Liquid-phase Epoxidation Of Alkenes Research Articles

Enhanced catalytic oxidation performance of K+-modified Ti-MWW through selective breaking of interfacial hydrogen-bonding interactions of H2O2

Cationic modification was applied to Ti-MWW zeolite via the treatment of potassium chloride (KCl). Compared to the original Ti-MWW zeolite, the K-modified Ti-MWW sample (Ti-MWW-K) exhibited much improved catalytic activity, selectivity and stability in the liquid-phase epoxidation of alkenes. Our investigation shows that the K+ modification has negligible effect on the physicochemical properties, the state of the Ti active sites and the Lewis acidic strength of the Ti-MWW catalyst. Our result has further indicated that breaking of the hydrogen-bonding interactions between the Oβ atom of H2O2 (Hα-Oα-Oβ-Hend) and the H atom of the silanols adjacent to the Ti-OH (SiOH(HOTi)) in the Ti-MWW-K zeolite promotes the activation of H2O2, which is responsible for its superior catalytic oxidation activity. This finding helps shed light on utilizing the hydrogen-bonding interactions based on the titanosilicates/H2O2 system to achieve the excellent catalytic oxidation performance.

Easily recoverable micron-sized silica-walled TS-1 colloidosomes: Preparation and application as liquid-phase alkene epoxidation catalysts

Ultrafine hierarchical TS-1 zeolite (<300nm) generally expresses eminent catalytic activity for liquid-phase alkene epoxidation, but encounters serious separation difficulties. Micron-sized silica-walled TS-1 colloidosomes, which were synthesized via an interfacial sol-gel method, can effectively resolve fine TS-1 zeolite separation problems. The interfacial sol-gel process involves construction of a stable W/O Pickering emulsion stabilized by fine TS-1 particles and alkali-catalyzed hydrolysis of silica precursor methyl-trimethoxysilane at the oil-water interface. The successful preparation of TS-1 colloidosome was verified by Scanning electron microscopy (SEM) and Energy dispersive X-ray spectroscopy (EDS). The prepared TS-1 colloidosome dimension is tailorable according to water-to-oil volume ratio (Rw/o) and ratio of TS-1 wt to oil volume (Rs/o). On the same time, X-ray diffraction patterns and UV–vis spectra disclosed that the interfacial sol-gel process had no effect on the MFI structure of hierarchical TS-1 particles. The catalytic results showed that the prepared TS-1 colloidosome was a very active and stable catalyst for liquid-phase alkene epoxidation reactions.

Mesoporous molecular sieves containing niobium(V) as catalysts for the epoxidation of fatty acid methyl esters and rapeseed oil

Niobium-containing mesoporous silica (Nb–SiO2) catalysts, which showed previously promising performances in the liquid-phase epoxidation of alkenes, were here applied to the epoxidation of unsaturated fatty acid methyl esters (FAMEs), selectively hydrogenated FAMEs and rapeseed oil triglyceride with aqueous hydrogen peroxide. Niobium-silica solids were prepared via grafting of niobocene dichloride onto the surface of different porous silica-based supports (non-ordered SiO2, ordered mesoporous MCM-41 and SBA-15 molecular sieves) via a dry impregnation procedure. Promising performance with very good selectivity towards desired monoepoxides were obtained, in particular over a Nb-grafted silica catalyst prepared from a commercial non-ordered silica support.

Mass Transfer Effect on the Oxidation of Alkenes and Phenol with Hydrogen Peroxide Using TS-1 Titanosilicate as a Catalyst

Liquid-phase epoxidation of alkenes and hydroxylation of phenol were carried out using TS-1 titanosilicate as a catalyst with the particle sizes ranging from 0.15 up to 25 µm. Experimental reaction rates as measured on the smallest catalyst particles were found to be free of mass transfer influence. This makes it possible to describe quantitatively the internal diffusion effects for large-size grains, so as to evaluate the values of reagent diffusion coefficients within the catalyst pores.

Nanocluster polyoxomolybdate supported on natural zeolite: a green and recyclable catalyst for epoxidation of alkenes

A heterogeneous catalyst for epoxidation of alkenes has been synthesized by introducing polyoxomolybdate into a natural zeolite as a solid and green support. The prepared catalyst was characterized by FT-IR, inductively coupled plasma optical emission spectrometry (ICP-OES), powder X-ray diffraction (XRD), N2 absorption–desorption, field emission scanning electron micrograph (FE-SEM) and transmission electron microscopy (TEM). The catalytic investigations disclosed that nanocluster polyoxomolybdate supported on the surface is an active and recyclable catalyst in liquid phase alkene epoxidation in dichloroethane at 80 °C.

Synthesis of two titanosilicates with distinct interlayer connections from similar gels.

Ti-SSZ-70 and Ti-ECNU-6, with identical intralayer structures but distinct interlayer connections, were prepared from similar synthetic gels free of alkali metal ions and boric acid. Ti-SSZ-70, composed of vertically misaligned MWW layers, was transferred to Ti-ECNU-6, structurally analogous to the Ti-MWW zeolite with a well-aligned layer stacking, upon the addition of an appropriate amount of hexamethyleneimine to the gel. These two titanosilicate catalysts exhibited outstanding catalytic activities in the liquid-phase alkene epoxidation.

First stable nitrate-encapsulated sandwich type polyoxometalate: Synthesis, structural characterization, and catalytic performance

A stable sandwich type Keggin polyoxometalate, Na4K5[K3Cu3(NO3)(A-α-PW9O34)2], has been synthesized and crystallized by a simple reaction method. Elemental analysis, FTIR, UV–vis, X-ray single crystal, thermal gravimetry, and cyclic voltammetry were used for the characterization of synthesized POM. The TBA salt of [K3Cu3(PW9O34)2]9− revealed high catalytic activity and 74–99% selectivity in the liquid phase epoxidation of alkenes with aqueous H2O2. The X-ray structure of this complex reveals that three Cu(II) ions are sandwiched between two A-α-PW9O34 moieties and that a nitrate monoanion is encapsulated in the same plane as the three Cu(II) atoms. The nitrate is coplanar with the three copper atoms, which are each in a distorted square-pyramidal environment. After recrystallization, the NO3− group in the central belt didn't exit, in which this phenomenon is attributed to the type of counterion in the complex (as a result of mixing Na+ and K+ as counterions). This compound showed excellent stability in different pH and also didn't dissociate with hydrogen peroxide.

Selective epoxidation of alkenes with hydrogen peroxide over efficient and recyclable manganese oxides

Abstract A series of manganese oxides (MnO, Mn3O4, Mn2O3 and MnO2) were prepared and firstly applied as heterogeneous catalysts for the liquid phase epoxidation of alkenes with 30% H2O2 in bicarbonate solution. Under our experimental conditions, MnO exhibited superior activity for the conversion of styrene to achieve ca. 100% with 92.4% selectivity of epoxide, compared to the other three manganese oxides as well as other metal oxides. Furthermore, recycling studies showed the good recyclability of MnO as a heterogeneous catalyst, which did not lose the catalytic activity after four reuses appreciably.

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.

Liquid-phase Epoxidation of Alkenes Using Molecular Oxygen Catalyzed by Vanadium Cation-exchanged Montmorillonite

Abstract Vanadium cation-exchanged montmorillonite can efficiently catalyze the selective epoxidation of various alkenes and the oxygenation of adamantane using molecular oxygen as a sole oxidant.

Controlled detitanation of ETS-10 materials through the post-synthetic treatment and their applications to the liquid-phase epoxidation of alkenes

Treatments of ETS-10 titanosilicates with HCl, NH 4Cl or citric acid led to the change in the coordination environment of Ti. These treatments also led to the partial extraction of Ti from the framework of ETS-10. The local structural changes brought about the formation of the active sites for the epoxidation of cyclohexene with H 2O 2. The highest epoxidation activity and efficiency of H 2O 2 as an oxidant were achieved when the original [Na, K]-type ETS-10 was treated with 3.7 mol dm −3 NH 4Cl solution followed by the calcination at 723 K.

Solid-Phase Immobilization of a New Epoxidation Catalyst.

The heterogenization of a titanium(IV) silsesquioxane complex in an MCM-41 molecular sieve, by tailoring the polarity of MCM-41, results in self-assembled materials (see the space-filling model on the right) that are active, truly heterogeneous, and recyclable catalysts for liquid-phase alkene epoxidation.

Probing active sites in solid catalysts for the liquid-phase epoxidation of alkenes

Using X-ray absorption fine structure measurements with a synchrotron source, the local environment of the titanium-centred active site of a siliceous mesoporous catalyst for the epoxidation of cyclohexane by H2O2 has been determined prior to the onset and during the course of catalysis.

Vanadium site in VAPO-5: Characterization and catalytic properties in liquid-phase alkene epoxidation and benzylic oxidation

Solid state NMR ( 51V, 27Al, 31P) and ESR were used to characterize the vanadium site in VAPO-5, as obtained by a fluoride-assisted synthesis. It was found that the main species at low vanadium content is a monomeric vanadyl unit in square pyramidal or distorted octahedral coordination, both in oxidation state (IV) for the as-synthesized material and in oxidation state (V) for the calcined material. Chemical compositions of the samples and site geometries strongly suggest a phosphate environment, and vanadyl ions are thought to occupy aluminium sites. At higher vanadium contents (1.3% V/(V+Al+P) atomic ratio) tetrahedral vanadium (V) is also formed upon calcination. At 3.0% V/(V+Al+P), the material is not entirely stable towards calcination. The vanadium species readily interacts with water, tert-butanol and tert-butyl hydroperoxide (TBHP). VAPO-5 was found to be an active and very selective catalyst for the epoxidation of allylic alcohols with TBHP. It also catalyses the epoxidation of simple alkenes and the side chain oxygenation of aromatics using the same oxidant. The epoxidation reactions involve a heterolytic oxygen transfer from what is probably a vanadium alkylperoxo surface complex.