Epoxidation Reaction Research Articles

Facet and dual vacancy engineering-boosting BiOBr for enhanced CO2 and epoxide cycloaddition reaction under mild and cocatalyst-free conditions: Double substrate active sites and activated surface bromine ions synergy

Among the many strategies for CO2 resource utilization, the synthetic technology of cyclic carbonates with 100 % atom economy through CO2and epoxide is one of the most industrially viable routes, but its efficiency has been severely hampered by the lack of highly active catalytic sites. Moreover, due to the intrinsic thermodynamic stability and kinetic inertia of CO2 and the higher energy barrier of the ring-opening reaction of epoxides, the heterogeneous catalytic conversion of CO2 highly depends on harsh operating conditions, high temperatures and pressures, and the incorporation of cocatalysts. The development of efficient heterogeneous catalysts for CO2 conversion under cocatalyst-free and mild conditions has always been a challenge. Herein, we have proposed a synergetic strategy of facet and vacancy engineering for the construction of highly efficient heterogeneous catalyst BiO1-xBr1-y-(010) for CO2 cycloaddition, where introducing the OVs-BrVs pairs into typical (010) facets BiOBr with simultaneous surface Lewis acid sites Bi3+ and nucleophilic sites Br−. By combining theoretical calculations and a series of systematic experiments, such as CO2 temperature-programmed desorption, electron paramagnetic resonance and fluorescence probe analysis experiments, the introduced OVs-BrVs pair can not only form Bi3+-Bi(3-x)+ dual active sites on the surface, which activate PO and CO2 respectively to reduce the energy barrier of CO2 insertion, but also activate Br− near BrVs to enhance their nucleophilic attacking ability and reduce the energy barrier of epoxides ring-opening. As a result, the BiO1-xBr1-y-(010) with abundant surface OVs-BrVs pairs showed a high cyclic carbonates conversion of 99 % with 100 % selectivity under cocatalyst-free and mild conditions, far surpassing most heterogeneous catalytic systems. This work provides a completely new strategy to construct high-performance heterogeneous CO2 cycloaddition catalysts through a simple facet and vacancy engineering strategy to overcome the harsh operating conditions limitation and the use of cocatalysts.

Synthesis of bio‐based plasticizer from custard apple seed oil for PVC application

AbstractIn the research, a bio‐based through epoxidizing, plasticizer was created non‐toxic custard apple seed oil (CASO) using peroxy acid generated in situ and investigates the application of a bio‐based plasticizer in the compounding of polyvinyl chloride as epoxidized custard apple seed oil (ECASO) (PVC). The ECASO was synthesized through an epoxidation reaction and characterized using Fourier‐transform infrared spectroscopy and analytical parameters such as epoxy value, and oxirane conversion. To create plasticized PVC, the PVC was mixed with different ratios of ECASO and dioctyl phthalate (DOP) using a two‐roll mill and prepared PVC sheet by compression molding. The ECASO plasticizer completely fuses with PVC and plasticized PVC sheets are made. Glass transition temperature, tensile strength, percent elongation, solvent resistance, differential scanning calorimetry (DSC), and thermal gravimetric analysis were among the mechanical and thermal characteristics of PVC sheets that were assessed. This result shows the plasticization efficiency of ECASO and DOP combined was similar to that of DOP alone, even with the same plasticizer loading. Moreover, when used in combination with DOP, ECASO was found to be a more efficient plasticizer. As a result, ECASO can be used as a biobased substitute for DOP, replacing up to 60% of the ECASO plasticizer loading.

Synthesis and properties of bio‐based environmental plasticizer derived from oleic acid for poly (vinyl chloride)

AbstractUsing the abundant and cost‐effective oleic acid and isosorbide with excellent properties as raw materials, the plasticizers of isosorbide di‐oleate (IDO) and isosorbide di‐epoxidized oleate (IDEO) with good plasticizing effect, low cost and green safety were synthesized by esterification and epoxidation reaction. The molecular structure of the synthesized plasticizers was characterized by FT‐IR and 1H NMR. The PVC shows better flexibility when IDEO or IDO plasticizer is used than commercial DOP. In particular, IDEO‐40 has 34% higher tensile strength and 17% higher elongation at break than DOP‐40. The introduction of epoxy groups on the carbon–carbon double bond of fatty acids meets the high thermal stability of plasticized film. The residual amount of IDEO‐40 is 7.01%, and at a high temperature of 180 °C, it can maintain high heat resistance for more than 220 min and transmittance of over 86%. Moreover, IDEO demonstrates excellent resistance to migration and volatilization. However, PVC films plasticized with IDO display reduced mechanical properties, cold resistance, and resistance to volatilization and migration due to the presence of non‐rotating carbon–carbon double bonds. The results indicate that these bio‐based plasticizers hold promise for practical applications in PVC products, offering improved environmental sustainability and performance characteristics.

The self-assembly of tetranuclear [Gd4] cluster: Magnetic refrigeration and efficient CO2 chemical fixation

In this paper, the self-assembly of Gd3+ ions and ligand 5-chlorine-8-hydroxylquinoline (HL) successfully generated one tetranuclear lanthanide compound [Gd4(µ3-OH)2(L)6(acac)4] (1) (L = 5-chlorine-8-hydroxylquinoline; Hacac = acetylacetone), in which four Gd3+ ions are connected into a [Gd4O2] cluster. Magnetic studies revealed that anti-ferromagnetic interactions between neighbouring Gd3+ ions were observed in 1. In addition, 1 also shows magnetocaloric effect and the −ΔSm value reaches 28.05 J kg−1 K−1 at T = 2.0 K and ΔH = 7 T. Catalytic experiments indicated that 1 and tetra-n-butylammonium bromide (TBAB) could synergistically catalyze the cycloaddition reaction of CO2 and epoxides at relatively mild condition.

Porous Coordination Polymer MOF-808 as an Effective Catalyst to Enhance Sustainable Chemical Processes.

The improvement of sustainable chemical processes plays a pivotal role in safe environmental and societal development, for example, by reducing the use of hazardous substances, preventing chemical waste, and improving the efficiency of chemical reactions to obtain added-value compounds. In this context, the porous coordination polymer MOF-808 (MOF, metal-organic framework) was prepared by a straightforward method in water, at room temperature, and was unequivocally characterized by powder X-ray diffraction, vibrational spectroscopy, thermogravimetric analysis, and scanning electron microscopy. MOF-808 material was applied for the first time as catalysts in ring-opening aminolysis reactions of epoxides. It demonstrated high activity and selectivity for reactions of styrene oxide and cyclohexene oxide with aniline, using a very low amount of an eco-sustainable solvent (0.5 mL of EtOH), at 70 °C. Moreover, MOF-808 demonstrated high stability in the catalytic reaction conditions applied, and a notable reuse capacity of up to 20 consecutive reaction cycles, without significant variation in its catalytic performance. In fact, this Zr-based porous coordination polymer prepared by environment-friendly conditions proved to be a novel efficient heterogeneous catalyst, promoting the ring-opening reaction of epoxides under more sustainable conditions, and using a very low amount of catalyst.

Classical curing of epoxy modified lignin with polyamine for new Epoxy-Polyimine composite

Lignin, which is the most abundant aromatic polymer in nature was used as a green substitute for the toxic bisphenol A. Here we synthesized the epoxy agent from lignin by reacting lignin with epichlorohydrin. Further this product was reacted with the lignin-amine to give the new epoxy-polyimine composites. This study evaluated the curing of bio-based epoxy resins derived from lignin with aromatic and an aliphatic amine. The thermal stability of the cured lignin-based epoxy samples was evaluated. Epoxidation is an interesting way to develop new uses and applications of lignin. Lignin-based epoxy resins were obtained by the epoxidation reaction using the lignin recovered directly from pulping liquor. For the epoxidation reaction it was optimized the influence of the lignin:NaOH (w/w) ratio, temperature and time of the reaction on the properties of the prepared epoxidized lignin. The structures of lignin-based epoxy resins were evaluated by epoxy index test and FTIR spectroscopy. Optimal conditions were obtained for lignin-based epoxy resin produced at lignin/NaOH = 1/3 at 80 °C for 3 h. Thermogravimetry analysis (TGA) revealed that epoxidation enhances the thermal stability of lignin and may allow a wider temperature range for various applications.

Research on the production technology of rubber epoxy from concentrated natural rubber latex

The results of research on epoxidation technology from concentrated natural rubber latex (CNRL) and in-situ peroxyformic acid, which is synthesised from formic acid (FA) and hydrogen peroxide (HP), are presented in the article. The study investigated the influence of technological parameters of the epoxidation process, such as stabiliser content (nonylphenol ethoxylate, NP9), dry rubber content (DRC), isoprene, stirring speed, reaction time, reaction temperature, and molar ratios of hydrogen peroxide and isoprene (IP), on the epoxy resin content of the product. Research results have shown that the epoxidation reaction with NP9 at 10% takes from 2.5 to 20 hours under the following conditions: latex composition contains from 16 to 24% DRC, stirring speed 100 rpm, reaction temperature response 30 to 70 °C, HP/IP molar ratio changes from 0.7 to 1.3, FA/IP ratio is 0.2, the product was stable and without coagulation. The product was obtained with an epoxy content of 23.4 to 43.6%. This is the basis for building an epoxidized natural rubber (ENR) production process to create a series of natural rubber products that are renewable, environmentally friendly, low-cost, and have many industrial applications.

Short Term Silver Electrode Microstructure Changes Under Epoxidation Conditions for Solid Oxide Electrolysis Cells

Ethylene epoxidation is an important reaction forming ethylene oxide (EO), which is a precursor to many other critical chemicals. This study links short-term EO production to the effects on the microstructure of Ag/yttria-stabilized zirconia cells with and without electrochemical promotion of catalysis (EPOC). Nano-scale features, called striations, were observed on the silver under all epoxidation reaction conditions tested, using a scanning electron microscope. While appearing in both cases, the striations for the EPOC case are finer in size (∼150 to 250 nm) compared to the no current case (∼400 to 500 nm). These features did not appear when epoxidation conditions were not present. Striation formation was further linked to the epoxidation reaction through electrochemical impedance spectroscopy and gas chromatography. Ethylene conversion to EO declines over the course of hours as striations form, indicating that striations have a negative influence on the reaction. Distribution of relaxation times was performed to determine the effect striation formation has on the electrochemical performance of the cells. It was observed that the low-frequency peaks in the DRT analysis significantly decrease as striations formed over the course of 10 h.

One-step synthesis of hydroxyl-functionalized ionic hyper-cross-linked polymers with high surface areas for efficient CO2 capture and fixation

Ionic liquid-based functional materials have attracted significant attention for their distinctive structure in the field of CO2 capture and conversion. In this work, a series of hydroxyl-functionalized ionic hyper-cross-linked polymers are prepared through a one-step Friedel-Crafts reaction involving hypoxanthine (HX) and benzimidazole (BI) as the monomers, along with various halohydrocarbon crosslinking agents. These polymers demonstrate a high specific surface area (558–1480 m2·g−1), well-developed microporous structure, and unique ion sites, enabling them to exhibit remarkable and reversible CO2 adsorption properties. Particularly noteworthy is their CO2 adsorption capacity, which surpasses that of similar ionic polymers documented in the literature, reaching 157.5 mg·g−1 at 273 K and 1 bar. Additionally, these polymers function as recyclable catalysts in the cycloaddition reaction of CO2 and epoxides, enabling the conversion of CO2 into cyclic carbonates with yields of up to 99 % even without a co-catalyst. Mechanism investigation reveals that the introduction of hydroxyl groups in the polymer is the key to improving catalytic activity through a synergistic catalytic effect. This research provides a novel concept for designing ionic functional materials with capabilities in both CO2 adsorption and catalytic activity.

Polymer Mechanochemistry on Reactive Species Generated from Mechanochemical Reactions†

Comprehensive SummaryPolymer mechanochemistry on reactive species has attracted more and more attentions over the past 20 years, as the mechanochemical generation of reactive species has a great potential in developing different polymeric materials for various purposes, such as stress detection, self‐healing, self‐strengthening, controllable degradation and release of small molecules. In this review, we first discuss the recent progress on polymer mechanochemistry of the reactive species that are generated from the mechanochemical reactions of mechanophores. Five types of reactive species, including radical, zwitterion, ionic, carbene and neutral intermediates, and their applications were reviewed in detail. Since mechanochemical reactions are sensitive to the mechanophore structure and polymer framework, we then discuss how mechanophore isomerism, polymer structure, polymer attachment point, and polymer architecture influence the mechanophore activation. At last, we provide our perspectives on the polymer mechanochemistry of reactive species. Key ScientistsIn the 1930s, a seminal work by Staudinger showed that the molecular weight of poly(styrene) reduced after mastication. However, polymer mechanochemistry mainly focused on the destructive effects of mechanical force, until Moore reported that the azo‐mechanophore was cleaved selectively upon sonication in 2005. Afterwards, his group also found that mechanical force changed the reaction pathway of benzocyclobutene and made spiropyran display purple color under stress. In 2009, Sijbesma revealed that metal–NHC could be used as a latent catalyst to catalyze transesterification and polymerization. Subsequently, the Craig group disclosed the special mechanical reactivity of perfluorocyclobutane in 2011 and examined the influence of polymer backbone on the reactivity of epoxides in 2012. Later, they also reported that the lever‐arm effect enhanced gDBC or gDCC mechanochemistry. Since 2015, Otsuka's group has developed a series of mechanophores that generated various carbon radicals and showed different colors under mechanical force. De Bo subsequently investigated the effect of regio‐ and stereochemistry on the reactivity of furan–maleimide adduct in 2017, and he examined the different mechanisms of the mechanical activation of tetrafluorobenzene–NHC (N‐heterocyclic carbene) adduct in 2020. During that time, the Choi group explored the influence of polymer architecture on the mechanophore activation, and Robb's group utilized a furan‐maleimide adduct to achieve the release of different small molecules. In 2020, Göstl and Herrmann employed the scission of the disulfide within polymers to release drugs and reporting molecules by ultrasound, and the Chen group also investigated the mechanochemistry of diselenides which afforded selenium radicals. In 2021, Boydston's group realized the “flex‐activation” of NHC‐carbodiimide to release NHC small molecules. Recently, the Chen group achieved multistate mechanochromism by combining two Rh structures together through a conjugated connector. In addition, Robb designed a furan‐maleimide adduct to mechanically give a donor–acceptor Stenhouse adduct that reacted with different amines to display various colors. This review has focused on the chemistry of reactive species that are generated from mechanochemical reactions.

What leads to direct epoxidation? An exhaustive DFT investigation of electrophilic oxygen mediated epoxidation of ethylene on Ag(100)

Extensive research has contributed to a better understanding of the commercially important epoxidation reaction. Selectivity, a crucial aspect of this reaction, has received significant attention in both experimental and theoretical investigations. However, a consensus regarding the role of electrophilic oxygen in epoxidation is yet to be reached. The present study is a theoretical examination of the prerequisites necessary for direct epoxidation to occur on the Ag(100) surface, at varied monolayer concentrations. Additionally, the study investigates the characteristics of various oxygen species interacting with ethylene to promote the direct epoxidation pathway. Based on the effective charges and projected density of states (pDOS) analysis, three oxygen variants were identified on the Ag(100) surface: atomic oxygen, dissociatively adsorbed molecular oxygen, and O3. The investigation reveals that all oxygen species, despite their physical and electronic differences, are electrophilic and undergo direct epoxidation. This work provides insights into the complex nature of epoxidation reaction and discusses electronic factors influencing the selective oxidation route on different AgO complexes.

Fast and sustainable CO2 conversion to propylene carbonate using fluoroalcohol-based bifunctional ionic liquids: Insights from experiments and theoretical simulations

We report on the metal-free and rapid catalytic conversion of carbon dioxide into cyclic carbonates under solventless conditions utilizing novel bifunctional fluoroalcohol-based ionic liquids (FBILs) as catalsyts. In the presence of 2.5 mol% 4-(1,1,1,3,3,3-hexafluoro-2-hydroxyisopropyl) phenyl trimethylammonium iodide (FBIL-1), under 0.1 MPa and 90 °C, excellent yield of propylene carbonate(>95%) was achieved in 1 h, which significantly shortens the reaction time, compared with the conventional catalysts. DFT calculations reveal that FBILs with fluorine-substituted hydroxyl groups exhibit stronger hydrogen bonding with epoxides compared to ILs lacking fluorine substitutions. The hydrogen bond length for ILF/PO is 1.658 Å, shorter than that for IL/PO (1.813 Å). This characteristic contributes to reducing the activation energy for the ring-opening reaction of epoxides. In the ILF/PO system, the reaction barrier is 88.72 kJ·mol−1, lower than the 101.46 kJ·mol−1 barrier for IL/PO, allowing the former to more rapidly facilitate the fixation of carbon dioxide into cyclic carbonates. Besides high catalytic efficiency, these FBILs have the characteristics of a facile synthesis route and easy post-reaction recovery.

Dual hydrogen bond donor functionalized hierarchical porous poly(ionic liquid)s for efficient CO2 fixation into cyclic carbonates

CO2 capture and conversion to high-value-added products is critical for the purposes of environmental preservation and carbon resource utilization. In this study, a novel class of porous poly(ionic liquid)s has been synthesized, incorporating dual hydrogen bond donors (amide and hydroxyl groups) and nucleophiles (Br-) as multiple effective active sites for the cycloaddition reaction between CO2 and epoxides. The presence of dual hydrogen bond donors not only provides two active sites for synergistic catalysis with epoxides but also enhances the capacity for CO2 adsorption. Comprehensive characterization has been conducted to elucidate the structural features and properties of these innovative materials. By regulating the ratio between ionic liquid monomer and divinylbenzene, a hierarchical porous structure favorable for the reaction was constructed, resulting in optimized catalytic activity comparable to that of bulk ionic liquid monomers. Furthermore, this catalyst exhibits remarkable structural stability with minimal activity loss even after five consecutive use cycles. Combining density functional theory calculations with in-situ Fourier transform infrared spectroscopy analysis, the catalytic mechanism was proposed that the dual hydrogen bond donors and Br- synergistically promote ring-opening reactions of epoxides, while amide groups serve as basic sites to enhance CO2 adsorption during the reaction process.

The dynamics of the flavin, NADPH, and active site loops determine the mechanism of activation of class B flavin-dependent monooxygenases.

Flavin-dependent monooxygenases (FMOs) constitute a diverse enzyme family that catalyzes crucial hydroxylation, epoxidation, and Baeyer-Villiger reactions across various metabolic pathways in all domains of life. Due to the intricate nature of this enzyme family's mechanisms, some aspects of their functioning remain unknown. Here, we present the results of molecular dynamics computations, supplemented by a bioinformatics analysis, that clarify the early stages of their catalytic cycle. We have elucidated the intricate binding mechanism of NADPH and L-Orn to a class B monooxygenase, the ornithine hydroxylase from known as SidA. Our investigation involved a comprehensive characterization of the conformational changes associated with the FAD (Flavin Adenine Dinucleotide) cofactor, transitioning from the out to the in position. Furthermore, we explored the rotational dynamics of the nicotinamide ring of NADPH, shedding light on its role in facilitating FAD reduction, supported by experimental evidence. Finally, we also analyzed the extent of conservation of two Tyr-loops that play critical roles in the process.

Mechanistic Insights into Urea‐, Thiourea‐, and Isothiourea‐Based Bifunctional Tetraarylphosphonium Salt Catalysis for Conversion of Carbon Dioxide to Cyclic Carbonates

AbstractA novel bifunctional isothiourea derived from a tetraarylphosphonium salt catalyzes the coupling reaction of monosubstituted epoxides with 1 atm of carbon dioxide to afford five‐membered cyclic carbonates in high yields. Thiourea and urea groups are also effective hydrogen bond donors for the carbon dioxide fixation. Comprehensive mechanistic studies on this catalysis using theoretical calculations disclosed key hydrogen bond interactions between catalysts and intermediates, which relied upon orientation of the binding modes.

Preparation of hierarchical TS-1 zeolites from ordered macroporous-mesoporous carbon templates for efficient chloropropene epoxidation

The combination of titanium silicalite-1 (TS-1) zeolite and H2O2 oxidant provides an excellent alternative to many highly toxic and polluting olefin oxidation processes due to the by-product being water-only and without deep oxidation. However, the diffusion of bulky reactants and products suffers from the inherent micropores of conventional TS-1 zeolites. Herein, we designed a reticulated ordered macroporous carbon material with uniform and coherent mesopores, and successfully synthesized ordered hierarchical TS-1 zeolites containing intracrystalline macroporous-mesoporous-microporous by dry gel method. The fully interconnected intracrystalline macroporous-mesoporous-microporous hierarchical TS-1 improves the accessibility of the active site and the diffusion efficiency of bulky compounds. It showed excellent catalytic performance during the epoxidation reaction of chloropropene, and its epichlorohydrin yield and H2O2 effective utilization were 70.11% and 77.05%, which were 2.2 and 1.9 times of the catalytic performance of commercial TS-1 zeolites, respectively, and significantly better than the ultrafine TS-1 synthesized by conventional methods. The high catalytic performance was maintained after three cycles of use. This offers a good opportunity for the design and synthesis of efficient zeolite catalysts in the future.

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.

Zeolite structure descriptor for guiding the synthesis of efficient titanosilicalites through matching Ti sites and framework topologies for 1-Hexene epoxidation

Rational design of metal-containing zeolites with different framework topologies can boost catalytic performance, but the successful synthesis of metal-containing zeolites typically requires selection of suitable zeolite scaffolds. Herein, a zeolite structure descriptor (i.e., the local framework disturbance index, LFDI) is proposed to guide the design of Ti-containing zeolites by matching Ti sites and different framework topologies to enhance olefin epoxidation performance. Theoretical calculations of the incorporation of Ti metal atoms into different crystallographic T sites indicate that the BEA framework exhibits the more negative average substitution energy (-0.50 eV) than MFI and MEL frameworks due to the lowest average LFDI (3.14). As expected, the BEA framework showed the highest capacity of framework Ti species than MFI and MEL frameworks by atom-planting method. This high framework Ti content demonstrated outstanding 1-hexene epoxidation performances (TON: 1827.5). This work paves the way to rationally design Ti-containing zeolites by atom-planting method for epoxidation reactions.

Mechanism of the Sharpless Epoxidation Reaction: A DFT Study.

The Sharpless reaction is an enantioselective epoxidation of prochiral allylic alcohols that employs a Ti(IV) catalyst formed from titanium tetra(isopropoxide), Ti(O-i-Pr)4, diethyl tartrate (DET), and the oxidizing agent tert-butyl hydroperoxide. The M06-2X DFT functional with the 6-311+G(d,p) basis set has been employed to model the structures and energetics of the Sharpless epoxidation reaction. The monomeric tetracoordinate titanium(IV) diethyltartrate is thermodynamically strongly favored to dimerize, producing a pentacoordinate catalyst, [Ti(DET)(O-i-Pr)2]2, that is a more reactive chiral epoxidation catalyst. The rapid ligand exchange reactions needed to generate the "loaded" catalyst and to repeat the overall catalytic cycle have been examined and are found to have activation energies that are much lower than the epoxidation barriers. The transition structures and activation energies for the enantioselective epoxidation of allyl alcohol, trans-methyl-allyl alcohol and trans-tert-butyl-allyl alcohol with the "loaded" Sharpless catalyst, [Ti2(DET)2(O-i-Pr)2-(OAllyl)-(OOt-Bu)], are presented. The effect of the C═O···Ti interactions on the activation energies and the significance of the O-C-C═C dihedral angle on the enantioselectivity of the epoxidation reaction are discussed.

Electrocatalytic epoxidation of cyclooctene to epoxides driven by cobalt-containing polyoxometalate

The electrocatalytic epoxidation directly using water as oxygen source is considered as a sustainable strategy to achieve epoxide production under ambient conditions. However, it is challenging to develop non-noble metal based heterogeneous electrocatalysts for efficient epoxidation with a deep understanding of the structure–activity relationships. In this work, we report a Weakley-polyoxometalate Na10[Co4(H2O)2(PW9O34)2] (Co4P2W18) with high efficiency toward electrocatalytic epoxidation of cyclooctene via directly transfer oxygen atom from water. A significantly higher faradaic efficiency of cyclooctene oxide was achieved over Co4P2W18 than a Keggin type Co substituted polyoxometalate Na5[Co(H2O)PW11O39] (CoPW11) and some other typical electrocatalysts including RuO2, IrO2, and Co3O4 in our system. Experimental results and theoretical calculation indicate that the oxygen atom directly transfers from water for the epoxidation of cyclooctene via the cleavage of O−H of pre-adsorbed water as the rate-determined step. Further calculation demonstrates that the water and cyclooctene were adsorbed by Co site and their adjacent terminal oxygen atom during the epoxidation reaction. With the assistance of this terminal oxygen atom for adsorption and as an electron capture center, lower energy barriers for activation of water and cyclooctene are observed on Co4P2W18 than on CoPW11. Our study provides atomic insight into how structure affects catalytic activity, which benefits designing efficient electrocatalysts.