Reaction Chemistry Of Complexes Research Articles

Advances in Cathodes for High-Performance Magnesium-Sulfur Batteries: A Critical Review

Large-scale energy storage with high performance and at a reasonable cost are prerequisites for promoting clean energy utilization. With a high theoretical energy density of 1722 Wh·kg−2, high element abundance (e.g., Mg of 23,000 ppm, S of 950 ppm on earth), and low theoretical cost, Mg-S batteries offer considerable potential as candidates for electrical energy storage. However, due to the intrinsic complex reaction chemistry of sulfur cathodes and metal anodes, such as slow diffusion of the divalent ion, the shuttle of soluble polysulfide, and irreversible deposition of Mg ions on metal electrodes, Mg-S batteries still need further optimization to meet requirements for practical applications. In addition to stabilizing metal anodes, developing a suitable sulfur cathode is desperately needed. This review summarizes recent research progress in sulfur cathodes, interlayers, and non-nucleophilic electrolytes, highlighting the main challenges and corresponding strategies for electrode material designs. Notably, we emphasize a fundamental understanding of the structure-composition relationship. Furthermore, state-of-the-art characterization techniques are described that help reveal the pertinent electrochemical mechanisms whereby Mg-S cells function. Finally, possible research directions are discussed.

Dynamics of Rubisco regulation by sugar phosphate derivatives and their phosphatases.

Regulating the central CO2-fixing enzyme Rubisco is as complex as its ancient reaction mechanism and involves interaction with a series of cofactors and auxiliary proteins that activate catalytic sites and maintain activity. A key component among the regulatory mechanisms is the binding of sugar phosphate derivatives that inhibit activity. Removal of inhibitors via the action of Rubisco activase is required to restore catalytic competency. In addition, specific phosphatases dephosphorylate newly released inhibitors, rendering them incapable of binding to Rubisco catalytic sites. The best studied inhibitor is 2-carboxy-d-arabinitol 1-phosphate (CA1P), a naturally occurring nocturnal inhibitor that accumulates in most species during darkness and low light, progressively binding to Rubisco. As light increases, Rubisco activase removes CA1P from Rubisco, and the specific phosphatase CA1Pase dephosphorylates CA1P to CA, which cannot bind Rubisco. Misfire products of Rubisco's complex reaction chemistry can also act as inhibitors. One example is xylulose-1,5-bisphosphate (XuBP), which is dephosphorylated by XuBPase. Here we revisit key findings related to sugar phosphate derivatives and their specific phosphatases, highlighting outstanding questions and how further consideration of these inhibitors and their role is important for better understanding the regulation of carbon assimilation.

Exploration of the Unique Structural Chemistry of Sulfur Cathode for High‐Energy Rechargeable Beyond‐Li Batteries

The increased demand for energy has prompted users to seek alternative energy storage devices. Post‐Li‐ion battery chemistries have been considered potential contenders for the development of next‐generation battery technologies. The high specific capacity (≈1675 mAh g−1) and high natural abundance (≈953 ppm) of sulfur provide opportunities to meet the rigorous requirements of the market's demands, such as high energy density and low cost. When combined with a high capacity metal anode (e.g., Na ≈ 1165 mAh g−1, Mg ≈ 2205 mAh g−1, and Al ≈2980 mAh g−1), it leads to high energy density that can outperform the existing battery technologies, including high‐energy Li‐ion batteries. Despite the unique attributes of the sulfur‐based battery system, it remains in infancy owing to the complex reaction chemistry of sulfur cathode, and the level of complexity increases with an increase in valency of metal ions. This review summarizes the unique aspects of a sulfur cathode essential to stabilizing sulfur cathode‐based high‐energy rechargeable batteries. Furthermore, deeper insight into the electrochemical performance of various metal–sulfur‐based systems has been provided. This review may pave the path for the researchers to accelerate the development of sulfur cathode for post‐Li‐ion batteries.

Thermodynamics, kinetics and thermal decomposition characteristics of sewage sludge during slow pyrolysis

Pyrolysis has shown great potential for sewage sludge valorisation and management by producing value-added chemicals. Although the product process yields are extensively studied, a few studies exist without consensus on the kinetic properties of sewage sludge pyrolysis. As a result, a study to investigate the thermal decomposition characteristics of Gauteng sewage sludge (GSS) at various heating rates (10, 20, and 30 °C/min), its pyrolysis kinetic parameters, reaction mechanism and thermodynamic properties was meticulously conducted. The results show that sewage sludge decomposition occurs in three stages, whereby the main decomposition (active pyrolysis) takes place at 150–570 °C. Fourier transform infrared spectroscopy (FTIR) analysis results confirm progression of thermal decomposition of GSS and drive off volatile compounds and formation of aromatic structures during TGA studies of GSS. An increase in heating rate shifts the characteristic temperatures towards higher temperatures with the highest decomposition rate of 1.10%/min.mg at 30 °C/min. The activation energies of GSS pyrolysis were calculated using Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose and Starink methods and averaged as 225.92, 218.04 and 218.97 kJ/mol, respectively. GSS pyrolysis involves complex reaction chemistry with high reactivity whereby reactions that follow third order and three-dimensional diffusion-reaction mechanisms dominated the process. However, these mechanisms cannot be used explicitly to define the global pyrolysis kinetics due to the occurrence of multiple simultaneous reactions. The obtained thermodynamic and kinetic data will advance and amplify the design, simulation and optimisation of global energy pyrolysis units for production of value-added chemicals.

Prediction of Hydrothermal Carbonization with Respect to the Biomass Components and Severity Factor

In recent years, hydrothermal carbonization (HTC) has been introduced as an attractive method for converting biomass into value-added products. The complex reaction chemistry and variable compositi...

Getting the chemicals right: Toward characterizing toxicity and ecotoxicity impacts of inorganic substances

Characterizing human and ecological exposure and toxicity impacts from emissions of chemical substances along life cycles of consumer products and industrial processes is an important building block in several decision support frameworks. Various products and processes involve the use of inorganic substances, such as inorganic salts, acids, and bases. However, except selected metal ions, inorganic substances are currently not included in any existing chemical toxicity characterization framework, leaving an important gap unaddressed in current assessments of environmental performance of products and services, chemical substitution, and substance prioritization. To address this gap, we provide initial guidance for identifying and characterizing toxicity-related impacts of currently unconsidered inorganic substances. Starting from a chemical classification of inorganic substances, we determine both the economic and environmental relevance of inorganic compounds currently registered under the European REACH regulation, and combine both to identify substances that should be prioritized for future toxicity characterization. Further, we provide an overview of current challenges and outline possible ways forward toward incorporating inorganic substances into toxicity characterization models. We identified approximately 90 inorganic priority substances that are both of high economic as well as of high environmental relevance. Current characterization methods need to be adapted and extended to account for the complex reaction chemistry and data limitations for effect quantification of inorganic substances. Future research is required that targets the inorganic reaction chemistries and that overcomes current data limitations. This will ultimately lead to a more comprehensive decision support in line with the global sustainability agenda set for chemicals management.

Assembly and stabilization of {E(cyclo-P3)2} (E = Sn, Pb) as a bridging ligand spanning two triaryloxyniobium units.

Complexes (THF)0-2E[P3Nb(ODipp)3]2 (E = Sn, Pb; Dipp = 2,6-(i)Pr2C6H3) were isolated (>90%) from the salt metathesis of [Na(THF)3][P3Nb(ODipp)3] with E(2+) salts. The reaction of (THF)Sn[P3Nb(ODipp)3]2 with pyridine-N-oxide was investigated as a method to deposit a new SnP6 phase. Additionally, the neutral complex P3Nb(ODipp)2(py)2 (py = pyridine) was prepared from [Na(THF)3][P3Nb(ODipp)3] in the presence of pyridine and salts of coordinating cations (Mg(II), Sn(II), Pb(II), Ge(II), Hg(II) and Ag(I)). P3Nb(ODipp)2(py)2 was found to successfully produce AsP3 upon treatment with AsCl3. The characterization of complexes (THF)0-1Sn[P3Nb(ODipp)3]2, (THF)2Pb[P3Nb(ODipp)3]2 and P3Nb(ODipp)2(py)2, including their solid state structures, is discussed.

Dynamic modeling and optimization of an industrial fluid catalytic cracker

Fluid Catalytic Cracking (FCC) is an important process which is used to convert heavy petroleum fractions into more valuable lighter products. In this work, the FCC process consists of the reactor, the regenerator and the fractionation units. Modeling is challenging due to the complex reaction chemistry and the interactions among the different process units. The reaction medium is modeled by the method of discrete lumping that uses narrow fractions. As a result, the number of discrete lumps (or pseudo-components) to model the process increases and this enables better prediction of fractionation products. For the reactor, we present a new kinetic model that includes a yield function for the cracking products. Kinetic constants and heat of cracking are correlated with the average boiling point of the pseudo-components. These correlations are next used in the development of first-principles models for the riser and the regenerator units. In addition, an empirical model is constructed for the purpose of predicting the individual amounts of the fractionation products from the reactor's effluent. Using parameter estimation, model parameters are estimated from actual industrial data. Model predictions match the plant measurements closely. Simulation and optimization results show that the developed model offers significant potential for use in real-time optimization and control.

Hydrothermal Carbonization of Biomass for Energy and Crop Production

AbstractHydrothermal carbonization (HTC) is a thermochemical pretreatment process where biomass is treated under hot compressed water to produce hydrochar. Hydrochar is a stable, hydrophobic, friable solid product, which has a fuel value similar to that of lignite coal. Among its other advantages, its capability to handle wet feed makes the HTC process most attractive. The complex reaction chemistry of HTC offers a huge potential for producing a variety of products, from fuel to supercapacitors, from carbon nanospheres to low cost adsorbents, from fertilizers to soil amenders. Hydrochar opens possibilities for replacing coal in existing coal-power plants. Its high surface area and adsorption characteristics make it compatible for use in supercapacitors. Hydrochar also contains high amounts of stable carbon and other nutrients, which are essential for soil amendment. Moreover, the HTC process liquid, especially if a short retention time is used, contains potentially toxic substances like phenols, furfurals, and their derivatives, which open opportunities for anaerobic digestion to produce biogas. This review paper gives an overview of the HTC process parameters, reactions, and the use of hydrochar for energy and crop production

Revisiting the steady states of NO/O2/C3H6 on monolithic Pt/BaO/Al2O3 using bifurcation analysis

While NOx storage and reduction is periodically operated, steady‐state studies have been widely carried out to investigate the involved reaction mechanisms and effects of operating parameters. Due to the complex reaction chemistry and its coupling with transport phenomena, multiplicity may exist. A steady‐state monolith reactor model accounting for microkinetics and reaction heat effects was proposed in this study to avoid the evaluation of enthalpies of microreaction steps. Three simplified versions of the monolith model were developed based on various assumptions of the axial gradients. Steady‐state behaviors of NO/O2/C3H6 system were investigated. A predictor‐corrector (PC) continuation method that does not require explicit evaluation of Jacobian Matrix was developed to solve the nonlinear system with a variable parameter of feed temperature. Model predictions were compared with experimental results. © 2013 American Institute of Chemical Engineers AIChE J 60: 623–634, 2014

Reaction Chemistry of Solid-State Pyridine Thin Films with Vapor Deposited Ag, Mg, and Al

The reaction of pyridine in thin solid-state films with post-deposited Ag, Mg, and Al is investigated using surface Raman spectroscopy in ultrahigh vacuum. Vapor-deposited Ag forms metallic nanoparticles on the pyridine film, resulting in surface enhancement of the Raman scattering (SERS), with no reaction chemistry evident. Mg and Al react with pyridine by electron transfer to form radical anion intermediates, some of which are stabilized by entrapment in the solid pyridine matrix. With Mg, slight SERS enhancement is observed along with Mg-to-pyridine electron transfer to form pyridyl radical anions, some of which dimerize to 4,4′-bipyridine with loss of MgH2 and a neutral Mg atom. With Al, the reaction chemistry is initiated by a similar Al-to-pyridine electron transfer, but the radical anions so formed undergo further degradation to amorphous carbon. In total, these results demonstrate the complex reaction chemistry that can occur between heterocycles in the solid state and low work function metal atoms.

Spectroscopic Characterization of Solid Discharge Products in Li–Air Cells with Aprotic Carbonate Electrolytes

Raman, infrared, and X-ray photoelectron spectroscopies were used to characterize the thick coating of reaction products on carbon and MnO2-coated carbon cathodes produced during discharge of Li–air cells. The results show that neither Li2O2 nor Li2O are major components of the insoluble discharge products; instead, the products are composed primarily of fluorine, lithium, and carbon, with surprisingly little oxygen. The complex reaction chemistry also appears to involve the formation of ethers or alkoxide products at the expense of the carbonate solvent molecules (ethylene carbonate and dimethyl carbonate). The irreversible discharge reaction is likely electrochemically promoted with Li+, anions, and dissolved oxygen. Exactly how the molecular O2 participates in the reaction is unclear and requires further study. The addition of a conformal coating of MnO2 on the carbon lowers the cell’s operating voltage but does not alter the overall discharge chemistry.

Kinetic Modeling of Supercritical Water Reformation of JP-8 Fuel

A global first-order kinetic study is conducted for a novel supercritical water reformation process of JP-8 fuel. The process uniquely employs supercritical water both as a homogenizing reaction medium and also as a highly energetic reactant of reformation. The complex reaction chemistry is mathematically modeled using two simplified reaction mechanisms involving two different reaction sequences and routes between pyrolysis and reformation reaction steps. First-order kinetics are assumed for all mechanistic reaction rates. The mathematical models are analyzed using the kinetic data obtained on a Generation-I reactor made of Inconel 625 Grade I alloy. The crossover temperature is defined and computed as the temperature above, which the mechanistic rate of reformation of JP-8 overtakes that of the pyrolysis of JP-8 hydrocarbons. The Arrhenius kinetic parameters for both pyrolysis and reformation reactions are found based on the two mechanistic routes proposed. It is found that the two mechanistic models adequately analyze the reaction kinetics and predict the crossover temperature in a close vicinity of each other. The study not only helps elucidate the complex reaction phenomena of the novel process, but also points to the right direction of the process optimization and design of a Generation-II reactor.

Ultra-rich combustion in parallel channels to produce hydrogen-rich syngas from propane

Although hydrogen is abundant in nature, it is primarily bound into other molecules such as hydrocarbons. The conversion, or reforming, of a hydrocarbon into a hydrogen-rich syngas may be accomplished through either catalytic or non-catalytic processes. In this paper, we examine a non-catalytic reactor for syngas production that consists of multiple parallel channels with alternating flow directions. Heat recirculation between channels with opposing flow directions promotes reactions of rich mixtures beyond the conventional flammability limit. Experimental results with propane/air mixtures show that stable reaction fronts are obtained at a wide range of equivalence ratios and inlet velocities. The performance of the reactor with propane/air is compared to previously published results with methane/air mixtures, where significant differences are attributed to the more complex reaction chemistry of rich propane combustion.

Reaction Chemistry of Complexes Containing PtH, PtSH, or PtS Fragments: From Their Apparent Simplicity to the Maze of Reactions Underlying Their Interconversion

The relevance of platinum in the reaction of thiophene and derivatives with homogeneous transition-metal complexes as models for hydrodesulfurization has led us to the study of the reaction chemistry of complexes containing Pt--H, Pt--SH, and Pt--S fragments. Exploration of the reactions triggered by addition of controlled amounts of Na2S or NaSH to [Pt2(H)2(mu-H)(dppp)2]ClO4 (1) has provided evidence of the formation of complexes [Pt2(mu-H)(mu-S)(dppp)2]ClO4 (2), [Pt(H)(SH)(dppp)] (3), [Pt2(mu-S)2(dppp)2] (4), [Pt2(mu-S)(dppp)2] (5) and [Pt(SH)2(dppp)], in which dppp denotes 1,3-bis(diphenylphosphanyl)propane. Consequently, complexes 1, 2, and 5 as well as the already reported 3, 4, and [Pt(SH)2(dppp)] have been obtained and fully characterized spectroscopically. Also the crystal structures of 1 and 2 have been solved. Complexes 1-5 constitute the main framework of the network of reactions that account for the evolution of 1 under various experimental conditions as shown in Scheme 1. Apparently, this network has complexes 2 and 4 as dead-ends. However, their reciprocal interconversion by means of the replacement of one bridging hydride or sulfide ligand in the respective {Pt(mu-H)(mu-S)Pt} and {Pt(mu-S)2Pt} cores enables the closure of the reaction cycle involving complexes 1-5. Theoretical calculations support the existence of the undetected intermediates proposed for conversion from 1 to 2 and from 3 to 2 and also account for the fluxional behavior of 1 in solution. The intermediates proposed are consistent with the experimental results obtained in comparable reactions carried out with labeled reagents, which have provided evidence that complex 1 is the source of the hydride ligands in complexes 2 and 3. Overall, our results show the strong dependence on the experimental conditions for the formation of complexes 1-5 as well as for their further conversion in solution.

Copper sulphide precipitation in a fluidised bed reactor

The feasibility of the removal of a single metal (copper) by sulphide precipitation from a synthetic stream was investigated in a seeded fluidised bed reactor. The use of sulphide was motivated by high sulphate levels in local acid mine drainage and the potential integration of the metal removal process with a biological sulphate reducing process that produces an aqueous sulphide stream. Results showed that high local supersaturation and complex reaction chemistry were responsible for inefficiencies in the system, resulting in the precipitation of very fine particles and the formation of stable, soluble copper polysulphide complexes. The influence of the sulphide to copper molar ratio, recycle flow rate, inlet copper flow rate and the inlet copper concentration on the copper conversion and removal efficiency were investigated using response surface methodology to map the response surface and optimise the laboratory system. The sulphide to copper molar ratio was the most influential factor. However, the derived models were unable to account for a significant portion of the observed variation, so an optimal reactor configuration could not be determined with a high degree of confidence.

Dynamic Modeling Analysis for Control of Chemical Vapor Deposition

A nonlinear dynamic model of the chemical vapor deposition (CVD) process has been developed to aid design of a closed-loop control system. A lumped control volume analysis is used to capture important mass and fluid transients and spatial affects, while a simplified single variable equation is used to represent the complex reaction chemistry. Steady-state experimental results and model predictions are compared and the control implications of the process dynamics are discussed.

Direct production of butyltin chlorides from a paired electro-organic synthesis

Butyltin chlorides were produced directly from butyl chloride and a tin cathode in several undivided cell reactors with tetraethylammonium chloride and acetonitrile solvent. The complex reaction chemistry was investigated primarily in a small batch cell with a 1 cm2 planar cathode. Current densities from cathodic linear potential sweeps at 1 mV s−1 were correlated successfully with current densities and butyltin products from potentiostatic experiments. Potential windows on product formation and other major limiting reactions were thereby identified. Product yield was shown to be strongly dependent on electrolyte gas conditions, with yield decreasing as the reactor is increasingly deaerated. Use of the initial open circuit potential (i.o.c.p.) as an indicator of reaction gas conditions proved to be a convenient and reproducible technique. Under favourably oxidized conditions, current densities in the product formation potential region ranged from 66 mA cm−2 at −2.74V vs SCE to 250 mA cm−2 at −2.98 Vvs SCE which are considerably higher than previously reported current densities for this synthesis. Surprisingly, the aeration history of butyl chloride prior to synthesis may be an important factor in subsequent product yield.