Selective Oxidation Of Styrene Research Articles

Selective oxidation of styrene on an oxygen‐adsorbed Cu(111): A comparison with Au(111)

The reaction mechanism for the styrene selective oxidation on the oxygen preadsorbed Cu(111) surface has been studied by the density functional theory calculation with the periodic slab model. The calculated result indicated that the process includes two steps: forming the oxametallacycle intermediate (OMMS) and then producing the products. In addition, it was found that the second step, from OMMS to the product, is the rate-controlling step, which is similar to the previous work of ethylene selective oxidation. The present result indicated that the selectivity towards the formation of styrene epoxide on Cu(111) is much higher than that on Au(111). More importantly, we found that the mechanism via the OMMS (2) (i.e., the preadsorbed atomic oxygen bound to the CH(2) group involved in C(6)H(5)-CH=CH(2)) to produce styrene epoxide is kinetically favored than that of OMMS (1). We also found that the selectivity toward the styrene epoxide formation on Cu(2)O is similar to that of Cu(111).

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-assisted epoxidation of styrene with molecular O2 over sulfated Co–Y–ZrO2 solid catalyst

Abstract The microwave-assisted styrene epoxidation reaction with molecular O 2 as an oxidant was studied over a sulfated Co–Y-doped ZrO 2 solid catalyst. The microwave irradiation (400 W) resulted in similar styrene conversion and styrene oxide selectivity, in reduced time, as compared to conventional thermal heating. Higher power (800 W) of microwave irradiation decreased the styrene oxide selectivity as well as leading to the formation of styrene glycol. DMF was found to be the most suitable solvent for epoxidation of styrene with molecular O 2 under microwave irradiation and yielded maximum oxide selectivity (91%) at 120 °C. The microwave-assisted oxidation reaction resulted in time saving and is energy conserving method.

Selective oxidation of styrene to benzaldehyde catalyzed by Schiff base-modified ordered mesoporous silica materials impregnated with the transition metal-monosubstituted Keggin-type polyoxometalates

A series of Schiff base-modified ordered mesoporous silica materials impregnated with the transition metal-monosubstituted Keggin-type polyoxometalates (mono-TMSPs), K 10− n X n+ MW 11O 39-Schiff-SBA-15, (X = P/Si, M = Co/Ni/Cu/Mn), was prepared using successive grafting procedures of SBA-15 silica with 3-aminopropyl-trimethoxysilane, benzaldehyde, and mono-TMSP. The composite materials were well-characterized by spectroscopy methods, X-ray diffraction analysis, transmission electron microscopy, and nitrogen sorption analysis to confirm the structure integrities of the Keggin unit and Schiff base ligand after the incorporation, to evidence formation of the coordination binding between the starting Keggin units and the Schiff base-modified silica matrix, and to investigate the morphology and surface textural properties of the composite catalysts. These materials were subsequently utilized as efficient and selective catalysts in the reaction of oxidation of styrene to benzaldehyde using H 2O 2 as an oxidant. For comparison, an amine-modified SBA-15 silica material impregnated with mono-TMSP (K 10− n X n+ MW 11O 39-NH 2-SBA-15) and the neat Keggin unit (K 10− n [X n+ M(H 2O)W 11O 39]) was also tested. The influences of key reaction parameters, including the molar ratios of H 2O 2 to styrene, compositions and loadings of the neat mono-TMSPs, solvents, the catalyst amount, and reaction temperatures on the reactivity and selectivity, were also studied. Finally, the reusability of the catalysts was evaluated.

Monometallic and heterobimetallic complexes derived from salen-type ligands

Abstract Mononuclear and heterodinuclear complexes of the salen-type ligand H2LH2 [H2LH2 = 2,2′-[1,2-dihydroxybenzene-4,5-diylbis(nitrilomethylidine)]bis(3,5-di-tert-butylphenol)] were prepared, whereof [{Mn(CH3OH)2}LH2]Cl, [ML( ZrCp 2 ∗ )] (M = Ni, Cu, CrCl(py); py = pyridine, Cp∗ = pentamethylcyclopentadienyl) were characterized by X-ray analysis. Additionally, cyclic voltammetric investigations were performed to ascertain the influence of the second transition metal complex fragment [ ZrCp 2 ∗ ]2+ on the metallo salen ligand. Moreover, the complexes were tested in the catalytic epoxidation of styrene. Although the complexes are quite sensitive towards oxidants, monometallic complex [{Mn(CH3OH)2}LH2]Cl exhibited a conversion of 70.6% with styrene oxide selectivity of 88% over 1 h at room temperature.

Synthesis and characterization of Cr-MSU-1 and its catalytic application for oxidation of styrene

Chromium-containing mesoporous silica material Cr-MSU-1 was synthesized using lauryl alcohol–polyoxyethylene (23) ether as templating agent under the neutral pH condition by two-step method. The sample was characterized by XRD, TEM, FT-IR, UV–Vis, ESR, ICP-AES and N 2 adsorption. Its catalytic performance for oxidation of styrene was studied. Effects of the solvent used, the styrene/H 2O 2 mole ratio and the reaction temperature and time on the oxidation of styrene over the Cr-MSU-1 catalyst were examined. The results indicate that Cr ions have been successfully incorporated into the framework of MSU-1 and the Cr-MSU-1 material has a uniform worm-like holes mesoporous structure. After Cr-MSU-1 is calcined, most of Cr 3+ is oxidized to Cr 5+ and Cr 6+ in tetrahedral coordination and no extra-framework Cr 2O 3 is formed. The Cr-MSU-1 catalyst is highly active for the selective oxidation of styrene and the main reaction products over Cr-MSU-1 are benzaldehyde and phenylacetaldehyde. Its catalytic performance remains stable within five repeated runs and no leaching is noticed for this chromium-based catalyst.

Selective Oxidation of Styrene in Ionic Liquid and its Reaction Kinetics

Selective oxidation of styrene to benzaldehyde by molecular oxygen was investigated, while the brönsted ionic liquid was used as solvent, and the Mn(III)-salen complex as the catalyst, the products obtained were detected by GC. The best process conditions were [Bmim]PF 6 to be the solvent and T = 343K, P = 0.5MPa with 0.1% (n/n) catalysts. Furthermore, the dynamic model was established and relevant parameters were acquired through the mathematical deduction and experimental data analysis. For this system, the reaction dynamical equation for the oxidation of styrene was expressed as following: with the Ea of the oxidation was 111.99 kJ/mol.

Highly selective synthesis of styrene oxide over phosphotungstic acid supported on mesoporous Mn-MCM-41 molecular sieves

Tungstophosphoric acid (H3PW12O40) (PW) catalysts supported on mesoporous Mn-MCM-41(n Si/n Mn = 25) with various (10, 20 and 30 wt%) acid loadings were prepared by impregnation, and their physical chemical properties were characterized by powder X-ray diffraction (XRD), N2 adsorption–desorption, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), high resolution transmission electron microscopy (HRTEM), and X-Ray Photoelectron Spectroscopy (XPS). 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 H2O2 (30%) as an oxidizing agent under liquid phase reaction conditions over PW/Mn-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 H2O2 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/Mn-MCM-41 (n Si/n Mn = 25) was more active than other catalysts. The PW/Mn-MCM-41, moreover, was found to be reusable and environmentally benign for the epoxidation of styrene.

Styrene oxidation with H2O2 over Fe- and Ti-SBA-1 mesoporous silica

The catalytic activity of M-SBA-1 (M = Fe and Ti), synthesized using silatrane as the precursor, was studied in the liquid phase oxidation of styrene using hydrogen peroxide as the oxidant. The influence of time-on-stream, affecting the catalytic activity and the selectivity of styrene, was studied. At 80 °C, the selectivity for benzaldehyde and styrene oxide reached 74% and 11%, respectively, at a styrene conversion of 67 ± 1.49% over 4 wt% Fe in SBA-1, while that for benzaldehyde and styrene oxide reached 50% and 48%, respectively, at a styrene conversion of 69 ± 2.20% over 2 wt% Ti in SBA-1.

Selective aerobic oxidation of styrene to benzaldehyde catalyzed by water-soluble palladium(II) complex in water

Selective oxidation of styrene to benzaldehyde has been carried out for the first time in aqueous phase by using a green and water-soluble palladium(II) complex as a catalyst under neutral, chloride and base-free conditions. The influences of reaction temperature, reaction time, palladium concentration and O2 pressure on the conversion of styrene and the selectivity to benzaldehyde have been discussed. The reaction products, benzaldehyde, benzoic acid, acetophenone are readily isolated by ether extraction at room temperature. The water-soluble catalyst immobilized in aqueous phase can be reused for eight catalytic runs with an almost constant catalytic activity for the styrene oxidation. The influence of substituting groups in the aromatic ring of styrene on the reactivity was also discussed. Spectroscopic studies revealed that the hydrophilic dipyridyl-based ligand (L) with Pd(OAc)2 formed a water-soluble Pd(II) complex. The UV/Vis spectra analysis further showed that the Pd(II)-L complex could serve as the catalytically active species in the present catalytic system.

Epoxidation of Styrene with Hydrogen Peroxide over Mn-Ti-Al-MCM-41 Molecular Sieve under Microwave Irradiation

Abstract Mesoporous molecular sieves Mn-Ti-Al-MCM-41 prepared by in situ microwave hydrothermal synthesis were studied for the epoxidation of styrene with H 2 O 2 under microwave irradiation. Characterization by XRD, 29 Si MAS NMR, N 2 physisorption, SEM-EDS, and HRTEM revealed that the materials had a typical hexagonally arranged mesoporous structure with high surface area and narrow pore size distribution. The novel synthesis method of Mn-Ti-Al-MCM-41 shortened the synthesis time from days to hours, and the as-synthesized materials had a higher catalytic activity in the liquid-phase epoxidation of styrene and greatly improved the selectivity for styrene oxide.

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.

Selective oxidation of styrene on an oxygen‐adsorbed Au(111): A density functional theory study

The reaction mechanism for the styrene selective oxidation on the oxygen preadsorbed Au(111) surface has been studied by the density functional theory calculation with the periodic slab model. The calculated results showed that the process of reaction includes two steps: forming the oxametallacycle intermediate (OMME) and then producing the products. It was found that the second step, from OMME to product is the rate-controlling step, which is similar to ethylene selective oxidation on Ag. Importantly, the present density-functional-theory calculation results suggested that the mechanism via the OMME (2) (i.e. the preadsorbed atomic oxygen bound to the CH2 group involved in C6H5--CH=CH2) to produce styrene epoxide is kinetically favored than that of OMME (1).

Selective oxidation with dioxygen by gold nanoparticle catalysts derived from 55-atom clusters

Supported gold nanoparticles have excited much interest owing to their unusual and somewhat unexpected catalytic properties, but the origin of the catalytic activity is still not fully understood. Experimental work on gold particles supported on a titanium dioxide (110) single-crystal surface has established a striking size threshold effect associated with a metal-to-insulator transition, with gold particles catalytically active only if their diameters fall below approximately 3.5 nm. However, the remarkable catalytic behaviour might also in part arise from strong electronic interaction between the gold and the titanium dioxide support. In the case of industrially important selective oxidation reactions, explanation of the effectiveness of gold nanoparticle catalysts is complicated by the need for additives to drive the reaction, and/or the presence of strong support interactions and incomplete understanding of their possible catalytic role. Here we show that very small gold entities ( approximately 1.4 nm) derived from 55-atom gold clusters and supported on inert materials are efficient and robust catalysts for the selective oxidation of styrene by dioxygen. We find a sharp size threshold in catalytic activity, in that particles with diameters of approximately 2 nm and above are completely inactive. Our observations suggest that catalytic activity arises from the altered electronic structure intrinsic to small gold nanoparticles, and that the use of 55-atom gold clusters may prove a viable route to the synthesis of robust gold catalysts suited to practical application.

Preparation of periodic mesoporous silica-included divacant Keggin units for the catalytic oxidation of styrene to synthesize styrene oxide

Periodic mesoporous composite catalysts, [( n-C 4H 9) 4N] 4[γ-SiW 10O 34(H 2O) 2]/SBA-15 (TBA-1*/SBA-15, where TBA-1* = [( n-C 4H 9) 4N] 4[γ-SiW 10O 34(H 2O) 2]), with TBA-1* loadings of 4.3–14.8% were prepared by simultaneous hydrolysis and co-condensation of the tetraethoxysilane (TEOS) in the presence of divacant Keggin-type polyoxometalate and triblock copolymer surfactant (P123) followed by hydrothermal treatment process. Structure integrity of the Keggin unit in as-prepared composites was studied by Fourier transform infrared spectroscopy (FT-IR), Raman scattering spectra, and 29Si magic-angle spinning (MAS) NMR. Periodic mesoporous structure of the composites was evaluated by low-angle X-ray powder diffraction (LXRD) patterns, nitrogen porosimetry, and transmission electron microscope (TEM) measurements. As-prepared TBA-1*/SBA-15 was used as an heterogeneous oxidation catalyst for the styrene epoxidation reaction to synthesize styrene oxide in the presence of dilute H 2O 2 (30%), and influences of solvent, molar ratio of styrene to H 2O 2, TBA-1* loading on the styrene conversion, styrene oxide yield and selectivity were considered.

Metal states in cobalt- and cobalt–vanadium-modified MCM-41 mesoporous silica catalysts and their activity in selective hydrocarbons oxidation

MCM-41 mesoporous molecular sieves with various V and Co loading were obtained by hydrothermal synthesis. The structural regularity and morphology of the resultant materials were characterized by XRD, TEM, SEM and N 2 adsorption. The information about the nature, co-ordination and location of the metal species were obtained by temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). These methods indicated different localization of the cations in extra-framework positions or in the skeleton of the molecular sieves. In the low loaded cobalt catalysts, Co 2+ in tetrahedral position was observed. The increase in metal content led to the appearance of Co 3+ in Oh symmetry. In both cases, the cobalt ions were placed outside of the silica framework. Vanadium in the bimetallic samples was incorporated inside the framework of the molecular sieves and on the channel walls. V 5+ was in tetrahedral symmetry. Cobalt in the bimetallic samples was presented as Co 2+ in Td symmetry. When Co and V were introduced together in the starting gel, a lower quantity of vanadium was incorporated into the mesoporous sieve. The modified MCM-41 molecular sieves obtained by hydrothermal synthesis were active in selective oxidation of styrene to benzaldehyde and of benzene to phenol.

Epoxidation of styrene over mesoporous Zr–Mn-MCM-41

Epoxidation of styrene with t-butyl hydroperoxide (TBHP) as an oxidizing agent has been conducted under liquid phase reaction conditions over Zr–Mn-MCM-41 with different n Si/( n Zr + n Mn) ratios and Mn-MCM-41(31) catalysts for selective synthesis of styrene oxide. The influences of various reaction parameters such as temperature, time, oxidants, and solvents, styrene to TBHP mmol ratios and acetonitrile (MeCN) to N, N-dimethylformamide (DMF) volume ratios on the conversion of styrene and the selectivity of styrene oxide have also been studied. With the decrease of the n Si/( n Zr + n Mn) ratios of Zr–Mn-MCM-41 catalysts from 327 to 49, the conversion of styrene as well as the yield and selectivity of styrene oxide increase due to the increase of the number of Lewis acid sites on the surface of catalysts. Moreover, the conversion and selectivity in Zr–Mn-MCM-41(49) is higher as compared to that of Mn-MCM-41(31). The Zr–Mn-MCM-41(49) is found to be reusable for the epoxidation of styrene with TBHP for selective synthesis of styrene oxide.

Synthesis of multicarboxylic acid appended imidazolium ionic liquids and their application in palladium-catalyzed selective oxidation of styrene

A series of multicarboxylic acid appended imidazolium ionic liquids (McaILs) with chloride [Cl]– or bromide [Br]– as anions have been synthesized and characterized. Deprotonation of these ionic acids gives the corresponding zwitterions. Re-protonation of the zwitterions with strong Bronsted acids gives a series of new ionic acid-adducts, many of which remained as room-temperature ionic liquids. A new catalytic system, McaIL/PdCl2 for the selective catalytic oxidation of styrene to acetophenone with hydrogen peroxide as an oxidant has been attempted. In the presence of McaILs, it is found that the quantity of palladium chloride PdCl2 used can be greatly reduced while the activity (TOF) and selectivity towards acetophenone are enhanced sharply. It is also shown that the catalytic properties of this system could be finely tuned through the molecular design of the McaILs. The best TOF value obtained so far is 146 h–1 with 100% conversion of styrene at 93% selectivity to acetophenone. In addition, the catalytic activity has been maintained for at least ten catalytic cycles.

Selective oxidation of styrene to acetophenone over supported Au–Pd catalyst with hydrogen peroxide in supercritical carbon dioxide

Selective oxidation of styrene to acetophenone has been investigated for the first time over Pd–Au catalysts with H2O2 in CO2 medium. The influence of the support on the catalytic activity and the product selectivity was investigated, and Al2O3 support showed the best catalytic performance in this system. The presence of CO2 medium could improve the oxidation of styrene to acetophenone and inhibit the formation of by-products. The influence of substituting groups in the aromatic rings of styrene was also discussed.

Preparation of highly ordered Fe-SBA-15 by physical-vapor-infiltration and their application to liquid phase selective oxidation of styrene

A simple physical-vapor-infiltration (PVI) method was applied to prepare highly ordered Fe-containing mesoporous silica SBA-15. The loading amount of Fe in SBA-15 was very high (up to 24 mol%) and can be tuned by using different PVI time. The liquid phase selective oxidation of styrene with H 2O 2 has been used to characterize their catalytic properties, the major product is benzaldehyde and the minor is styrene oxide. Independent of the Fe contents and the heat treatment temperature, the selectivity for benzaldehyde in the reaction at a mild temperature of 50 °C are all above 91%. At elevated temperature of 70 °C, the conversion rate of styrene increases beyond 36% and more significantly the selectivity for benzaldehyde can reach as high as 99%. Comparatively, another two different schemes (simple wet impregnation and incorporation using silane coupling agent) have been also applied to synthesize Fe-containing SBA-15 samples. Under the same condition, the styrene conversion on these two samples are both very low with minor product of phenylacetaldehyde and other styrene oxides.