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

High-electrophilic (SiO)2Nb(OH)(=O) sites confined in silanol defects over Nb-Beta zeolite for efficient cyclic alkene epoxidation reactions

Dealuminated Beta zeolite has a large amount of silanol defects on its interface, which provides an ideal place for embedding metal species and creating metal active sites in a confined microenvironment. The confined metal sites as well as their surroundings are closely related to the reactant activation and transient state achievement. Hence, unraveling the confined metal sites is of great significance for the catalytic reaction process. Herein, niobium species were incorporated into the silanol defects over dealuminated Beta zeolite with a facile dry impregnation method, co-grinding the niobium precursor with dealuminated Beta zeolite support. The successful incorporation of niobium into the silanol defects for 30Nb-Beta zeolite was verified by DRIFT, 1H MAS NMR, UV-Vis and UV-Raman characterizations. XAS characterization and DFT calculations further disclosed that the confined Nb species existed as (SiO)2Nb(OH)(=O), containing two Si-O-Nb bonds, one Nb=O bond as well as one Nb-OH bond. The synthesized 30Nb-Beta zeolite catalyst displayed a superior cyclohexene conversion of 51.1%, cyclohexene oxide selectivity of 83.1% as well as TOF value of 188.2 h-1 ascribed to the inherent electrophilicity of Nb(V) for confined (SiO)2Nb(OH)(=O) species as well as the low oxygen transfer energy barrier for NbV-OOH species. Furthermore, the prepared 30Nb-Beta zeolite can be effectively employed to other cyclic alkene epoxidation reactions.

Kinetic Study of Styrene Oxidation over Titania Catalyst Supported on Sulfonated Fish Bone-derived Carbon

The kinetic evaluation of titania supported sulfonated fish bone-derived carbon (TiO2/SFBC) as a catalyst in styrene oxidation by aqueous hydrogen peroxide was carried out. The catalysts were prepared by carbonation of fishbone powder at varying temperatures 500, 600 and 700 °C, respectively for 2 h, followed by sulfonation with sulfuric acid (1M) for 24 h and impregnated by varied titania concentration 500, 1000 and 1500 µmol. The physical properties of catalysts were characterized using Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX) and the nitrogen adsorption-desorption analysis. The catalytic activity result showed that TiO2/SFBC can be used as a potential catalyst in styrene oxidation. Worth noting that the sulfonation process has not only transformed the TiO2/FBC particulates (without sulfonation) to cuboid-shaped TiO2/SFBC (with sulfonation) but also contributed to the high selectivity of benzaldehyde. On the other hand, carbonization at different temperatures has an indistinct effect on catalytic performance due to their similar surface areas. The styrene conversion rate responded positively with the increasing amount of titania in the functionalized composites. The styrene oxidation by aqueous H2O2 unraveled the first-order reaction with the activation energy of ⁓63.5 kJ. Copyright © 2022 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Dihydroxylation Studies of Isoquinolinones: Synthesis of the EF-Ring of Lysolipin I

Inspired by the potent polycyclic xanthone antibiotic lysolipin I, a general study on asymmetric dihydroxylation reactions of variously substituted isoquinolinones was performed. Different isoquinolinones were efficiently prepared, either by a Pomeranz–Fritsch type condensation or a Curtius rearrangement. Under a broad variety of conventional oxygenation procedures, they proved very unreactive. However, either by suitable substitution of the appending aromatic ring or more forcing conditions a dihydroxylation could finally be performed, which allowed the synthesis of the EF-ring of lysolipin I.

Development of rapid and selective epoxidation of α-pinene using single-step addition of H2O2 in an organic solvent-free process

This study reports substantial improvement in the process for oxidising α-pinene, using environmentally friendly H₂O₂ at high atom economy (∼93%) and selectivity to α-pinene oxide (100%). The epoxidation of α-pinene with H₂O₂ was catalysed by tungsten-based polyoxometalates without any solvent. The variables in the screening parameters were temperatures (30–70 °C), oxidant amount (100–200 mol%), acid concentrations (0.02–0.09 M) and solvent types (i.e., 1,2-dichloroethane, toluene, p-cymene and acetonitrile). Screening the process parameters revealed that almost 100% selective epoxidation of α-pinene to α-pinene oxide was possible with negligible side product formation within a short reaction time (∼20 min), using process conditions of a 50 °C temperature in the absence of solvent and α-pinene/H₂O₂/catalyst molar ratio of 5 : 1 : 0.01. A kinetic investigation showed that the reaction was first-order for α-pinene and catalyst concentration, and a fractional order (∼0.5) for H₂O₂ concentration. The activation energy (E_a) for the epoxidation of α-pinene was ∼35 kJ mol⁻¹. The advantages of the epoxidation reported here are that the reaction could be performed isothermally in an organic solvent-free environment to enhance the reaction rate, achieving nearly 100% selectivity to α-pinene oxide.

Products obtained from the oxidation of α-pinene with hydrogen peroxide (H₂O₂) in the presence of tungsten-based polyoxometalates (α-pinene 1, α-pinene oxide 2, pinanediol 3, campholenic aldehyde 4, sobrerol 5, verbenol 6 and verbenone 7).

Enhanced activity and water tolerance promoted by Ce on MnO/ZSM-5 for ozone decomposition

Catalytic decomposition is a promising way to eliminate ozone using manganese oxides. However, water-induced deactivation of the catalysts remains a challenge for further application. In this work, a series of Ce-promoted MnO supported on ZSM-5 (Mn-xCe/ZSM-5) were developed for ozone decomposition, which exhibited superior catalytic performance. The catalysts were characterized by multiple techniques. It is indicated that MnO was highly dispersed on ZSM-5 (Mn/ZSM-5), accounting for the high performance of ozone decomposition. Addition of Ce in Mn/ZSM-5 formed abundant redox pairs that promoted electron transfer, and thus exhibited superior ozone decomposition activity. Mn-3Ce/ZSM-5 with medium Ce loading showed the maximum activity by exposing the most active sites. Furthermore, Mn-3Ce/ZSM-5 was highly water-resistant in comparison with Mn/ZSM-5 by modulating the surface acidic property to be beneficial for the water desorption. This work provides an efficient and facile way to fabricate Ce-promoted Mn with low valence for effective and stable decomposition of ozone at room temperature.

Vanadyl β-tetrabromoporphyrin: synthesis, crystal structure and its use as an efficient and selective catalyst for olefin epoxidation in aqueous medium

We hereby report the synthesis, characterization and catalytic applications in the epoxidation of alkenes by a vanadyl porphyrin having bulky bromo substituents at the β-positions viz. vanandyltetrabromotetraphenylporphyrin (1). The synthesized porphyrin was characterized by various spectroscopic techniques like UV-visible, FT-IR, EPR, MALDI-TOF mass spectrometry and single crystal X-ray analysis. Porphyrin 1 has a nonplanar structure as indicated by its X-ray structure, DFT and electrochemical studies. 1 was analyzed for its catalytic application in the epoxidation of various alkenes. The catalytic reactions were carried out in CH₃CN/H₂O mixture in 3 : 1 (v/v) ratio. 1 displayed good efficiency in terms of mild reaction conditions, lower reaction temperature and minimal catalyst amount consumption. 1 exhibited excellent selectivity, high conversion efficiency and huge TOF (7600–9800 h⁻¹) in a significantly low reaction time of 0.5 h. Catalyst 1 was regenerated at the end of various catalytic cycles making it reusable and industrially important.

We have synthesized β-tetrabromo-meso-tetraphenylporphyrinatooxidovanadium(iv) (VOTPPBr₄) which possesses high thermal stability and nonplanar macrocyclic core. Further, it was utilized for selective epoxidation of olefins in good yields with very high TOF numbers.

High pH promoting the synthesis of V-Silicalite-1 with high vanadium content in the framework and its catalytic performance in selective oxidation of styrene

V-Silicalite-1 with a high vanadium content in the framework was synthesized. OH⁻ ions effectively promoted the entry of vanadium atoms into the framework. The V-Silicalite-1 exhibited good catalytic performance.

Influence of the nature and environment of manganese in Mn-BEA zeolites on NO conversion in selective catalytic reduction with ammonia

Manganese-containing BEA zeolites, Mn_xSiBEA (x = 1-4 wt%) and Mn_(I.E.)AlBEA, were prepared by a two-step post-synthesis method and a conventional wet ion-exchange, respectively, and applied as catalysts in the selective catalytic reduction of NO with ammonia (NH₃-SCR). The physicochemical analysis of zeolite properties by high-energy-resolution fluorescence-detected XANES (HERFD-XANES) and X-ray emission spectroscopy (XES) uncovered that the coordination, geometry and oxidation state of Mn species are strongly related to the preparation method. Additionally, the study of catalyst acidity by FTIR spectroscopy with CO and pyridine probe molecules provided important insight into the number and type of acidic centres present on the catalyst surface. The catalytic results revealed that NO conversion depended on the state and content of Mn. The zeolites obtained by the two-step post-synthesis method and with a low Mn content were very active in the medium temperature range (NO conversion ∼100%) with simultaneous high selectivity to N₂ due to the presence of isolated, framework Mn(iii) and Mn(ii) species. The N₂O formation was especially high in the case of catalysts containing extra-framework polynuclear Mn species and negligible in the case of Mn_(I.E.)AlBEA containing predominantly isolated, extra-framework Mn(ii) species.

Incorporation of Mn into the vacant T-atom sites of a BEA zeolite as isolated, mononuclear Mn: FTIR, XPS, EPR and DR UV-Vis studies

A MnSiBEA zeolite has been prepared via a two-step postsynthesis procedure which consisted, in the first step, of the treatment of a tetraethylammonium BEA zeolite with nitric acid for the formation of vacant T-atom sites and then, in the second step, of the incorporation of Mn ions into the framework, resulting in a SiBEA zeolite, through their reaction with the silanol group of the vacant T-atom sites. The incorporation of Mn ions into the framework of the SiBEA zeolite has been evidenced using XRD. The formation of isolated mononuclear Mn(ii) and Mn(iii) in a MnSiBEA zeolite has been shown using FTIR, diffuse reflectance UV-Vis, EPR and XPS. The acidic properties of the mononuclear manganese species have been investigated via FTIR spectroscopy using pyridine as the probe molecule. The changes in the oxidation state of the Mn species under various treatments have been proven using EPR.

Partial-Redox-Promoted Mn Cycling of Mn(II)-Doped Heterogeneous Catalyst for Efficient H2O2-Mediated Oxidation

The development of a heterogeneous catalyst with high catalytic activity and durability for H₂O₂-mediated oxidation is one of the most important industrial and environmental issues. In this study, a Mn(II)-doped TiO₂ heterogeneous catalyst was developed for H₂O₂-mediated oxidation. The TiO₂ substrate-dependent partial-redox behavior of Mn was identified on the basis of our density functional theory simulations. This unique redox cycle was induced by a moderate electron transfer from Ti to Mn, which compensated for the electron loss of Mn and finally resulted in a high-efficiency cycling of Mn between its oxidized and reduced forms. In light of the theoretical results, a Mn(II)-doped TiO₂ composite with well-defined morphology and large surface area (153.3 m² g^-1) was elaborately fabricated through incorporating Mn(II) ions into a TiO₂ nanoflower, and further tested as the catalyst for oxidative degradation of organic pollutants in the presence of H₂O₂. Benefiting from the remarkable textural features and excellent Mn cycling property, this composite exhibited superior catalytic performance for organic pollutant degradation. Moreover, it could retain 98.40% of its initial activity even in the fifth cycle. Our study provides an effective strategy for designing heterogeneous catalytic systems for H₂O₂-mediated oxidations.

Titania-Loaded Coal Char as Catalyst in Oxidation of Styrene with Aqueous Hydrogen Peroxide

Titania-loaded coal char catalyst was successfully prepared. The preparation steps involved pyrolysis of low rank coal at different temperatures and durations, sulfonation, impregnation of titanium(IV) isopropoxide, and then heating at 110 °C. It is found that the coal chars’ surfaces were rough after sulfonation and impregnation, while large pore volume, high surface area and carbon composition were observed at low pyrolysis temperature for short duration. These properties contributed to high selectivity towards benzaldehyde (> 90 %) at 600 °C (0.5–2 h)) in styrene oxidation using aqueous hydrogen peroxide as the oxidant.

ZSM-5 functionalized in situ with manganese ions for the catalytic oxidation of cyclohexane

We report the preparation of transition metal-containing ZSM-5 catalysts, which were active and selective for cyclohexane oxidation.

Manganese(iii)salophen supported on a silica containing triazine dendrimer: an efficient catalyst for epoxidation of alkenes with sodium periodate

Mn(iii) salophen supported on a nanosilica triazine dendrimer was synthesized and used for epoxidation of alkenes with sodium periodate.

Alkaline niobates ANbO3 (A = Li, Na, K) as heterogeneous catalysts for dipropyl sulfide oxidation

Alkaline ANbO₃ (A = Li, Na, K) niobates with perovskite type structure were prepared by sol gel method, extensively characterized and evaluated as heterogeneous catalysts for selective oxidation of dipropyl sulfide to its corresponding sulfoxide.

An efficient epoxidation of terminal aliphatic alkenes over heterogeneous catalysts: when solvent matters

With a peculiar combination of catalyst/oxidant/solvent, it is possible to obtain good yields and excellent selectivities in the epoxidation of 1-octene.

Efficient synthesis of p-chlorobenzaldehyde through liquid-phase oxidation of p-chlorotoluene using manganese-containing ZSM-5 as catalyst

Efficient synthesis of p-chlorobenzaldehyde by liquid-phase oxidation of p-chlorotoluene with molecular oxygen was achieved over Mn–ZSM-5 (Si/Mn = 48, Mn 1.7 wt%).

Metal ion-exchanged zeolites as highly active solid acid catalysts for the green synthesis of glycerol carbonate from glycerol

The application of metal ion-exchanged zeolites as highly efficient catalysts for the synthesis of glycerol carbonate from glycerol carbonylation is reported.

Preparation of SnO2/graphene nanocomposite and its application to the catalytic epoxidation of alkenes with H2O2

The SnO₂/graphene nanocomposites have been achieved via hydrothermal method and used as an efficient catalyst for the epoxidation of alkenes with H₂O₂ in nitrile based systems for the first time.

Metal ion-exchanged zeolites as solid acid catalysts for the green synthesis of nopol from Prins reaction

The application of metal ion-exchanged zeolites as highly active and selective catalysts for the synthesis of nopol from the Prins reaction of β-pinene is reported.

Magnetic Nanoparticles Supported Binuclear Manganese(II) Complex via Covalent Interaction: A Highly Efficient and Reusable Catalyst for the Epoxidation of Cyclohexene

In the present work, the highly efficient epoxidation of cyclohexene catalyzed by Fe3O4@SiO2/([Mn2L(HL)(H2O)4], is reported. First, the Fe3O4@SiO2 nanoparticles were modified with (3-chloropropyl)-trimethoxysilane (CPTMS) group and then [Mn2(HL)2(H2O)4] was attached to the support via covalent linkages. The prepared catalyst was characterized by spectroscopic studies and chemical analyses. This catalytic system serves as catalyst for the oxidation of cyclohexene to cyclohexene epoxide and 2-cyclohexene-1-ol using H2O2 as an oxidant. Thus, this catalytic system shows high activity and selectivity toward cyclohexene epoxide. Also activity of the immobilized catalyst remains nearly unchanged after five cycles, that it is truly heterogeneous.