Ether Formation Research Articles

Theoretical insights into formation of ethylene, propylene and butylene in Co2C (020) catalyzed FTO process

Fischer–Tropsch Synthesis to lower olefins (FTO) is an important non-petroleum route to produce lower olefins. Nanoprisms Co2C has been discovered as a promising FTO catalyst possessing high selectivity to olefins and low CH4 selectivity for its exposing (020) facet. Density Functional Theory (DFT) was used to understand the reason for inhibiting methane formation, the chain growth mechanism and dominant formation pathway of three main low olefins. The results show that the activation energy for CH2* to couple with CH* (0.51 eV) was much lower than that for further hydrogenation to form CH3* (0.66 eV), which was the key species to produce methane. Therefore, the mechanism inhibiting methane formation was Co2C(020) promoting CH2*-CH*coupling rather CH2* hydrogen. Moreover, it can be predict that the carbon chain would not grow too long, because the coupling activation energy for the C1-C1 coupling, C1-C2 coupling, C1-C3 coupling were 0.51 eV, 0.54 eV and 0.69 eV, respectively. At last, it can be predicted that propylene was the easiest to produce, followed by ethylene and butylene, because their barrier energy were 1.58 eV, 1.64 eV and 2.12 eV, respectively.

Sustainable Electrochemical Benzylic C-H Oxidation Using MeOH as an Oxygen Source.

New methods and strategies for the direct oxidation of benzylic C-H bonds are highly desirable, owing to the importance of ketone motifs in significant organic transformations and the synthesis of valuable molecules, including pharmaceuticals, pesticides, and fine chemicals. Herein, we describe an electrochemical benzylic C-H oxidation strategy for the synthesis of ketones using MeOH as an oxygen source. Inexpensive and safe KBr serves as both an electrolyte and a bromide radical precursor in the reaction. This transformation also offers several advantages such as mild conditions, broad functional group tolerance, and operational simplicity. Mechanistic investigations by control experiments, radical scavenging experiments, electron paramagnetic resonance (EPR), kinetic studies, cyclic voltammetry (CV), and in-situ Fourier transform infrared (FTIR) spectroscopy support a pathway involving the formation and transformation of benzyl methyl ether via hydrogen atom transfer (HAT) and single-electron transfer (SET). The practical application of our strategy is highlighted by the successful synthesis of five pharmaceuticals, namely lenperone, melperone, diphenhydramine, cinnarizine, and flunarizine.

Potential of 2-ethylhexyl nitrate (EHN) and di-tert-butyl peroxide (DTBP) to enhance the cetane number of ethanol, a detailed chemical kinetic study

Ethanol is one of the most promising renewable liquid fuels to decarbonize the internal combustion engine due to its high production capacity, reasonable cost and low carbon intensity. At the same time, diesel engines are preferred over other powertrain technologies in most hard-to-electrify applications, such as heavy-duty, off-road, marine and rail. However, ethanol’s properties are not suitable for modern diesel engines with ignitability being the main technical barrier for ethanol compression-ignition combustion. Cetane improvers, such as 2-ethylhexyl nitrate (EHN) or di-tert-butyl peroxide (DTBP) may be a solution to enable diesel-like ethanol combustion, but the potential of those additives to increase the cetane number of ethanol is still unclear.In this investigation, detailed chemical kinetic simulations were performed to better understand the mechanisms by which EHN and DTBP affect the ignition reactivity of ethanol. Sub-models of EHN and DTBP chemistry were merged with a chemical kinetic mechanism for ethanol and validated against experimental data. Rate of production analyses and sensitivity analyses were performed to better understand the reactions and species that control the autoignition of ethanol additized with EHN or DTBP. The formation and accumulation of acetaldehyde from ethanol-derived radicals is the bottleneck for ignition, since the remaining ethanol acts as a sink of the OH radicals required for the decomposition of acetaldehyde. A simple model to predict the derived cetane number of fuel blends is proposed and used to estimate the effectiveness of EHN and DTBP in improving the reactivity of ethanol. EHN works better as an additive as compared to DTBP, as it speeds up the main decomposition reactions of the fuel by providing the necessary OH radicals as compared to CH3 provided by DTBP.

Tunable Regioselective Allylic Alkylation/Iodination of Imidazoheterocycles in Water.

The switchable roles of allylic alcohol and molecular iodine as reagents and catalysts have been demonstrated in the regioselective allylic alkylation and iodination of imidazoheterocycles employing the mixture of allylic alcohol-I2. First, we have explored the catalytic activity of iodine for the allylation of imidazoheterocycles using allylic alcohol in an aqueous medium. The allylation of a library of imidazoheterocycles and other electron-rich heterocycles like indole, pyrazole, 4-hydroxy coumarin, and 6-amino uracil has been achieved by employing this methodology. The efficiency of the I2 catalyst for N-allylation of azoles has also been demonstrated. Next, we have shown that this mixture of allylic alcohol and I2 could be beneficial for the iodination of imidazoheterocycles under room temperature. Mechanistic studies indicate that the activation of allylic alcohol by molecular iodine took place probably through halogen bonding, and NMR studies show that the reaction did not proceed through allylic ether formation.

Catalytic reactivity of Pt sites for non-oxidative coupling of methane (NOCM)

Recently, single atom catalysts have been suggested as stable and non-coking catalysts for non-oxidative coupling of methane (NOCM) to ethylene and higher hydrocarbons. In this work, reaction kinetics coupled with microscopy and spectroscopy technique were used to understand the nature of the Pt single atom active sites under reaction conditions relevant to industrial applications of NOCM. Under NOCM conditions (975C, Space velocity = 30 L hr-1 gcat-1), single atom Pt supported on CeO2 (Pt SAs) and Pt nanoparticles (∼2nm) supported on SiO2 (Pt NPs) show similar ethylene formation rates and show similar gas phase selectivity to major and minor products like ethylene (∼60 %), ethane (∼20 %) and higher hydrocarbons (propylene, butene, etc.), suggesting that the single sites do not offer a superior performance as claimed in the literature. Power rate law reaction orders with respect to methane, ethylene and hydrogen show similar results for the two catalytic systems (nCH4 = 1, nC2H4 = 0 and nH2 = −0.5), indicating a surface-initiated gas phase radical mechanism for NOCM reactions. Transmission electron microscopy (TEM) of the spent samples (CH4 treated at 975C for 3 h) reveals that materials containing Pt (Pt SAs and Pt NPs) are found to sinter to particles approximately 5–7 nm in size, suggesting that the single atoms do not survive NOCM reaction conditions. Ethylene hydrogenation and CO-IR spectroscopy on fresh and spent catalysts suggest loss of surface Pt sites by coking following NOCM. These results shed light on the nature of the active sites during non-oxidative coupling of methane at industrially relevant conditions and motivate further research on catalyst development for this reaction.

Geometry-based cross-linking algorithm for modeling resorcinol resins through united-atom molecular dynamics simulations

The addition-condensation polymerization (ACP) of resorcinol with formaldehyde and the electrochemical polymerization (ECP) of resorcinol were desirable to improve the performances of resins. To achieve computational design, a new geometry-based cross-linking modeling algorithm for three-dimensional (3D) cross-linked network structures of resorcinol resins was developed for molecular dynamics (MD) simulations using a united-atom model. The ACP and ECP of resorcinol were successfully modeled using one algorithm by changing the parameters of the reaction rate constants of methylene, ether, and biphenyl bond formations. Furthermore, reaction judgment was performed under a reaction probability function comprising the Gaussian functions based on the interatomic distance of the reaction candidate atom pairs and interior angles regarding the spatial arrangement of two resorcinol rings. This geometry-based cross-linking algorithm successfully generated strainless 3D cross-linked network structures of the ACP and ECP resorcinol resins without the formation of highly bent unstable structures, such as U-shaped biphenyls. The MD simulation results indicated that the cross-linking of the ACP resin comprising methylene linkages proceeded with a network structure formation mechanism similar to that of phenolic resins, where the cross-linked network structure was determined at the gel point and the reactions after the gel point were to fix and freeze the network structure. For the ECP resins comprising ether and biphenyl linkages, the molar ratio of ether to biphenyl bonds affected the elastic property of the resins, and the incorporation of rigid biphenyl structures into ether-linkage networks increased the elastic modulus. Moreover, an increase in rigidity was observed as a decrease in the Poisson's ratio.

Alkyl sulfonate surfactant mediates electroreduction of carbon dioxide to ethylene or ethanol over hydroxide-derived copper catalysts.

For CO2 electroreduction (CO2ER) to C2 compounds, it is generally accepted that the formation of ethylene and ethanol shares the same intermediate, *HCCOH. The majority of studies have achieved high faradaic efficiency (FE) towards ethylene, but faced challenges to get high ethanol FE. Herein, we present an alkyl sulfonate surfactant (e.g., sodium dodecyl sulfonate, SDS) mediated CO2ER to a C2 product over an in situ generated Cu catalyst (Cu@SDS) from SDS-modified Cu(OH)2. It achieves the CO2ER to ethylene as the sole C2 product at low applied voltages with a FE of 55% at -0.6 V vs. RHE and to ethanol as the main product at potentials ≥0.7 V with a maximum FE of 64% and a total C2 FE of 86% at -0.8 V, with a current density of 231 mA cm-2 in a flow cell. Mechanism investigation indicates that SDS modifies the oxidation state of the in situ formed Cu species in Cu@SDS, thus tuning the catalyst activity for CO2ER and lowering the C-C coupling energy barrier; meanwhile, it tunes the adsorption mode of the *HCCOH intermediates on the catalyst, thus mediating the selectivity of CO2ER towards C2 products.

High photocatalytic yield in the non-oxidative coupling of methane using a Pd-TiO2 nanomembrane gas flow-through reactor.

The photocatalytic non-oxidative coupling of methane (NOCM) is a highly challenging and sustainable reaction to produce H2 and C2+ hydrocarbons under ambient conditions using sunlight. However, there is a lack of knowledge, particularly on how to achieve high photocatalytic yield in continuous-flow reactors. To address this, we have developed a novel flow-through photocatalytic reactor for NOCM as an alternative to the conventionally used batch reactors. Me/TiO2 photocatalysts, where Me = Au, Ag and Pd, are developed, but only those based on Pd are active. Interestingly, the preparation method significantly impacts performance, going from inactive samples (prepared by wet impregnation) to highly active samples (prepared by strong electrostatic adsorption - SEA). These photocatalysts are deposited on a nanomembrane, and the loading effect, which determines productivity, selectivity, and stability, is also analysed. Transient absorption spectroscopy (TAS) analysis reveals the involvement of holes and photoelectrons after charge separation on Pd/TiO2 (SEA) and their interaction with methane in ethane formation, reaching a production rate of about 1000 μmol g-1 h-1 and a selectivity of almost 95% after 5 hours of reaction. Stability tests involving 24 h of continuous irradiation are performed, showing changes in productivity and selectivity to ethane, ethylene and CO2. The effect of a mild oxidative treatment (80 °C) to extend the catalyst's lifetime is also reported.

Regiospecificity of Immobilized Candida antarctica Lipase B (CAL-B) towards 2,3-Diacyl-1-O-alkyl Glyceryl Ether in Ethanol.

Highly pure 2,3-dioleoyl-1-O-alkyl glyceryl ether (DOGE), whose 1-position is a lipase-tolerant ether bond, was chemically synthesized and its detailed regioselectivity and acyl transfer were confirmed. During ethanolysis using immobilized Candida antarctica lipase B (CAL-B) with DOGE as the substrate, monooleoyl-1-O-alkyl glyceryl ethers (MOGEs) and a few 1-alkyl glyceryl ethers were formed upon consumption of the substrate. The structure of MOGE was confirmed using nuclear magnetic resonance spectroscopy and only the isomer of 2-MOGE was formed, indicating that CAL-B has complete α- regiospecificity. During ethanolysis, 3-MOGE was formed via acyl migration. These results indicate that the formation of 1-alkyl glyceryl ethers is not due to the imperfect regiospecificity of CAL-B, but rather due to ethanolysis of the formed 3-MOGE. The ethanolysis rate at the 3-α-position of DOGE was faster and the rate of acyl transfer was slightly slower for chain lengths greater than 14. These results show for the first time that both deacylation at the 3-position and acyl migration from the 2- to 3-position are affected by the structure of 1-position.

Multilevel quantum mechanical calculations show the role of promoter molecules in the dehydration of methanol to dimethyl ether in H-ZSM-5.

Methyl carboxylate esters promote the formation of dimethyl ether (DME) from the dehydration of methanol in H-ZSM-5 zeolite. We employ a multilevel quantum method to explore the possible associative and dissociative mechanisms in the presence, and absence, of six methyl ester promoters. This hybrid method combines density functional theory, with dispersion corrections (DFT-D3), for the full periodic system, with second-order Møller-Plesset perturbation theory (MP2) for small clusters representing the reaction site, and coupled cluster with single, double, and perturbative triple substitution (CCSD(T)) for the reacting molecules. The calculated adsorption enthalpy of methanol, and reaction enthalpies of the dehydration of methanol to DME within H-ZSM-5, agree with experiment to within chemical accuracy (∼4 kJ mol-1). For the promoters, a reaction pathway via an associative mechanism gives lower overall reaction enthalpies and barriers compared to the reaction with methanol only. Each stage of this mechanism is explored and related to experimental data. We provide evidence that suggests the promoter's adsorption to the Brønsted acid site is the most important factor dictating its efficiency.

Hydrodeoxygenation of anisole over SBA-15-supported Ni, Pd, and Pt mono- and bimetallic catalysts: effect of the metal's nature on catalytic activity and selectivity.

Monometallic Ni, Pd and Pt and bimetallic catalysts formed by combinations of the above metals supported on SBA-15 silica were synthesized, characterized and tested in the hydrodeoxygenation reaction of anisole. The objective of the work was to detect the effect of the nature of metals on the activity of the catalysts at different steps of anisole hydrodeoxygenation: hydrogenation of the aromatic ring of anisole and C-O bond cleavage in the intermediate cyclohexyl methyl ether. The support and the catalysts were characterized by N2 physisorption, X-ray diffraction, UV-vis diffuse reflectance spectroscopy, temperature-programmed reduction, scanning electron microscopy-energy dispersive X-ray spectroscopy, transmission electron microscopy and HAADF-STEM. The catalytic activity tests were carried out in a batch reactor at 280 °C and 7.3 MPa pressure. The activity results show that the NiPd/SBA-15 catalyst had the greatest ability for hydrogenation of the aromatic ring of anisole, while its NiPt/SBA-15 analog resulted in better activity for C-O bond hydrogenolysis. The bimetallic NiPt/SBA-15 catalyst showed the best catalytic performance in the HDO of anisole ascribed to the formation of a Ni-Pt alloy. On the other hand, the combination of Pd and Pt metals in the PdPt/SBA-15 catalyst resulted in the formation of bimetallic particles with Pd-rich and Pt-rich domains, showing high selectivity for the formation of the cyclohexyl methyl ether, which can be useful for the hydrogenation of aromatic rings in O-containing reactants with the formation of saturated O-containing products. According to the characterization results (HAADF-STEM), the different catalytic behavior of NiPd/SBA-15, NiPt/SBA-15, and PdPt/SBA-15 catalysts could be attributed to different characteristics of the bimetallic active phases in them.

A comprehensive experimental and kinetic modeling study of methyl tert-butyl ether combustion

A comprehensive understanding of the combustion chemistry of methyl tert‑butyl ether (MTBE) is of key importance in its application as an additive in gasoline fuels. Ignition delay times (IDTs) of MTBE/air mixtures have been measured in both a high-pressure shock tube (HPST) and in a rapid compression machine (RCM) at equivalence ratios of 0.5, 1.0, and 2.0 in air, at pressures of 10 and 30 bar over the temperature range 600 – 1350 K. Species profiles for MTBE oxidation were obtained in a jet-stirred reactor (JSR) at 1 bar, at equivalence ratios of 0.5, 1.0, and 2.0 in the temperature range 700 – 1100 K.A detailed reaction mechanism, comprising 813 species and 4319 reactions, has been developed and predicts well all of the experimental data obtained in this work and also texisitng literature data. Pressure- and temperature-dependent rate constants for the MTBE unimolecular elimination reaction producing isobutene and methanol were calculated using high-level ab-initio calculations. A sensitivity analysis reveals that this elimination reaction is important, and significantly inhibits fuel reactivity at temperatures above 1300 K. At intermediate temperatures (850 – 1300 K), the reaction MTBE + ȮH = TĊ4H8OCH3 + H2O plays a crucial role in promoting the reactivity of MTBE oxidation, whereas the reaction MTBE + ȮH = TC4H9OĊH2 + H2O is the most inhibiting reaction. At low temperatures (600 – 850 K), the isomerization reaction of TC4OCȮ2–1 ⇌ TĊ4OCO2H-2 significantly promotes the reactivity. Conversely, the reaction 2TC4OCȮ2–1 ↔ 2TC4OCȮ-1 + O2 inhibits reactivity the most. The NTC behavior in MTBE oxidation can be explained by the competition between the reactions involving the formation and consumption of cyclic ethers from TĊ4H8OCH3 radicals and the reactions associated with the formation and consumption of carbonyl hydroperoxide species.

Low-temperature ignition and oxidation mechanisms of tetrahydropyran

Cyclic ethers are relevant as next-generation biofuels and are also combustion intermediates that follow directly from unimolecular decomposition of hydroperoxyalkyl radicals. Accordingly, cyclic ether reactions are crucial to understanding low-temperature oxidation for advanced compression-ignition applications in combustion where peroxy radials are central to degenerate chain-branching pathways. Reaction mechanisms relevant to low-temperature ignition of cyclic ethers contain intrinsic complexities due to competing reactions of carbon-centered radicals formed in the initiation step undergoing either ring-opening or reactions with O2. To gain insight into mechanisms describing tetrahydropyran combustion, ignition delay time and speciation measurements were conducted. The present work integrates measurements below 1000 K of ignition delay times and species profiles in rapid compression machine experiments from 5 – 20 bar, spanning several equivalence ratios, with jet-stirred reactor experiments at 1 bar and stoichiometric conditions. The experiments are complemented with the development of the first chemical kinetics mechanism for tetrahydropyran that includes peroxy radical reactions, including O2-addition to tetrahydropyranyl (Ṙ), HOȮ-elimination from tetrahydropyranylperoxy (ROȮ) and hydroperoxytetrahydropyranyl (Q˙OOH), bi-cyclic ether formation, β-scission of Q˙OOH, and ketohydroperoxide formation.Negative-temperature coefficient (NTC) behavior is exhibited in the experiments and is reflected in the model predictions, which were within experimental uncertainty for several conditions. Disparities between the model predictions and experiments were analyzed via sensitivity analysis to identify contributing factors from elementary reactions. The analyses examine the role of ring-opening products of tetrahydropyranyl and hydroperoxytetrahydropyranyl isomers to identify reaction mechanisms that may contribute to model uncertainties. The detection of 66 species in the JSR experiments indicates that tetrahydropyran undergoes complex reaction networks, which includes interconnected reactions of aldehyde radicals and alkyl radicals. Primary radicals pentanal-5-yl and butanal-4-yl are derived from ring-opening reactions of tetrahydropyran-1-yl and undergo subsequent decarbonylation to form alkyl radicals (1-butyl and 1-propyl) that undergo reaction with O2 and may contribute to chain-branching, in addition to pathways involving tetrahydropyran-derived ketohydroperoxides.

Anion-Driven Nanostructuring of Copper Electrodeposits for Tuning the Selectivity of Electrocatalytic CO2 Reduction Reaction

Electrochemical CO2 reduction (ECR) to value-added products is one of the potential ways to utilise CO2 as a feedstock, thereby decreasing its level in the atmosphere as it has harmful repercussions on planet earth. Copper (Cu)-nanostructures have demonstrated a great potential to convert CO2 into valuable higher-end hydrocarbons electrochemically, but with poor selectivity1. Therefore, novel strategies to tune Cu-based electrocatalysts' activity and selectivity toward multi-carbon products, particularly at low overpotential, are highly desirable. At the same time, keeping in mind the growing concerns regarding the environmental impact of the synthetic procedures and atom-economy among chemists, the synthesis methods employing reagents with multiple characteristics are equally essential to ensure minimal use of undesirable and excess reagents. In the present work, we report an atom-economic strategy to tune the physicochemical properties and the electrocatalytic activity of Cu-nanostructures towards ECR. The Cu-nanostructures namely CA, CN, CS and CC were synthesized via pulse electrodeposition from an electrolyte bath containing Cu-precursor salts with varying anions viz. acetate, nitrate, sulphate, and chloride respectively and are investigated for the effect of anions on the physicochemical properties and ECR performance. In the case of Cu electrodeposition process, when the pH is low as in the case of sulphate and acetate ions, electrodeposition is accompanied by hydrogen evolution reaction2 which results in the formation of nondendritic structures as in the case of CS and CA. But the presence of nitrate ions in the electrolyte bath causes nitrate reduction reaction to take place as a side reaction as well, as Cu is a well-known catalyst for nitrate reduction. Thus, this simultaneous redox reaction at the surface of the Cu electrodeposit causes an additional dissolution of the Cu nuclei3. This results in a smoother morphology as seen in CN as the dendrite formation is overridden. The very distinct cubic morphology of CC is due to Chloride ions in the bath.The presence of chloride ions during the electrodeposition of CC samples results in the formation of nanocubes by reducing Cu2+ via the formation of CuCl which is known to exist in cubic form when it precipitates4. The intermediate CuCl then quickly forms Cu2O through an equilibrium reaction in the presence of H2O when the concentration of chloride ions is not so high. The Cu-nanostructures electrodeposited from Cu-chloride demonstrated the best ECR performance with the highest total faradaic efficiency for carbon products and good selectivity for ethylene formation (30% at -0.93V vs RHE). The presence of chloride ions in the electrolyte bath strongly affects the active sites of the Cu deposits as the cubic morphology of CC catalyst exposes large number of Cu (100) faces5. Cu (100) are highly selective towards ethylene formation with very low overpotential due to the lower barrier for Cu-CO* which leads to greater CO coverage favouring CO*-CO* coupling at low bias59. In addition to that the electrochemically active surface area, the higher Cu+ content can be rationalized as the reasons for relatively higher ECR activity of CC.

Diverting Ni‐Catalyzed Direct Benzylic C−H Hydroxylation towards Trifluoroethoxylation

AbstractNickel(II) complexes with the simple N4 donor aminopyridine ligands BPMEN (N,N′‐dimethyl‐N,N′‐bis(2‐pyridylmethyl)‐1,2‐diaminoethane) and TPA (tris(2‐pyridylmethyl)amine) have been demonstrated to perform as efficient catalysts for the regioselective oxygenation of benzylic C−H groups with m‐chloroperoxybenzoic acid under mild conditions (at 20 °C), typically ensuring >90 % substrate conversions within 1 h at 1 mol % catalyst loadings. Unprecedentedly, replacing the commonly used mixed reaction solvent CH3CN/CH2Cl2 with 2,2,2‐trifluoroethanol diverts the selectivity of the above Ni‐based catalyst systems from hydroxylation/ketonization to trifluoroalkoxylation, with the formation of 1‐phenylalkyl 2,2,2‐trifluoroethyl ethers. The use of 2,2,2‐trifluoroethanol ensures high substrate conversion values (up to 97 %), as well as high selectivity for the ether formation (up to 92 %). Preliminary discussion of the reaction mechanism is given based on the catalytic and literature data.

Degradation behavior and ageing mechanism of E-glass fiber reinforced epoxy resin composite pipes under accelerated thermal ageing conditions

In this work, accelerated ageing experiments with circulating air and simulated oilfield water were carried out at 95 °C on aromatic amine-cured GFRP pipes used in oilfield environments, with effective ageing times of 5000 h and 3000 h respectively. The differences in ageing behavior and ageing mechanisms of the GFRP tubes at different times under the two conditions were then analyzed and discussed. The changes in the apparent morphology and microstructure of the samples after thermal ageing were first observed using optical microscopy and scanning electron microscopy, and the results demonstrated that the thermal oxygen environment triggered more drastic color changes and obvious oxidation layers. The resin matrix manifests a large number of nano-scale micropores and modest matrix shrinkage pores in the micron size range, this is accompanied by damage to the fiber cross-section. Hydrothermal ageing causes further dissolution of the surface resin and dissolution of the exposed fibers. ATR-FTIR analysis verifies the increase in CO bonding of the ester group during thermal oxidation and the decreasing strength of the C–O–C and C–H bonds, while the behavior of ageing water absorption and glass fiber hydrolysis is illustrated by changes in the intensity of the –OH and Si–O characteristic bands. NMR hydrogen spectroscopy verified the formation of amides, methyl ethers and carboxylic acids in the thermal oxidation products of epoxy resins. Furthermore, the decay pattern of the circumferential tensile strength indicates that the hydrothermal environment has a more significant effect on the mechanical properties of GFRP pipes, which is attributed to the physical dissolution of the surface resin, significant hydrolytic damage to the surface exposed fibers, and the combined damage to the resin-fiber interfacial bonding by chloride ions in simulated oilfield water.

Syngas Conversion over Co4 Cluster Grafted on HZSM‐5 Zeolite: Mechanistic Insights from DFT Modeling

AbstractWe present a detailed DFT‐based mechanistic investigation of syngas conversion mechanism over Co4 cluster grafted onto HZSM‐5 zeolite, [Co4H], employing a QM/MM embedded cluster approach. Starting from the [Co4H] complex, our results show that a favorable coordination of CO over H2, followed by CO hydrogenation leads to a stable −CH2O complex, [Co4(CH2O)(H)]. Coordination of a second CO molecule to [Co4(CH2O)(H)] complex, followed by CH2−O bond activation, and subsequent removal of CO as CO2 results in the formation of crucial methylene complex [Co4(CH2)(H)], serving as a branching point for the pathways leading to methane, ethene, and ethane. On the pathway to ethene formation, coordination of a third CO molecule to [Co4(CH2)(H)] complex yields the active [Co4(CH2)(CO)(H)] complex, which is 16.0 kcal mol−1 more stable than the methyl complex [Co4(CH3)] on the pathway to methane. From the active species [Co4(CH2)(CO)(H)], we demonstrate that the pathways to both methane and ethene are competing in nature, with the −CH3 hydrogenation barrier, 35.1 kcal mol−1, is lower by only 1.3 kcal mol−1 than the competing C−O bond activation barrier on the pathway to ethene, 36.4 kcal mol−1. However, the significant stability of the active species [Co4(CH2)(CO)(H)] effectively compensates for this minor difference in barriers, ultimately favoring the formation of ethene over methane. Finally, the ethene desorption barrier is 4.1 kcal mol−1 lower than the ethene hydrogenation barrier on the pathway to ethane, indicating the ease of ethene removal from the system. Overall, our DFT study describes that the syngas conversion mechanism catalyzed by [Co4H] system produces ethene selectively via 4CO+2H2→C2H4+2CO2.

Surfactant-Enhanced Formation of Ethylene from Carbon Monoxide Electroreduction on Copper Catalysts

Surfactant-Enhanced Formation of Ethylene from Carbon Monoxide Electroreduction on Copper Catalysts

Lignin based water-soluble fluorescent macromolecular probes for the detection of Fe3+ ion

Lignin is an abundant biomass material in the natural world, its application value and application scope ought to be enlarged. In this work, dealkalized lignin with good water-solubility was used to combine with water-insoluble boron-dipyrromethene (BODIPY) fluorophore to obtain readily water-soluble macromolecular probes. Firstly, a small molecular fluorescent BODIPY probe with two amino groups (-NH2) and another small molecular fluorescent probe with two chlorine groups (-Cl) were synthesized. Secondly, the small-molecular fluorescent probe with two -NH2 groups reacted with carbonyl groups in the lignin by Schiff base formation reaction. Meanwhile, the small-molecular fluorescent probe with two -Cl groups reacted with hydroxyl groups in the lignin by Williamson ether formation reaction. Eventually, two lignin-based fluorescent probes were obtained. The molecular weights of the two probes reached 22.4 kDa and 20.1 kDa. Moreover, these two fluorescent probes were readily soluble in H2O and DMF. Both of the fluorescent macromolecules have good recognition ability for Fe3+, with detection limits of 2.1 × 10−7 mol/L and 1.1 × 10−7 mol/L respectively. Fe3+ interacts with the fluorescent probe, and the imine bond (-CN-) reacts with Fe3+ to cause fluorescence response. The photo-induced electron transfer effect is enhanced, and the photo-induced electron transfer (PET) mechanism causes the fluorescent quenching. This work expands the application scope of lignin as a biomass material and lays a foundation for the development of lignin materials.

Synthesis and cytotoxicity evaluation of retro-inverso analogue of antitumor bicyclic hexapeptide RA-VII

A retro-inverso analogue of antitumor bicyclic hexapeptide RA-VII was designed and synthesized. A cycloisodityrosine unit was synthesized by the intramolecular diphenyl ether formation of Boc-3-borono-d-Tyr(Me)-d-Tyr-OMe mediated by copper(II) acetate and 4-(dimethylamino)pyridine. After the N-methylation, Boc-Ala-OH and the tripeptide segment were sequentially coupled to the N-terminus of the cycloisodityrosine unit, affording a hexapeptide. After removal of the C- and N-terminal protecting groups, the hexapeptide was subjected to macrocyclization using diphenylphosphoryl azide and NaHCO3 in N,N-dimethylformamide to afford a bicyclic hexapeptide analogue. X-ray crystallography and NMR experiments showed that the analogue had different structural features from RA-VII, which were responsible for the lack of cytotoxic activity of the analogue.