Showing papers on "Disproportionation published in 2023"

Spontaneous Reduction of Transition Metal Ions by One Electron in Water Microdroplets and the Atmospheric Implications.

Abstract: Freshman chemistry teaches that Fe3+ and Cu2+ ions are stable in water solutions, but their reduced forms, Fe2+ and Cu+, cannot exist in water as the major oxidation state due to the fast oxidation by O2 and/or disproportionation. Contrary to these well-known facts, significant fractions of dissolved Fe and Cu species exist in their reduced oxidation states in atmospheric water such as deliquesced aerosols, clouds, and fog droplets. Current knowledge attributes these phenomena to the stabilization of the lower oxidation states by the complexation of ligands and the various photochemical or thermal pathways that can reduce the higher oxidation states. In this study, by spraying the water solutions of transition metal ions into microdroplets, we show the results of the spontaneous reduction of ligated Fe(III) and Cu(II) species into Fe(II) and Cu(I) species, presenting a previously unknown source of reduced transition metal ions in atmospheric water. It is the spontaneously generated electrons in water microdroplets that are responsible for the reduction. Control experiments in the atmosphere and in a glove box filled with precisely controlled gaseous contents reveal that O2, CO2, and NO2 are the major competitors for the electrons, forming O2-, HCO2-, and NO2-, respectively. Taking these findings together, we opine that microdroplet chemistry might play significant but previously underestimated roles in atmospheric redox chemistry.

Electrocatalytic Disproportionation of Nitric Oxide Toward Efficient Nitrogen Fixation

Abstract: Electrocatalytic conversion of waste nitric oxide into ammonia is a promising approach to achieve sustainable nitrogen fixation. Herein, a CoNi co‐oxides catalyst is designed for NH3 electrosynthesis with the merits of facilitating NO adsorption and reducing the reaction energy barrier. By synergistic coupling with anodic NO oxidation, electrocatalytic disproportionation of NO is first realized to simultaneously synthesize value‐added double nitrogen products (NH3 and nitrate) with increased total energy efficiency. Furthermore, decoupled acid–base asymmetric electrolyte design is proposed in a united assembled electrolyzer, enabling a high NH3 production rate (26.27 mg h−1 cm−2) with unit faradaic efficiency and a remarkable nitrate production rate of 68.41 mg h−1 cm−2 at the anode. A low cell voltage of 3.58 V is obtained by optimizing ion agglomeration within the membrane to promote the charge‐ion exchange and electrode kinetics. Technoeconomic analysis demonstrates the economic feasibility of recycling waste NO by the electrocatalytic disproportionation strategy.

A Static Tin-Manganese Battery with 30000-Cycle Lifespan Based on Stabilized Mn3+/Mn2+ Redox Chemistry.

Abstract: High-potential Mn3+/Mn2+ redox couple (>1.3 V vs SHE) in a static battery system is rarely reported due to the shuttle and disproportionation of Mn3+ in aqueous solutions. Herein, based on reversible stripping/plating of the Sn anode and stabilized Mn2+/Mn3+ redox couple in the cathode, an aqueous Sn-Mn full battery is established in acidic electrolytes. Sn anode exhibits high deposition efficiency, low polarization, and excellent stability in acidic electrolytes. With the help of H+ and a complexing agent, a reversible conversion between Mn2+ and Mn3+ ions takes place on the graphite surface. Pyrophosphate ligand is initially employed to form a protective layer through a complexation process with Sn4+ on the electrode surface, effectively preventing Mn3+ from disproportionation and hindering the uncontrollable diffusion of Mn3+ to electrolytes. Benefiting from the rational design, the full battery delivers satisfied electrochemical performance including a large capacity (0.45 mAh cm-2 at 5 mA cm-2), high discharge plateau voltage (>1.6 V), excellent rate capability (58% retention from 5 to 30 mA cm-2), and superior cycling stability (no decay after 30 000 cycles). The battery design strategy realizes a robustly stable Mn3+/Mn2+ redox reaction, which broadens research into ultrafast acidic battery systems.

A Long-Lived Water-Soluble Phenazine Radical Cation.

Abstract: Long-lived water-soluble organic radical species have long been desired for applications in bioimaging and aqueous energy storage technologies. In the present work, we report a phenazine radical cation sodium 3,3'-(phenazine-5,10-diyl)bis(propane-1-sulfonate) (PSPR) with a high solubility of 1.4 M and high stability in water. Collaboratively demonstrated by experiments and theoretical calculations, PSPR is not prone to undergo dimerization or disproportionation reactions, and its appropriate electron density avoids reactions with oxygen or water, which contribute together to its long lifetime in water under air. With an open-shell configuration, PSPR shows interesting magnetic activity with a narrow linewidth in the electron paramagnetic resonance spectra and a magnetic circular dichroism response. PSPR exhibits an ambipolar redox activity in water. By pairing with a cheap zinc negative electrolyte, a high-performance aqueous organic redox flow battery based on PSPR as a positive electrolyte with an open-circuit voltage of 1.0 V is established, which shows no obvious capacity fade after cycling for 2500 cycles (∼27 days), demonstrating the great promise of PSPR for large-scale energy-storage technology.

NMR in operando monitoring of mechanochemically accelerated sublimations

Abstract: •NMR spectroscopy is used to monitor mechanochemically accelerated transformations •Naturally occurring self-disproportionation phenomena are resolved and quantified •A mechanically promoted solid-solid chiral recognition is analyzed in operando Solid-solid interactions in optically active materials lead to the phenomena of spontaneous enantioenrichment, with implications in prebiotic chemistry and materials purification. Herein, we report a setup that uses mechanochemistry to promote these interactions and which is coupled with the analytical power of nuclear magnetic resonance (NMR) to in operando monitor the resulting variation. The system is applied to the analysis of optically active species responding to cases of self-disproportionation of enantiomers (SDE) by sublimation. The fundamentals behind the observed phenomenon led to an advanced concept of enantiomers recognition based on selective sublimation. The work shows how mechanochemistry aids the acceleration of the naturally occurring phenomena and how the mechanical promotion of solvent-free solid interactions leads to a simultaneous control over the physicochemical properties of a material. In parallel, the study expands the field of monitoring in mechanochemistry by introducing the concept of continuous transfer and analysis of analytes outside the milling environment. Solid-solid interactions in optically active materials lead to the phenomena of spontaneous enantioenrichment, with implications in prebiotic chemistry and materials purification. Herein, we report a setup that uses mechanochemistry to promote these interactions and which is coupled with the analytical power of nuclear magnetic resonance (NMR) to in operando monitor the resulting variation. The system is applied to the analysis of optically active species responding to cases of self-disproportionation of enantiomers (SDE) by sublimation. The fundamentals behind the observed phenomenon led to an advanced concept of enantiomers recognition based on selective sublimation. The work shows how mechanochemistry aids the acceleration of the naturally occurring phenomena and how the mechanical promotion of solvent-free solid interactions leads to a simultaneous control over the physicochemical properties of a material. In parallel, the study expands the field of monitoring in mechanochemistry by introducing the concept of continuous transfer and analysis of analytes outside the milling environment.

Honeycomb ZrCo Intermetallic for High Performance Hydrogen and Hydrogen Isotope Storage

Abstract: Hydrogen isotope storage materials are of great significance for controlled nuclear fusion, which is promising to provide unlimited clean and dense energy. Conventional storage materials of micrometer-sized polycrystalline ZrCo alloys prepared by the smelting method suffer from slow kinetics, pulverization, disproportionation, and poor cycling stability. Here, we synthesize a honeycomb-structured ZrCo composed of highly crystalline submicrometer ZrCo units using electrospray deposition and magnesiothermic reduction. Compared with conventional ones, honeycomb ZrCo does not require activation and exhibits more than 1 order of magnitude increase in kinetic property. Owing to low defects and low stress, the anti-disproportionation ability and cycling stability of honeycomb ZrCo are also obviously higher than those of conventional ZrCo. Moreover, the interfacial stress (due to hydrogenation/dehydrogenation) as a function of particle radius is established, quantitatively elucidating that small-sized ZrCo reduces stress and pulverization. This study points out a direction for the structural design of ZrCo alloy with high-performance hydrogen isotope storage.

Direct monitoring of Li2S2 evolution and its influence on the reversible capacities of lithium-sulfur battery.

Abstract: The dissolution of polysulfides and the low conductivity of lithium sulfides (Li2S) are generally considered the main reasons for limiting the reversible capacity of the lithium-sulfur (Li-S) system. Nevertheless, as the inevitable intermediate between polysulfides and Li2S, lithium disulfide (Li2S2) evolutions are always overlooked. Herein, the Li2S2 evolutions are monitored based on operando spectra on the pouch cell level for the first time. Experimental results indicate that the Li2S2 undergoes sluggish electrochemical reduction and chemical disproportionation simultaneously during the discharging process, leading to further polysulfide dissolution and Li2S generation without capacity distribution. Besides, compared with the fully oxidized Li2S, Li2S2 still residues at the end of the charging state. As a result, instead of the generally considered Li2S and polysulfides, the sluggish electrochemical conversions and side chemical reactions of Li2S2 are the determining factors in limiting the actual sulfur utilization, corresponding to the poor reversible capacity of a Li-S battery.

Catalytic effect of DMSO in metal‐catalyzed radical polymerization mediated by disproportionation facilitates living and immortal radical polymerizations

Abstract: DMSO, an interesting solvent for copper-catalyzed living radical polymerization (LRP) mediated by disproportionation, does not exhibit the greatest disproportionation of Cu(I)X into Cu(0) and Cu(II)X2. Under suitable conditions, DMSO provides 100% conversion and absence of termination, facilitating the development of complex-architecture methodologies by living and immortal polymerizations. The mechanism yielding this level of precision is being investigated. Here we compare Cu(0)-wire-catalyzed LRP of methyl acrylate mediated by disproportionating ligands tris(2-dimethylaminoethyl)amine, Me6-TREN, tris(2-aminoethyl)amine, TREN, and Me6-TREN/TREN = 1/1 in presence of eight disproportionating solvents, some more efficient than DMSO in disproportionation. Unexpectedly, we observed that all solvents increased the rate of polymerization when monomer concentration decreased. This reversed trend from that of conventional LRPs demonstrates catalytic effect for disproportionating solvents. Above a certain concentration, the classic concentration-rate dependence was observed. The external order of reaction of the apparent rate constant of propagation, kpapp on solvent concentration demonstrated the highest order of reaction for the least disproportionating DMSO. Of all solvents investigated, DMSO has the highest ability to stabilize Cu(0) nanoparticles and therefore, yields the highest activity of Cu(0) nanoparticles rather than their greatest concentration. The implications of the catalytic effect of solvent in this and other reactions were discussed.

Freestanding Mo3N2 nanotubes for long‐term stabilized 2e− intermediate‐based high energy efficiency Li–CO2 batteries

Abstract: Li–CO2 batteries are considered one of the promising power sources owing to ultrahigh energy density and carbon fixation. Nevertheless, the sluggish reaction kinetics of 4e− discharged process (Li2CO3) impede its potential application. One of the efficient strategies for developing cathode catalysts is to stabilize 2e− intermediate Li2C2O4 and improve reaction reversibility. However, long‐term catalysts of stabilized Li2C2O4 are barely achieved, whereas cycle stability is far from satisfactory level. Herein, non‐noble metal–based Mo3N2 is synthesized and employed as freestanding cathodes for Li–CO2 batteries. Owing to rich delocalized electrons of Mo2+ and reversible electron localization structure, freestanding Mo3N2 cathodes exhibit a low charge potential (3.28 V) with an ultralow potential gap (0.64 V), high energy efficiency of up to 80.46%, fast rate capability, and outstanding cycle stability (>910 h). In situ experiments and theoretical calculation verify that Mo3N2 stabilizes 2e− Li2C2O4 intermediate by the interaction of Mo2+ as active sites where Mo2+ promotes the transfer of outer electrons to O, prevents its disproportionation to Li2CO3, and promotes reaction kinetics, contributing to high energy efficiency and outstanding cycle reversibility. In addition, the pouch‐cells deliver ultrahigh energy density of up to 6350.7 W h kg−1 based on the mass of cathode materials.

High-Temperature Conversion of Olefins to Liquid Hydrocarbons on γ-Al2O3

Abstract: Noncatalytic thermal conversion of light olefins proceeds at industrially relevant rates at temperatures above 450 °C and pressures above 50 bar. The discovery of solid acid oligomerization catalysts permitted the use of milder conditions (<300 °C) and significantly improved the octane rating. However, Brønsted acid catalysts deactivate and must be regenerated frequently. In this study, at reaction temperatures of about 250–450 °C and pressures of 1 to 40 bar, olefins react on γ-alumina to form higher molecular weight products. The rate of propylene is about ten times higher than that of ethylene. The products, however, are not a simple olefin oligomerization distribution, and many nonoligomer products are formed. The primary products undergo secondary reactions, including double bond isomerization and H-transfer, giving moderate selectivities for saturated products. Depending on the conversion, temperature, and pressure, the rate of ethylene conversion on alumina is more than 100 times that of thermal, noncatalytic conversion. The apparent activation energy for ethylene conversion is 55–75 kJ/mol, which is much lower than ∼244 kJ/mol observed for the thermal gas-phase reaction. On alumina, some reactants and products undergo disproportionation reactions. For example, propylene forms equal molar amounts of ethylene and iso-butene even at very low conversions. Lewis acid sites on γ-alumina have previously been proposed as the active site for double bond isomerization and H–D exchange. Thus, it seems likely that Lewis acid sites are also catalytic for olefin oligomerization and disproportionation reactions. With the γ-alumina catalyst, high liquid yields can be achieved with little formation of coke and minimal deactivation for at least several days.

The Role of Glyoxal as an Intermediate in the Electrochemical CO2 Reduction Reaction on Copper

Abstract: The C2 product formation mechanism in the electrochemical reduction reaction of CO2 (CO2RR) is still poorly understood. This work aims to analyze the copper-catalyzed electroreduction of aqueous glyoxal to understand its role as a potential reaction intermediate during CO2RR. Multiple reaction pathways are observed during glyoxal reduction, including its electroreduction to ethanol and ethylene glycol, disproportionation to glycolate and formate, and further coupling toward the formation of C4 compounds and graphitic carbon. A significantly high ethylene glycol to ethanol ratio indicates that glyoxal may not be the main intermediate toward ethanol production in CO2RR on Cu, contradicting previous hypotheses. Density functional theory calculations show that the hydration of aldehyde functional groups can shift the ethylene glycol vs ethanol selectivity, in which the former is preferred when the carbonyl groups remain unhydrated. A CO2-to-glycolate pathway is also possible as a consequence of the base-catalyzed internal Cannizzaro disproportionation of glyoxal. Finally, C–C coupling during glyoxal reduction may open up a CO2RR pathway toward C4 products such as tetroses and 1,4-butanediol that have not been previously observed in electrochemical CO2RR. The formation of graphitic carbon also suggests that the carbon deposits usually observed during CO2RR may originate from glyoxal-derived C–C coupling. Our findings offer valuable insights onto the glyoxal pathway of CO2RR and the various multicarbon products that result from the further conversion of glyoxal.

Reductive Coupling of Nitric Oxide by Cu(I): Stepwise Formation of Mono- and Dinitrosyl Species En Route to a Cupric Hyponitrite Intermediate.

Abstract: Transition-metal-mediated reductive coupling of nitric oxide (NO(g)) to nitrous oxide (N2O(g)) has significance across the fields of industrial chemistry, biochemistry, medicine, and environmental health. Herein, we elucidate a density functional theory (DFT)-supplemented mechanism of NO(g) reductive coupling at a copper-ion center, [(tmpa)CuI(MeCN)]+ (1) {tmpa = tris(2-pyridylmethyl)amine}. At -110 °C in EtOH (<-90 °C in MeOH), exposing 1 to NO(g) leads to a new binuclear hyponitrite intermediate [{(tmpa)CuII}2(μ-N2O22-)]2+ (2), exhibiting temperature-dependent irreversible isomerization to the previously characterized κ2-O,O'-trans-[(tmpa)2Cu2II(μ-N2O22-)]2+ (OOXray) complex. Complementary stopped-flow kinetic analysis of the reaction in MeOH reveals an initial mononitrosyl species [(tmpa)Cu(NO)]+ (1-(NO)) that binds a second NO molecule, forming a dinitrosyl species [(tmpa)CuII(NO)2] (1-(NO)2). The decay of 1-(NO)2 requires an available starting complex 1 to form a dicopper-dinitrosyl species hypothesized to be [{(tmpa)Cu}2(μ-NO)2]2+ (D) bearing a diamond-core motif, en route to the formation of hyponitrite intermediate 2. In contrast, exposing 1 to NO(g) in 2-MeTHF/THF (v/v 4:1) at <-80 °C leads to the newly observed transient metastable dinitrosyl species [(tmpa)CuII(NO)2] (1-(NO)2) prior to its disproportionation-mediated transformation to the nitrite product [(tmpa)CuII(NO2)]+. Our study furnishes a near-complete profile of NO(g) activation at a reduced Cu site with tripodal tetradentate ligation in two distinctly different solvents, aided by detailed spectroscopic characterization of metastable intermediates, including resonance Raman characterization of the new dinitrosyl and hyponitrite species detected.

DFT study on the catalytic decomposition of hydrogen peroxide by iron complexes of nitrilotriacetate.

Abstract: The Fenton system in the presence of nitrilotriacetate (NTA) ligand is studied by DFT approach. The calculations show that complexation of Fe(II) with NTA significantly facilitates the H2 O2 activation. The ferric-hydroperoxo intermediate NTAFe(III)OOH predominantly decays via the disproportionation into NTAFe(II)OH2 and NTAFe(IV)O involving the formation of a μ-1,2-hydroperoxo-bridged biferric intermediate. In this mechanism, the bridged hydroperoxo is reduced by hydroperoxo ligand rather than by Fe(III). On the one hand, the NTAFe(III)OOH is sluggish to undergo hydrogen abstraction; on the other hand, it is a good nucleophile that may perform aldehyde deformylation. The present calculations suggest that both ˙OH and Fe(IV)O are generated in the NTA-assisted Fenton system. However, the polycarboxylate ligand provides a favorable environment for H2 O2 to accumulate around iron ion through hydrogen bonding. This promotes the quenching of Fe(IV)O by H2 O2 , rationalizing why the Fe(IV)O species is hardly detected in the NTA-assisted Fenton system.

Catalytic conversion of model compounds of plastic pyrolysis oil over ZSM-5

Abstract: Mechanistic investigation of the catalytic conversion of model compounds for plastic pyrolysis oil (1-octene, octadiene, octane, and toluene) over ZSM-5 in a fixed-bed reactor was studied. 1-Octene breaks down into smaller olefins, which undergo further cracking, oligomerization, cyclization, and hydrogen transfer to eventually produce benzene, toluene, xylene (BTX), coke, and hydrogen. The effect of contact time on 1-octene conversion was further investigated and compared with thermodynamics analyses to elucidate the reaction network. Under the reaction conditions (500 °C, 1 atm), octadiene undergoes thermal coking, significantly contributing to reactor fouling. The products from octane cracking are similar to the products from 1-octene conversion whereas toluene undergoes disproportionation, dealkylation and coking. The analysis of spent catalyst showed long-chain hydrocarbons created by oligomerization reactions filled the pores and covered the surface of the catalyst. When mesoporous ZSM-5 is used instead of conventional, product selectivity is maintained for 70 h in time-on-stream experiments.

Suppressing Disproportionation Decomposition in Sn-Based Perovskite Light-Emitting Diodes

Abstract: Nontoxic Sn-based perovskite light-emitting diodes (Pero-LEDs) have been developing rapidly in recent years. However, high-quality Sn-based perovskite films are hardly prepared because of the heavy self-doping of Sn4+ in the as-prepared films. Most previous reports indicate that the Sn4+ formation is mainly attributed to the Sn2+ oxidation by external oxidizers. Here, for the first time, we reveal that the disproportionation decomposition of Sn2+ during the annealing process plays a critical role in degrading device performance. To resolve this issue, we introduced formamidine thiocyanate into the perovskite precursor as a thermal-sacrificial agent to alleviate the disproportionation decomposition. Finally, we achieved efficient Pero-LEDs with a maximum external quantum efficiency of 5.3% and ultralow efficiency roll-off. This work provides a view of understanding the instability of Sn-based perovskite and presents a practical method to achieve efficient Sn-based Pero-LEDs by suppressing the disproportionation decomposition of Sn2+.

Probing the reactivity of 2,2-diphenyl-1-picrylhydrazyl (DPPH) with metal cations and acids in acetonitrile by electrochemistry and UV-Vis spectroscopy.

Abstract: 2,2-Diphenyl-1-picrylhydrazyl (DPPH) is certainly one of the most widely used free radicals in several applications, because of its high stability. Unfortunately, there are few works dealing with its stability in the presence of many chemical species that coexist during chemical processes. In this work, the stability of DPPH was investigated by electrochemistry and UV-Vis spectroscopy in the presence of some metal cations (Cu2+ and Zn2+) and acids (HClO4 and HNO3) in acetonitrile. In the presence of Cu2+, DPPH was oxidized to DPPH+ with the formation of an equivalent amount of Cu+. With Zn2+, DPPH undergoes a slow disproportionation with the formation of Zn(DPPH)+ and DPPH+, certainly favored by the acidity of the metal cation. This hypothesis was subsequently confirmed by studying the stability of DPPH in the presence of HClO4. This acid of appreciable strength in acetonitrile (pKa = 1.83) causes a fast disproportionation of DPPH with the formation of DPPH-H and DPPH+. This mechanism was confirmed both by UV-Vis spectroscopy and by electrochemistry, with a stoichiometry corresponding to 2 equivalents of DPPH for about 1 equivalent of HClO4. In the presence of nitric acid, which is about 107 weaker than HClO4 in acetonitrile, the disproportionation was much slower. These preliminary results are proof that many chemical species are likely to react with DPPH and indirectly induce sources of bias during its application, especially when evaluating antioxidant properties.

Review on the Parameters of Recycling NdFeB Magnets via a Hydrogenation Process

Abstract: Regarding the restrictions recently imposed by China on the export of rare-earth elements (REEs), the world may face a serious challenge in supplying some REEs such as neodymium and dysprosium soon. Recycling secondary sources is strongly recommended to mitigate the supply risk of REEs. Hydrogen processing of magnetic scrap (HPMS) as one of the best approaches for magnet-to-magnet recycling is thoroughly reviewed in this study in terms of parameters and properties. The processes of hydrogen decrepitation (HD) and hydrogenation–disproportionation–desorption–recombination (HDDR) are two common methods for HPMS. Employing a hydrogenation process can shorten the production route of new magnets from the discarded magnets compared to other recycling routes such as the hydrometallurgical route. However, determining the optimal pressure and temperature for the process is challenging due to the sensitivity to the initial chemical composition and the interaction of temperature and pressure. Pressure, temperature, initial chemical composition, gas flow rate, particle size distribution, grain size, and oxygen content are the effective parameters for the final magnetic properties. All these influencing parameters are discussed in detail in this review. The recovery rate of magnetic properties has been the concern of most research in this field and can be achieved up to 90% by employing a low hydrogenation temperature and pressure and using additives such as REE hydrides after hydrogenation and before sintering.

Approaching enzymatic catalysis with zeolites or how to select one reaction mechanism competing with others

Abstract: Approaching the level of molecular recognition of enzymes with solid catalysts is a challenging goal, achieved in this work for the competing transalkylation and disproportionation of diethylbenzene catalyzed by acid zeolites. The key diaryl intermediates for the two competing reactions only differ in the number of ethyl substituents in the aromatic rings, and therefore finding a selective zeolite able to recognize this subtle difference requires an accurate balance of the stabilization of reaction intermediates and transition states inside the zeolite microporous voids. In this work we present a computational methodology that, by combining a fast high-throughput screeening of all zeolite structures able to stabilize the key intermediates with a more computationally demanding mechanistic study only on the most promising candidates, guides the selection of the zeolite structures to be synthesized. The methodology presented is validated experimentally and allows to go beyond the conventional criteria of zeolite shape-selectivity.