Showing papers on "Ether published in 2021"

Elucidating the Mechanism of Fast Na Storage Kinetics in Ether Electrolytes for Hard Carbon Anodes

Abstract: The sodium storage performance of a hard carbon (HC) anode in ether electrolytes exhibits a higher initial Coulombic efficiency (ICE) and better rate performance compared to conventional ester electrolytes. However, the mechanism behind faster Na storage kinetics for HC in ether electrolytes remains unclear. Herein, a unique solvated Na+ and Na+ co-intercalation mechanism in ether electrolytes is reported using designed monodispersed HC nanospheres. In addition, a thin solid electrolyte interphase film with a high inorganic proportion formed in an ether electrolyte is visualized by cryo transmission electron microscopy and depth-profiling X-ray photoelectron spectroscopy, which facilitates Na+ transportation, and results in a high ICE. Furthermore, the fast solvated Na+ diffusion kinetics in ether electrolytes are also revealed via molecular dynamics simulation. Owing to the contribution of the ether electrolytes, an excellent rate performance (214 mAh g-1 at 10 A g-1 with an ultrahigh plateau capacity of 120 mAh g-1 ) and a high ICE (84.93% at 1 A g-1 ) are observed in a half cell; in a full cell, an attractive specific capacity of 110.3 mAh g-1 is achieved after 1000 cycles at 1 A g-1 .

Synthesis of C2+ Chemicals from CO2 and H2 via C-C Bond Formation.

Abstract: ConspectusThe severity of global warming necessitates urgent CO2 mitigation strategies. Notably, CO2 is a cheap, abundant, and renewable carbon resource, and its chemical transformation has attracted great attention from society. Because CO2 is in the highest oxidation state of the C atom, the hydrogenation of CO2 is the basic means of converting it to organic chemicals. With the rapid development of H2 generation by water splitting using electricity from renewable resources, reactions using CO2 and H2 have become increasingly important. In the past few decades, the advances of CO2 hydrogenation have mostly been focused on the synthesis of C1 products, such as CO, formic acid and its derivatives, methanol, and methane. In many cases, the chemicals with two or more carbons (C2+) are more important. However, the synthesis of C2+ chemicals from CO2 and H2 is much more difficult because it involves controlled hydrogenation and simultaneous C-C bond formation. Obviously, investigations on this topic are of great scientific and practical significance. In recent years, we have been targeting this issue and have successfully synthesized the basic C2+ chemicals including carboxylic acids, alcohols, and liquid hydrocarbons, during which we discovered several important new reactions and new reaction pathways. In this Account, we systematically present our work and insights in a broad context with other related reports.1.We discovered a reaction of acetic acid production from methanol, CO2 and H2, which is different from the well-known methanol carbonylation. We also discovered a reaction of C3+ carboxylic acids syntheses using ethers to react with CO2 and H2, which proceeds via olefins as intermediates. Following the new reaction, we realized the synthesis of acetamide by introducing various amines, which may inspire the development of further catalytic schemes for preparing a variety of special chemicals using carbon dioxide as a building block.2.We designed a series of homogeneous catalysts to accelerate the production of C2+ alcohols via CO2 hydrogenation. In the heterogeneously catalyzed CO2 hydrogenation, we discovered the role of water in enhancing the synthesis of C2+ alcohols. We also developed a series of routes for ethanol production using CO2 and H2 to react with some substrates, such as methanol, dimethyl ether, aryl methyl ether, lignin, or paraformaldehyde.3.We designed a catalyst that can directly hydrogenate CO2 to C5+ hydrocarbons at 200 °C, not via the traditional CO or methanol intermediates. We also designed a route to couple homogeneous and heterogeneous catalysis, where exceptional results are achieved at 180 °C.

Catalytic Asymmetric Synthesis of Unprotected β2-Amino Acids

Abstract: We report here a scalable, catalytic one-pot approach to enantiopure and unmodified β2-amino acids. A newly developed confined imidodiphosphorimidate (IDPi) catalyzes a broadly applicable reaction of diverse bis-silyl ketene acetals with a silylated aminomethyl ether, followed by hydrolytic workup, to give free β2-amino acids in high yields, purity, and enantioselectivity. Importantly, both aromatic and aliphatic β2-amino acids can be obtained using this method. Mechanistic studies are consistent with the aminomethylation to proceed via silylium-based asymmetric counteranion-directed catalysis (Si-ACDC) and a transition state to explain the enantioselectivity is suggested on the basis of density functional theory calculation.

Mechanism of Deep Eutectic Solvent Delignification: Insights from Molecular Dynamics Simulations

Abstract: Based on the field of ReaxFF, the pretreatment of a lignin–carbohydrate complex model in a choline chloride-based deep eutectic solvent was proposed. The results showed that the β-O-4 ether and glycosidic bonds in the model were broken at an optimal temperature of 373 K. The best pretreatment solvent was choline chloride/lactic acid (1:2), and 40% of the model compounds were decomposed. Free protons in deep eutectic solvents were one of the critical factors in the process of biomass delignification, and thus acidic hydrogen binding donors generally had a high lignin removal rate, but there was no significant correlation with the acidity of the hydrogen bonding donors. In the deep eutectic solvents of choline chloride/lactic acid, the delignification effect tended to decrease with the increase of lactic acid content. The delignification effect of monocarboxylic acid hydrogen bond donors decreased with the increasing molecular chain length, while the opposite effect of delignification was observed for dicarboxylic acids. The molecular dynamics simulations showed that choline chloride/glycerol (1:2) with a slightly weaker hydrogen bonding network could bind better and solubilize the product molecules, with interaction energies of −170.89 and −61.99 kJ/mol with carbohydrates and phenolic compounds, respectively.

Side-Chain-Type Anion Exchange Membranes Based on Poly(arylene ether sulfone)s Containing High-Density Quaternary Ammonium Groups.

Abstract: To obtain anion exchange membranes with both high ionic conductivity and good dimensional stability, a series of side-chain-type poly(arylene ether sulfone)s (PAES-QDTPM-x) were designed and synthesized. Quaternary ammonium (QA) groups were densely aggregated and grafted onto the main chain via flexible hydrophobic spacers. Well-defined microphase separation was confirmed by small-angle X-ray scattering. PAES-QDTPM-0.30 exhibited reasonably high conductivity (39.4 mS cm-1 at 20 °C and 76.1 mS cm-1 at 80 °C) and excellent dimensional stability at 80 °C (11.9% in length, 11.2% in thickness) due to the concentration of ion clusters and the side-chain-type structure. All membranes maintained over 82% of the conductivity after alkali treatment for 14 days. In the H2/O2 fuel cell performance test, the maximum power density of PAES-QDTPM-0.30 at 60 °C was 225.8 mW cm-2.

Monoterpenes etherification reactions with alkyl alcohols over cesium partially exchanged Keggin heteropoly salts: effects of catalyst composition

Abstract: In this work, cesium partially exchanged Keggin heteropolyacid (HPA) salts were prepared, characterized, and evaluated as solid catalysts in monoterpenes etherification reactions with alkyl alcohols. A comparison of the activity of soluble HPAs and their insoluble cesium salts showed that among three different Keggin anions the phosphotungstate was the most efficient catalyst. Assessments on the effects of the level of the protons exchange by cesium cations demonstrated that Cs2.5H0.5PW12O40 solid salt was the most active and selective phosphotungstate catalyst, converting β-pinene to α-terpinyl methyl ether. The influences of the main reaction parameters such as reaction temperature, time, catalyst load, substrate nature (i.e., alcohols and monoterpenes) were investigated. We have demonstrated that the simultaneous presence of the cesium ions and protons in the catalyst plays an essential role, being the 2.5–0.5 the optimum molar ratio. The Cs2.5H0.5PW12O40 salt was efficiently recovered and reused without loss of catalytic activity.

Oxidation of di-n-propyl ether: Characterization of low-temperature products

Abstract: The oxidation of di-n-propyl-ether (DPE) was performed in a jet-stirred reactor at 1 and 10 atm, at residence times of 1 and 0.7 s, respectively, and initial fuel concentrations of 5000 and 1000 ppm at 1 and 10 atm, respectively. Atmospheric pressure experiments were used for characterization of cool flame products. The 10 atm experiment provided KHPs profile vs. temperature and mole fraction profiles of stable species which were obtained through sonic probe sampling, gas chromatography, Fourier transform infrared spectrometry analyses. High resolution mass spectrometry analyses (HRMS) with syringe direct injection or ultra-high-pressure liquid chromatography coupling was used to characterize hydroperoxides (C3H8O2, C6H14O3), diols (C6H14O3), ketohydroperoxides (C6H12O4), carboxylic acids, and highly oxygenated molecules (C6H12O6, C6H12O8) resulting from up to four O2 additions on fuel's radicals. Heated electrospray and atmospheric pressure chemical ionizations (HESI and APCI) were used in positive and negative mode. Whereas the CH2 groups neighboring the ether function are the most favorable sites for H-atom abstraction reactions, speciation indicated that other sites can react by metathesis forming a large pool of intermediates. Our kinetic reaction mechanism represents the experimental data for most of the stable species but need to be expended for simulating the formation of newly detected species.

Long-term durable anion exchange membranes based on imidazole-functionalized poly(ether ether ketone) incorporating cationic metal-organic framework

Abstract: In this work, poly (ether ether ketone) (PEEK) was synthesized by direct polycondensation reaction. Subsequently, PEEK was functionalized by 1-vinylimidazole to prepare the polymer matrix (Im-PEEK). Cationic UiO-66-NH2 metal-organic frameworks (C-MOF) was synthesized as fillers. The structure of the C-MOF and the morphology of the membranes were verified by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). The prepared hybrid membranes exhibited excellent alkali stability, among which Im-PEEK/C-MOF-1% could retain 89.2% of the conductivity compare to the original sample membrane after immersing in 1 mol L-1 NaOH solution for 320 h at 60 °C. In addition, the ionic conductivity of Im-PEEK/C-MOF-1% was 73 mS cm-1 at 80 °C, which was higher than that of pure Im-PEEK under the same condition (44.3 mS cm-1 at 80 oC). The results showed that the hybrid membranes have great potential for application in the field of anion exchange membranes.

The Anionic Pathway in the Nickel-Catalysed Cross-Coupling of Aryl Ethers

Abstract: The Ni-catalysed cross-coupling of aryl ethers is a powerful method to forge new C-C and C-heteroatom bonds. However, the inert C(sp2 )-O bond means that a canonical mechanism that relies on the oxidative addition of the aryl ether to a Ni0 centre is thermodynamically and kinetically unfavourable, which suggests that alternative mechanisms may be involved. Here, we provide spectroscopic and structural insights into the anionic pathway, which relies on the formation of electron-rich hetero-bimetallic nickelates by adding organometallic nucleophiles to a Ni0 centre. Assessing the rich co-complexation chemistry between Ni(COD)2 and PhLi has led to the structures and solution-state chemistry of a diverse family of catalytically competent lithium nickelates being unveiled. In addition, we demonstrate dramatic solvent and donor effects, which suggest that the cooperative activation of the aryl ether substrate by Ni0 -ate complexes plays a key role in the catalytic cycle.

Photoswitchable Chiral Phase Transfer Catalyst

Abstract: Azo-crown ether-based photoswitching chiral phase transfer catalysts have been developed to control the catalytic activity by photoirradiation. Azobenzene binaphthyl crown ether (ABCE) can switch i...