Low Bond Dissociation Energy Research Articles

Structure-controlled graphene-encapsulated nickel nanoparticle with tailored work function to steer chemoselective hydrogenation of nitroarenes

In recent years, novel carbon-layer encapsulation strategies have been emerging for the construction of heterogeneous catalysts. However, the mechanism action of thermos-catalytic systems is still unclear. The synergistic effect of metal particle size and carbon layer quantity on catalytic performance has not been reported. The strategy to control the carbon layer quantity and metal particle size is still a big challenge. Here, we proposed a novel idea to design catalysts connecting the performance and the structure via work function. The direct pyrolysis of organometallic coordination polymer is induced to control the carbon layer quantity and metal particle size of the carbon-encapsulated catalyst. The results show that the reduction in the nickel nanoparticle size and the carbon layer quantity were favorable for pumping electrons from the nickel core. There was a corresponding relationship between the work function of the catalyst and its selective hydrogenation performance of halogenated aromatic nitro compounds. With low carbon-halogen bond dissociation energy, a high work function decreased catalytic selectivity. Therefore, the work function can be served as a bridge connecting to the configurational relationship of catalysts.

Potential of derivation of a series of C6–C14 1-alkene skeletal oxidation mechanisms on the basis of reaction rate rules

Olefins, accounting for one-fifth proportion of gasoline fuel, are also essential intermediates in the combustion of large hydrocarbons and vital precursors of large polycyclic aromatic hydrocarbons and soot. The unsaturated C = C bond of alkenes renders a more complex low-temperature reaction scheme compared with their corresponding n-alkanes. Thus, it is of great necessity to obtain a thorough knowledge of the chemical kinetics of alkenes. However, the studies on the chemical kinetics of long-chain olefins are far from sufficient. In this work, a collection of skeletal oxidation mechanisms for 1-alkenes from 1-hexene (C6H12-1) to 1-tetradecene (C14H28-1) were constructed in light of recent advances in skeletal mechanism construction for fuels sharing similar structures based on reaction rate rules. For each 1-alkene, the skeletal mechanism includes ∼54 species and ∼216 reactions. Meanwhile, the effect of the C = C double bond was evaluated by conducting a bond dissociation energy calculation to assist the skeletal mechanism construction and derivation. It is discovered that the allylic position is preferred for H-atom abstraction reactions owing to its lowest bond dissociation energy among different locations for all heavy 1-alkenes. Furthermore, the reactions of OH addition to the C = C bond become important at low temperatures, which competes with the H-atom abstraction reactions. This results in the lower reactivity of 1-alkenes compared with corresponding n-alkanes at low temperatures. The acquired skeletal mechanisms were validated against extensive experimental data including laminar flame speeds, ignition delay times in shock tubes, and key species concentrations in jet-stirred reactors, flow reactors, and premixed laminar flames. The good agreements between experiments and simulations demonstrate the prediction capability of all the skeletal mechanisms of 1-alkenes although minor discrepancies exist in the concentration predictions for C2–C3 species, which might stem from a highly reduced C2–C3 sub-mechanism being utilized in the present mechanism.

Improved Performance of Positive-Ion Mode Free Radical-Initiated Peptide Sequencing with p-TEMPO-Bz.

Free radical-initiated peptide sequencing (FRIPS) is a tandem mass spectrometry technique that generates sequence informative ions via collisionally initiated radical chemistry. Collision activation homolytically cleaves an installed radical precursor and initiates radical formation, extensive hydrogen atom transfer, and peptide backbone dissociation. While the FRIPS technique shows great promise, when applied to multiply charged derivatized peptide ions, a series of high-abundance mass losses are observed which siphon ion abundance from radically generated sequence ions. This loss of ion abundance reduces the sequence coverage generated by FRIPS fragmentation. In this work, we hypothesized that these mass losses were assisted by the ortho-orientation of the radical precursor undergoing facile conversion into five- or six-membered intermediates or products and that when combined with the lower bond dissociation energy of the para-precursor, conjugated peptides would not undergo this chemistry. To test this assertion, we synthesized p-TEMPO-Bz, conjugated it to these peptides, and collisionally activated each. Indeed, we see dramatic attenuation of these undesired collisional processes and a significant increase in radical precursor ion abundance. The increase in ion abundance leads to a significant increase in the sequence coverage generated. These results demonstrate that p-TEMPO-Bz significantly improves the performance of positive-ion mode FRIPS and may be a compelling alternative to the currently utilized o-TEMPO-Bz-based FRIPS.

Reductive gas manipulation at early self-heating stage enables controllable battery thermal failure

<h2>Summary</h2> Li-ion batteries are regarded as unsafe due to the volatility and flammability of the organic liquid electrolytes. However, research on substitutes (solid, inorganic, etc.) still encounters tough obstacles toward commercialization. Here, we manage to control the thermal failure process of liquid batteries by manipulating the deleterious reactions at an earlier stage, where heat accumulates mildly before accelerating to catastrophes. We reveal that the reductive gases, specifically those with low bond dissociation energies (unsaturated hydrocarbons as alkenes and alkynes), can induce cathode crystal change with oxygen release and initiate and accelerate battery thermal failure from lower than 80°C. Four safety countermeasures to break this "reductive attack" pathway are designed and successfully prevent commercial Li-ion batteries from thermal runaway (capacity of 60 Ah and energy density of 280 Wh kg⁻¹). We anticipate that our new safety insights and methodologies will overcome the limitations of liquid electrolytes for safe energy applications.

Experimental and theoretical study on the transformation of typical organic sulfur during hydrothermal carbonization of sludge

This study reports the migration and transformation of sulfur during the hydrothermal carbonization of sludge and two thermal unstable organic-S model compounds (aliphatic-S and aromatic-S) at 150 to 240 °C, focusing on the pathways based on the molecular level. The theoretical calculation indicates that the sulfur atom is the initial attacked position by nucleophile in the organic-S molecule, caused by its maximum contribution (i.e., 73.54 % for aliphatic-S) to the highest occupied molecular orbital (HOMO) and the minimum point of electrostatic potential (ESP, i.e., −103.68 kJ/mol for aliphatic-S). This leads to the nucleophilic addition reaction of aliphatic-S and aromatic-S, especially at 210 °C, along with the generation of sulfoxide-S and sulfone-S. Compared with aromatic-S, the aliphatic-S is more inclined to oxidation because of its higher HOMO contribution and lower ESP. Due to the low bond dissociation energy of CS of formed sulfoxide-S and sulfone-S, large of them (i.e., 47.51 % at 210 °C) transform to SO32- and SO42- ions via desulfurization and oxidation reactions, resulting in a low sulfur content in hydrochar. Also, the sulfoxide-S derived from aliphatic-S is more likely to decompose than other intermediates, together with the aliphatic-S, released as sulfur-containing odorants (especially for H2S, CH3SH and SO2). These findings indicate that fixing the aliphatic-S is an effectively method to control the emission of odorants.

Analysis of chemical bonding of the ground and low-lying states of Mo2 and of Mo2Clx complexes, x = 2-10.

In this study, we perform accurate calculations via multireference configuration interaction and coupled cluster methodologies on the dimolybdenum molecule in conjunction with complete series of correlation and weighted core correlation consistent basis sets up to quintuple size. The bonding, the dissociation energies, and the spectroscopic parameters of the seven states that correlate with the ground state products are calculated. The ground state has a sextuple chemical bond, and each of the calculated excited states has one less bond than the previous state. The calculated values for the ground X1Σg + state of Mo2 have been extrapolated to the complete basis set limits. Our final values, re = 1.9324 Å and De (D0) = 4.502 ± 0.007(4.471 ± 0.009) eV, are in excellent agreement with the experimental values of re = 1.929, 1.938(9) Å and D0 = 4.476(10) eV. Mo2 in the Σg+13 state is a weakly bound dimer, forming 5s⋯5pz bonds, with De = 0.120eV at re = 3.53 Å. All calculated excited states (except Σg+13) have a highly multireference character (C0 = 0.25-0.55). The ordering of the molecular bonding orbitals changes as the spin is increased from quintet to septet state resulting in a change in energy separation ΔS,S-1 of the calculated states. The quite low bond dissociation energy of the ground state is due to the splitting of the molecular bonding orbitals in two groups differing in energy by ∼3eV. Finally, the bond breaking of Mo2, as the multiplicity of spin is increased, is analyzed in parallel with the Mo-Mo bond breaking in a series of Mo2Clx complexes when x is increased. Physical insight into the nature of the sextuple bond and its low dissociation energy is provided.

Melt-state degradation mechanism of poly (ether ketone ketone): the role of branching on crystallization and rheological behavior

In the melt-state, poly (ether ketone ketone) (PEKK) undergoes structural changes to the polymer backbone due to its high melting temperature. In this work, the thermal degradation mechanism of PEKK in the melt-state in air is identified using a combination of molecular dynamics (MD) simulations, X-ray photoelectron spectroscopy (XPS), and rheology. Ether linkages in the PEKK backbone are shown to have the lowest bond dissociation energies and preferentially undergo chain scission compared to ketone linkages. Upon chain scission, the formed radical species undergo hydrogen abstraction, chain transfer, and a coupling reaction, resulting in altered viscoelastic properties. Dynamic rheological behavior of PEKK thermally aged in the melt-state display viscoelastic characteristics of long-chain branched polymers. Results indicate that the PEKK rheological properties are highly dependent on time in the melt-state as well as angular frequency. Increased exposure times in the melt-state result in increased complex viscosity and a reduction in the degree and rate of crystallization. Thermal history has a significant impact on thermomechanical properties in the melt-state and during crystallization.

Selective hydrogenolysis of C-O bonds in lignin and its model compounds over a high-performance Ru/AC catalyst under mild conditions

Selective hydrogenolysis of C-O bonds in lignin is regarded as the most promising strategy to produce high value-added biofuels and chemicals. Herein, Ru/AC catalysts of Ru supported on AC from coal tar pitch were successfully prepared and could effectively promote the cleavage of C-O bonds in diphenyl ether (DPE), benzyl phenyl ether (BPE) and lignin under mild conditions. In the case of an activation ratio of 4:1, the obtained Ru/4-1AC possessed the large specific surface area, more defects, small Ru metal particle size and low Ru0 bonding energy, exhibiting the high catalytic performance. The conversion investigation of the mixture of DPE and BPE revealed that BPE was preferentially adsorbed on Ru metal of the catalyst surface for the C-O bond cleavage due to the lower bond dissociation energy of C-O bonds of BPE and the stronger adsorption energy of BPE calculated by a density functional theory.

Mechanochemical Aliphatic Iodination (and Bromination) by Cascaded Cyclization

AbstractAliphatic iodination via mechanochemistry is a mammoth challenge due to the high polarizability and weak electrophilicity of iodonium cation (I+), and low bond dissociation energy of carbon iodine bond. Herein, the synthesis is demonstrated of oxazoline derivatives from N‐allyl benzamides via mechanochemical cascaded cyclization and halogenation using N‐iodo‐ and N‐bromosuccinimides, respectively, as bifunctional reagents.

Insight into a stepped fragmentation of coal-related model compounds using a tandem Orbitrap mass spectrometer

To provide basic knowledge for coal conversion, twenty one coal-related model compounds (MCs) were analyzed using a tandem Orbitrap mass spectrometer (MS). Higher-energy collisional dissociation (HCD), a method of Orbitrap MS, unraveled the detailed fragmentation pathways and de-alkylation behaviors of the ionized MCs under collision energies from 10 to 80 eV. Chemical bond breaking, hydrogen loss, rearrangement reaction, and elimination of neutral fragments were discussed to elucidate clear fragmentation pathways. For arenes without alkyl chains, a higher energy threshold of fragmentation was observed with the increasing of aromatic ring due to a higher conjugate effect of condensed aromatic structure. The existence of alkyl chains decreased the threshold of fragmentation because of the electron-donating effect of alkyl chains. Heteroatom-containing aromatic compounds, a series of important species in coal, showed a diversified fragmentation patterns due to a low bond dissociation energy and a weak conjugate effect compared with arenes. Fragmentation pathways and de-alkylation behaviors of coal-related MCs will contribute to building monitoring methods for coal and its derivatives conversions in chemical industry.

Effect of Solvent on Antioxidant Activity of Zanthoxylum oxyphyllum Edgew and its DFT Study

Background: Free radicals can easily damage DNA, proteins and lipids within the tissue. Anti-oxidants from natural sources can diminish the actions of free radicals. The current study deals with the chemical composition and antioxidant activity of the leaves of Zanthoxylum oxyphyllum Edgew. Methods: The antioxidant activities for DPPH, FRAP, ABTS radicals, phosphomolybdate assay, reducing power, and chelating power assay were evaluated of ethanol (ET), methanol (ME), chloroform (CH), ethyl acetate (EA), and petroleum ether (PE) extracts of the leaves. The Density Functional Theory (DFT) study was carried out on major identified phytochemicals to evaluate bioactive molecules responsible for the antioxidant activity. Results: It was observed that the ME extract showed the most potent scavenging activity in DPPH, FRAP, ABTS radicals, phosphomolybdate assay, reducing power, and chelating power assay. The phenolic acids and flavonoids like quercetin, gallic acid, sinapic acid, etc. were identified. The DFT study was done for major phytochemicals of ME extract to evaluate the most responsible bioactive molecule for antioxidant activity. The Gallic acid exhibited the lowest bond dissociation energy (BDE) of 314.9 kcal/mol in gas, 309.2 kcal/mol in methanol, respectively, along with the highest value of radical stabilization energy (RSE), 29.5 kcal/mol. Conclusion: Gallic acid was found to be the most responsible antioxidant among the other compounds, and ME the best solvent system for extraction, followed by CH.

A base-controlled switch of SO2 reincorporation in photocatalyzed radical difunctionalization of alkenes

A base-controlled switch of SO2 reincorporation in photocatalyzed radical difunctionalization of alkenes

Mechanochemistry of Group 4 Element-Based Metal-Organic Frameworks.

Mechanochemical synthesis is emerging as an environmentally friendly yet efficient approach to preparing metal-organic frameworks (MOFs). Herein, we report our systematic investigation on the mechanochemical syntheses of Group 4 element-based MOFs. The developed mechanochemistry allows us to synthesize a family of Hf4O4(OH)4(OOC)12-based MOFs. Integrating [Zr6O4(OH)4(OAc)12]2 and [Hf6O4(OH)4(OAc)12]2 under the mechanochemical conditions leads to a unique family of cluster-precise multimetallic MOFs that cannot be accessed by the conventional solvothermal synthesis. Extensive efforts have not yielded an effective pathway for preparing TiIV-derived MOFs, tentatively because of the relatively low Ti-O bond dissociation energy.

NCBSI/KI: A Reagent System for Iodination of Aromatics through In Situ Generation of I-Cl.

In situ iodine monochloride (I-Cl) generation followed by iodination of aromatics using NCBSI/KI system has been developed. The NCBSI reagent requires no activation due to longer bond length, lower bond dissociation energy, and higher absolute charge density on nitrogen. The system is adequate for mono- and diiodination of a wide range of moderate to highly activated arenes with good yield and purity. Moreover, the precursor N-(benzenesulfonyl)benzenesulfonamide can be recovered and transformed to NCBSI, making the protocol eco-friendly and cost-effective.

Electrophotocatalytic Si–H Activation Governed by Polarity-Matching Effects

Electrophotocatalytic Si–H Activation Governed by Polarity-Matching Effects

Novel phenolic compounds by DFT: Electronic effects on antioxidant activity of 4‐vinylphenol derivatives

AbstractConsidering the biological importance of phenolic compounds and their antioxidant activities, we have reached for 10 novel 2,6‐diX‐4‐vinylphenol derivatives (X = NMe2, NH2, OMe, Me, H, Br, Cl, F, CN, and CF3, 1NMe2‐10CF3), at the B3LYP/6‐311++G** level of theory. To evaluate their antioxidant efficiency, the OH bond dissociation energy (BDE) and vertical ionization potential (IPV) are investigated for all structures in gas, water, and benzene phases, using conductor‐like polarized continuum model (CPCM) via B3LYP, LC‐ωPBE, M05‐2X, and M06‐2X functionals. The results indicate that in going from electron‐withdrawing groups (EWGs) to electron‐donating groups (EDGs), the BDE and IPV values decrease which may suggest the increasing efficiency of antioxidants via hydrogen atom transfer (HAT) and single electron transfer (SET) mechanisms, respectively. The calculated rate constants (krxn) for reactions between 1NMe2‐10CF3 with ·OOH and·OH radicals indicate that 1NMe2 shows the highest one. The nucleus‐independent chemical shift (NICS) index, energies of highest occupied and lowest unoccupied molecular orbitals (EHOMO and ELUMO, respectively), and natural bond orbital (NBO) analysis provide relevant results to understand the nature of antioxidant activity and stability of their corresponding radicals. The lowest BDE and IPV values are observed in gas and water phases, respectively. Structure 1NMe2 turns out as the most efficient antioxidant for showing the lowest values of BDE and IPV and highest values of NICS, EHOMO, second‐order perturbation energy (E2) and natural charge. Spin densities and electrostatic potential (ESP) maps appear consistent with the obtained results. The overall order of antioxidant efficiency in gas, water, and benzene phases is 1NMe2 &gt; 2NH2 &gt;3OMe &gt; 4Me &gt; 5H &gt; 6Br &gt; 7Cl &gt; 8F &gt; 9CN &gt; 10CF3.

Exploring gas-sensing characteristics of (CH2OH)2 with controlling the morphology of BiVO4 by adjusting pH of solution

Different morphologies of BiVO4 samples have been successfully fabricated via a facile hydrothermal method. Their morphologies were modulated via altering the pH of solvent. The characterization results reveal that the typical BiVO4-1 is decagonal and BiVO4-6 is coral-like. The gas sensing test results illustrate that the coral-like BiVO4-6 has an excellent gas-sensing response. (The response value reaches 86.49–100 ppm EG at 340 °C) and the sensor still gives an obvious response value (10.21) even upon exposure to 5 ppm EG. The good selectivity toward EG might be due to that EG owns the lowest bond dissociation energy, and the reason for enhancing responses can be the reduction of grain size and the increase of surface area. Thus, all test results illustrate that the coral-like BiVO4-6 is a promising candidate to detect EG.

Diphenyl ditelluride as a low-potential and fast-kinetics anolyte for nonaqueous redox flow battery applications

Developing low-potential, fast-kinetics and highly concentrated anolyte materials is one of the major challenges for nonaqueous redox flow batteries (NRFBs). Organosulfides exhibit promising potentials for NRFBs owing to their high solubility and structure diversity. However, they suffer from poor reaction kinetics and intermediate reversible potential, leading to poor roundtrip efficiency and low full cell voltage. Herein, we report diphenyl ditelluride (PDTe) as a low-potential and fast-kinetics anolyte candidate. The reversible potential of PDTe (average 1.97 V vs. Li/Li+) is lower than that of its sulfur counterpart PDS (2.25 V), which offers higher full cell voltages. We demonstrated a Li/2.5 M PDTe half-cell with a high volumetric capacity (128 Ah L−1PDTe), and high coulombic and energy efficiency (>99.5% and 84.1%) over 100 cycles. A Li/0.1 M PDTe flow cell achieved a stable long cycling over 260 cycles (38 days) at 1.5 mA cm−2. Coupling with lithium iodide (LiI) catholyte, the PDTe/LiI full cells demonstrated stable cycling over 120 cycles. Density functional theory calculation reveals that the cleavage of ditelluride bond requires a much lower bond dissociation energy than that of disulfide bond, which significantly reduces battery voltage hysteresis (by 429 mV). This study demonstrates the promising potential of organotellurides as anolytes for energy storage applications.

Unimolecular Fragmentation Properties of Thermometer Ions from Chemical Dynamics Simulations.

Thermometer ions are widely used to calibrate the internal energy of the ions produced by electrospray ionization in mass spectrometry. Typically, benzylpyridinium ions with different substituents are used. More recently, benzhydrylpyridinium ions were proposed for their lower bond dissociation energies. Direct dynamics simulations using M06-2X/6-31G(d), DFTB, and PM6-D3 are performed to characterize the activation energies of two representative systems: para-methylbenzylpyridinium ion (p-Me-BnPy+) and methyl,methylbenzhydrylpyridinium ion (Me,Me-BhPy+). Simulation results are used to calculate rate constants for the two systems. These rate constants and their uncertainties are used to find the Arrhenius activation energies and RRK fitted threshold energies which give reasonable agreement with calculated bond dissociation energies at the same level of theory. There is only one fragmentation mechanism observed for both systems, which involves C-N bond dissociation via a loose transition state, to generate either benzylium or benzhydrylium ion and a neutral pyridine molecule. For p-Me-BnPy+ using DFTB and PM6-D3 the formation of tropylium ion, from rearrangement of benzylium ion, was observed but only at higher excitation energies and for longer simulation times. These observations suggest that there is no competition between reaction pathways that could affect the reliability of internal energy calibrations. Finally, we suggest using DFTB with a modified-Arrhenius model in future studies.

A kinetic study on pyrolysis of iso-propylcyclohexane: Fuel structure effects of alkylcyclohexane isomers on reaction mechanisms

To reveal insights into the fuel decomposition and combustion mechanisms of alkylcycloalkanes, an intermediate-to-high-temperature pyrolysis investigation of iso-propylcyclohexane (i-PCH) was carried out in a flow reactor at low and atmospheric pressures. The quantitative measurements were accomplished with the aid of synchrotron vacuum ultraviolet photoionization mass spectrometry and the mole fraction profiles of over thirty species were evaluated. A new kinetic model for i-PCH was developed, and the model feasibility was validated by the measured data. Model analyses revealed that the CH3-dissociation reaction is the most sensitive reaction for the destruction of the fuel, and this reaction together with the hydrogen abstractions on active carbon sites takes the dominance of the fuel decomposition. Due to the low bond dissociation energies (BDEs) of the C-C and C-H bonds in the isopropyl group, the primary decomposition temperatures of i-PCH are lower than those of n-propylcyclohexane (n-PCH). Besides, the isopropyl side-chain structure affects many aspects of combustion characteristics of the fuel involving the initial fuel consumption routes and formation of branched species pool, leading to the enhancement of some hexatomic species and inhibition of aromatics production.