign catalyst for epoxidation of styrene

Mesoporous Ti-MCM-41 molecular sieve was synthesized under hydrothermal conditions. 5, 10, 20, 30 and 50 wt.% phosphotungstic acid (H 3PW 12O 40) (PW) were supported on Ti-MCM-41 and the resulting catalysts were characterized by powder X-ray diffraction (XRD), N 2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), UV–vis diffuse reflectance spectroscopy (DRS), thermogravimetric analysis (TGA) and differential thermal analysis (DTA), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and high-resolution transmission electron microscopy (HRTEM). The host material suffers severe structural distortions at higher loading, which lead to a considerable loss of long-range orders. Their catalytic performances were evaluated in the epoxidation of styrene with dilute H 2O 2 (30%) as an oxidizing agent under liquid-phase reaction conditions over PW/Ti-MCM-41 catalysts for selective synthesis of styrene oxide. The influences of various reaction parameters such as temperature, time, solvents, PW loading and catalyst amount, styrene to H 2O 2 mmol ratios and acetonitrile (MeCN) to N, N-dimethylformamide (DMF) volume ratios on the conversion of styrene and yield as well as selectivity of styrene oxide have also been studied in details. The results revealed that 20% PW/Ti-MCM-41 was more active than other catalysts. The PW/Ti-MCM-41, moreover, was found to be reusable and effective for the epoxidation of styrene.