Multistep Kinetics Research Articles

Study on the reduction of Fe2O3 pellets by CO-CO2 and H2-H2O: Reaction kinetics and pore network model

The steel industry contributes to creating an environmentally friendly society by providing high-quality steel and working to develop low-carbon processes. Using hydrogen produced from renewable energy to replace part of coke in blast furnaces is one of the measures to reduce fossil carbon dioxide emissions in the process of steelmaking. In this paper, a series of reduction experiments of Fe2O3 pellets at different temperatures were carried out under three conditions of hydrogen-rich in blast furnace. The variation law between reduction degree and apparent activation energy was calculated. The result shows that when the reduction degree reaches 11% and 70%, the apparent activation energy reaches the peak, which are 38.9 kJ/mol and 19.5 kJ/mol, respectively. This suggests that the reduction process is affected by two or more mechanisms. Then, on the basis of the typical single interface reaction kinetics model, the multistep reduction kinetics model of hydrogen-rich reduction Fe2O3 pellets was established. In addition, based on the results of industrial computerized tomography (CT) analysis, the three-dimensional pore network model and velocity model of Fe2O3 pellets after reduction were established. The coupling relationship between the fractal dimension of pellet pores and reduction atmosphere was studied by introducing fractal theory. Under hydrogen-rich reduction condition, the volume fractal dimension of pore structure of Fe2O3 pellets increases from 2.41 to 2.58. Therefore, the pore structure formed by hydrogen-rich reduction is conducive to the diffusion of reducing gas in the pellet, so as to improve the reduction degree of pellet.

A combined analysis of the drying and decomposition kinetics of wood pyrolysis using non-isothermal thermogravimetric methods

In this paper, we evaluate the pyrolysis of wood biomass as a combination of drying and thermal decomposition via the Page and modified Page models for drying kinetics as well as the Friedman and Vyazovkin methods for solid-state decomposition kinetics. This approach was applied to data obtained from thermogravimetric analysis of three wood species (spruce, pine, and birch) at 5, 20, and 30 K/min temperature programs.According to the Page model, the average activation energies for spruce, pine, and birch wood between 30 and 150 °C were 12.87 ± 1.08, 13.32 ± 0.48, and 11.61 ± 0.59 kJ/mol, respectively. While all activation energies fell between 11.0 and 14.5 kJ/mol, the modified Page model predicted slightly higher energies, with an average absolute difference of 6.4% from Page's predictions. The activation energies and pre-exponential factors predicted by both models were lower at low heating rates, with the pre-exponential factor yielding significantly large differences between 5 and 30 K/min. These results showed that drying kinetics were significantly affected by heating rates. In addition, the goodness-of-fit analysis revealed that both models were reasonably accurate when predicting wood drying kinetics.For the analysis of solid-state decomposition kinetics, a comparison of Friedman's linear differential method (FR) and Vyazovkin's nonlinear integral method (NLN-INT) was conducted at temperatures higher than 150 °C. In contrast to the NLN-INT method, the FR method predicted activation energies slightly higher, with an average absolute difference of about 8.4%. Evaluation of the relative errors revealed that both the FR and NLN-INT methods performed similarly. However, the Friedman (FR) method provided a reasonable fit to multistep decomposition kinetics through the simultaneous estimation of activation energies and pre-exponential factors. Nevertheless, the activation energies estimated by both the FR and NLN-INT methods were unreliable at conversions of α < 0.15 and α > 0.85. Validation of the kinetic results was conducted with differential thermogravimetric data at a heating rate of 5 K/min.

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Coupling covariance matrix adaptation with continuum modeling for determination of kinetic parameters associated with electrochemical CO2 reduction

Some limitations of the Fraser-Suzuki function for fitting thermokinetic curves

Mathematical deconvolution (MD) can offer a simple way to solve independent multistep kinetics. However, there are always doubts about the cases in which it loses efficiency.This work analyzes the adjustability of the Fraser-Suzuki function (FSF) for processes with F0, D1, and Pn models. Curves dα/dt vs t for were simulated and fitted using the FSF for each case. Their kinetic parameters were determined and compared with the real ones. Furthermore, an example of deconvolution was analyzed. The results show that the FSF fit does not lead to satisfactory results when applied to dα/dt vs t curves that show sharp peaks and sudden decays.This work is not intended to discourage MD use since it has led to correct parameters in many investigations. However, the aim is to show examples of limitations so that the analyst can choose other appropriate approaches. Therefore, MD should always be used with caution and judgment.

Multistep kinetic study of Fe2O3 reduction by H2 based on isothermal thermogravimetric analysis data deconvolution

The multistep kinetics of Fe2O3 reduction by H2 is investigated by data deconvolution in this study. The reduction process was conducted in a TGA apparatus isothermally in the temperature range of 750–950 °C. The stepwise reduction of Fe2O3, i.e. Fe2O3–Fe3O4, Fe3O4–FeO, and FeO–Fe, was successfully decoupled from each other without controlling the reduction gas atmosphere. The overlapping, as well as the reaction rate, of each reduction step can be described by the deconvoluted data with R2 > 0.995 for all the tested temperatures. Based on the deconvolution, relatively stable activation energy with increasing the conversion was obtained for each step with the model-free iso-conversion method, indicating the rationality of the decoupled multistep profiles. Master plot was then applied to evaluate the suitability of kinetic models reported in the open literature. The JMA model (Avrami-Erofe'ev equation), corresponding to the nucleation and growth mechanism, was found to be most suitable for describing each reduction step. The activation energies obtained by the JMA model fitting for Fe2O3–Fe3O4, Fe3O4–FeO, and FeO–Fe were 10.3, 26.7, and 24.8 kJ/mol, respectively, which also agree well with the Ea obtained by the model-free method.

Comparative bio-energy potential of De-oiled coconut pulp and Coconut shell: Insights from physicochemical characterization, pyrolysis kinetics and thermodynamic studies

It is critical to study the bioenergy potential of De-oiled coconut pulp (a new biomass material) in comparison with Coconut shell which are two major wastes from Coconut fruit often disposed of by Coconut oil processing mills, in tropical countries especially Nigeria. Their comparative potential as a bioenergy source was assessed via physicochemical and thermo-chemical characteristics. Both biomass wastes were heated from ambient temperature to 1123.15 K at 5, 10, 15, 20, and 30 K∙min−1. A global dynamic mechanism from the Coats-Redfern model–fitting method was applied to non-isothermal data, using isoconversional methods, to obtain the non-isothermal kinetic and thermodynamic parameters. The physicochemical analysis of the biomass wastes revealed that De-oiled coconut pulp has the potential to produce lighter volatile products but the Coconut shell will produce relatively heavier but cleaner products from a less problematic pyrolysis process. The average apparent activation energies (Ea) from Friedman, FWO, and KAS methods for De-oiled coconut pulp were 333.1 kJ∙mol−1, 316.08 kJ∙mol−1, and 342.01 kJ∙mol−1 while for Coconut shell were 185.29 kJ∙mol−1, 178.75 kJ∙mol−1, and 176.98 kJ∙mol−1 respectively. The dynamic mechanism function, f(α), for reaction order from the Coats-Redfern model–fitting method, were (1 - α)4.2 and (1 - α)6.35 for De-oiled coconut pulp and Coconut shell respectively. Experimental values of differential change in weight with respect to temperature were in good agreement with Friedman model predictions for the pyrolysis of De-oiled coconut pulp at 5 K∙min−1 and 30 K∙min−1 (R2 = 0.7025 and 0.7495, RMSE = 0.087 and 0.1313 respectively) and for the pyrolysis of Coconut shell at 10 K∙min−1 (R2 = 0.8743, RMSE = 0.0663). F-test confirmed the fitness of the model predictions with experimental data. KAS and FWO established ΔG as a thermodynamic property of a great potential utility. The thermodynamic properties revealed that the pyrolysis of both biomass wastes was endothermic. The physicochemical properties established that both biomass wastes are potential bioenergy sources. The level of mass conversion was dependent on the apparent activation energy Ea which confirms proof of multi-step decomposition kinetics, an assumption made for isoconversional model development. Biomass reactivity in pyrolysis is critical to the application of reaction order from Coats-Redfern isothermal kinetics to non-isothermal kinetics.

Effects of Mixing and Particle Size on the Kinetics and Dynamics of Enzymatically Treated Cotton Cellulose (MCC) in Continuous Flow Reactor.

Enzymatic hydrolysis (EH) of cellulosic biomass needs tremendous technological advancement so as to efficiently convert cellulosic biomass into renewable fuels and commodity chemicals. Therefore, development of highly improved process engineering techniques is inevitable to reduce the processing cost of the fluids in the reactor. In this investigation, effect of mixing and particle size on the EH of microcrystalline cotton cellulose (MCC) has been investigated by using a spatially averaged low-dimensional two-mode mixing (TMM) model. The model simulations were carried out for the average particle sizes of MCC ranging from 0.78 to 25.52μm and mixing speed of η → 0 (very high) to η → 1000 (very low). The effects of mixing and particle size on the formation of glucose and reducing sugar (RS) have been quantified by exploiting the rigorous multistep reaction kinetics and TMM model. To access the bond-breaking ability, its effects on the degree of polymerization (DP) was also analyzed. The results deduced that increase in mixing limitations and reduction in particle size imparts a significant increase in glucose and RS yield while decreasing the DP drastically. Thus, our simulations reveal that while η → 1000 economizes the process by reducing the energy requirements, reduction in particle size can be beneficial for reducing the residence time in the depolymerization of MCC to fuels and chemicals.

Artificially Layered CoSe2 Nanosheets by a Dual-Templating Strategy for High-Performance Lithium-Sulfur Batteries.

Owing to the attractive merits of layered transition metal dichalcogenides (LTMDs) with van der Waals interactions, it is significant to modulate electronic structures and endow them with fascinating physiochemical properties by converting a nonlayered metal dichalcogenide into an atomic layered one. Herein, a dual-templating strategy is designed to prepare artificially layered CoSe2 nanosheets on carbon fiber cloth (L-CoSe2/CFC). It is found that not only the nanosheet morphology but also the layered structure is well inherited from the precursor of layered Co(OH)2 nanosheets through a wet-solution ion-exchange approach. The as-prepared L-CoSe2/CFC serves as an efficient multifunctional interlayer to solve the challenges of "shuttling effect" and slow multistep reaction kinetics in lithium-sulfur batteries (LSBs), thus dramatically improving their electrochemical performance. Benefiting from the L-CoSe2 nanosheets with large interlayer spacing, strong chemical adsorption, and superior catalytic activity, L-CoSe2/CFC promotes the anchoring of lithium polysulfides (LiPSs) and their catalytic conversion. Consequently, the L-CoSe2/CFC cell yields a large reversible capacity of 1584 mAh g-1 at 0.2C and a high rate capability of 987 mAh g-1 at 4C. A high areal capacity of 4.38 mAh cm-2 after 100 cycles at 0.2C is achieved for the high-S-loading LSB (4.6 mg cm-2) using the L-CoSe2/CFC interlayer.

Numerical study of thermal diffusion in a passive autocatalytic recombiner: Possible effects on catalyst temperature and hydrogen distribution

This paper describes a numerical study of the influence of thermal diffusion (the Soret effect) on the operational behaviour of a passive autocatalytic recombiner (PAR). The study proposes a detailed three-dimensional computational fluid dynamics (CFD) model of hydrogen oxidation along a cylindrical-type PAR catalyst section (RVK-500, RET, Russia) inside a small-scale vertical channel. The CFD model was developed in STAR-CCM+ and uses multi-step chemical kinetics with a conjugated approach (surface and gas-phase included). The catalyst temperature and hydrogen conversion with and without the Soret effect in the model were determined numerically and compared against experimental measurements. The experiments reported here have previously been conducted on the cylindrical-type catalyst section, for 5–7 vol % inlet H2 concentration. Numerical simulations demonstrate that local hydrogen concentration can be increased due to thermal diffusion at the lower side of the stainless-steel frame. Results identified that the catalyst temperature can be underpredicted by 10–20 °C without thermal diffusion included in the model.

Understanding the lithium–sulfur battery redox reactions via operando confocal Raman microscopy

The complex interplay and only partial understanding of the multi-step phase transitions and reaction kinetics of redox processes in lithium–sulfur batteries are the main stumbling blocks that hinder the advancement and broad deployment of this electrochemical energy storage system. To better understand these aspects, here we report operando confocal Raman microscopy measurements to investigate the reaction kinetics of Li–S redox processes and provide mechanistic insights into polysulfide generation/evolution and sulfur deposition. Operando visualization and quantification of the reactants and intermediates enabled the characterization of potential-dependent rates during Li–S redox and the linking of the electronic conductivity of the sulfur-based electrode and concentrations of polysulfides to the cell performance. We also report the visualization of the interfacial evolution and diffusion processes of different polysulfides that demonstrate stepwise discharge and parallel recharge mechanisms during cell operation. These results provide fundamental insights into the mechanisms and kinetics of Li–S redox reactions.

(Keynote) Deciphering Electrocatalytic Reactions with Theory and Computation: The Case of CO2 Reduction

The interfacial region between metal surface and aqueous electrolyte is of central importance for electrochemical reactions. The need to understand the properties of this electrochemical double layer (EDL) region drives extensive research.1,2 A foremost goal of research in electrocatalysis is the development of a theoretical-computational framework. The fundamental task for such a framework is to unravel the complex interplay of electronic structure effects of the catalyst material, potential-induced variations of the chemisorption state, local reaction conditions on the electrolyte side, and electrochemical kinetics of reactions of interest. A recently developed theoretical approach revealed the non-monotonic charging behaviour of a Pt electrode3 and it was thereafter used to decipher the oxygen reduction reaction.4 In the present work, we adapt this approach to study how the local reaction environment dictates the mechanism and kinetics of reduction to CO at an Ag electrode. Our hierarchical model accounts for the multistep reaction kinetics of surface reactions, local chemical equilibria (involving CO2, HCO3 -, CO3 2-, OH-, H+), the specific surface charging state at a given electrode potential, solvent polarization and ion density variations, and reactant/product transport. It integrates interface and pore-level models to account for this interplay. The combined approach rationalizes the impact of the considered effects on the kinetics of the reaction, manifested experimentally in changes of the effective Tafel slope as a function of electrode potential. Lateral interactions between chemisorbed species are seen to contribute to the decrease of the CO current density at high electrode potentials, in addition to mass transport effects, surface charging effects and pH increase. We will conclude with a discussion of the parameters that allow tuning the local reaction environment and thus the electrocatalytic activity and selectivity of the electrocatalyst. 1O.M. Magnussen and A. Gross, Toward an Atomic-Scale Understanding of Electrochemical Interface Structure and Dynamics, J. Am. Chem. Soc. 141, 4777–4790 (2019). 2M.J. Eslamibidgoli and M.H. Eikerling, Approaching the Self-consistency Challenge of Electrocatalysis with Theory and Computation, Current Opinion in Electrochemistry 9, 189-197 (2018). 3J. Huang, A. Malek, J. Zhang and M.H. Eikerling, Non-monotonic Surface Charging Behavior of Platinum: A Paradigm Change, J. Phys. Chem. C 120, 13587-13595 (2016). 4J. Huang, J. Zhang and M. Eikerling, Unifying Theoretical Framework for Deciphering the Oxygen Reduction Reaction on Platinum, Phys. Chem. Chem. Phys. 20, 11776-11786 (2018).

A novel amino acid site of N protein could affect the PRRSV-2 replication by regulating the viral RNA transcription

BackgroundFinding the key amino acid sites that could affect viral biological properties or protein functions has always been a topic of substantial interest in virology. The nucleocapsid (N) protein is one of the principal proteins of the porcine reproductive and respiratory syndrome virus (PRRSV) and plays a vital role in the virus life cycle. The N protein has only 123 or 128 amino acids, some of key amino acid sites which could affect the protein functions or impair the viral biological characteristics have been identified. In this research, our objective was to find out whether there are other novel amino acid sites of the N protein can affect N protein functions or PRRSV-2 replication.ResultsIn this study, we found mutated the serine78 and serine 99of the nucleocapsid (N) protein can reduce the N-induced expression of IL-10 mRNA; Then, by using reverse genetics system, we constructed and rescued the mutant viruses, namely, A78 and A99.The IFA result proved that the mutations did not affect the rescue of the PRRSV-2. However, the results of the multistep growth kinetics and qPCR assays indicated that, compared with the viral replication ability, the titres and gRNA levels of A78 were significantly decreased compared with the wild-type. Further study showed that a single amino acid change from serine to alanine at position 78 of the N protein could abrogates the level of viral genomic and subgenomic RNAs. It means the mutation could significant decrease the viral replication efficiency in vitro.ConclusionsOur results suggest that the serine78 of N protein is a key site which could affect the N protein function and PRRSV replication ability.

Experimental research on multistep decomposition kinetics of ammonium perchlorate in the space-confined environment

Experimental research on multistep decomposition kinetics of ammonium perchlorate in the space-confined environment

Advances and Prospects of 2D Graphene‐Based Materials/Hybrids for Lithium Metal–Sulfur Full Battery: From Intrinsic Property to Catalysis Modification

Rechargeable lithium–sulfur (Li–S) full batteries hold practical promise for next‐generation energy storage system owing to low cost and unparalleled theoretical energy density of 2600 W h kg−1. However, wide commercialization is severely hampered by the poor conductivity of S/Li2S, worrisome polysulfide shuttling effect, sluggish multistep reaction kinetics, and uncontrolled lithium dendrite growth. 2D materials show the advantages in suppressing polysulfide shuttling and boosting lithium diffusion kinetics through rational modifications of surface chemistry and nanostructure design, greatly enhancing battery performances. In this review, the recent developments of 2D graphene‐based materials in propelling the conversion/plating kinetics of Li–S full batteries are highlighted from intrinsic conductive property to adsorption and catalysis modifications. Specifically, with the functionalization of the pore morphology and heteroatom/metal atom doping in the pristine/hybrid matrix, the adsorption ability and the lithium diffusion kinetics are significantly enhanced in both cathodic and anodic side, so that the interconversion kinetics of sulfur species are propelled to inhibit polysulfide shuttling and lithium‐ion flux is homogenized to realize uniform deposition without any dendrite growth. Furthermore, challenges and opportunities for future fully development of Li–S batteries based on 2D graphene‐based materials are prospected from interfacial mechanisms at the atomic/molecular level to large‐scale production.

Slot‐Die‐Coated Organic Solar Cells Optimized through Multistep Crystallization Kinetics

To fabricate organic solar cells (OSCs) via slot‐die coating, solvent additives are essential to induce an optimized phase‐separated and order morphology. It is critical to determine the morphological evolution from solution to solid state and understand the crystallization kinetics in slot‐die coating. Using in situ grazing‐incidence wide‐angle X‐ray scattering characterization, the morphological evolution in PM6‐ and ITIC‐based systems without or with 0.3% 1,8‐diiodooctane (DIO) as additive can be monitored in real‐time during slot‐die coating. As a result, DIO weakens the planarization of the PM6 backbone and splits the backbone ordering into fragments to form ordered crystallites. DIO also induces surface crystallization to reinforce the tie‐chain connections between the crystallites. Furthermore, in the ITIC system, DIO triggers the formation of an interconnected fibril network morphology and concurrently promotes the stacking of ITIC molecules in between the polymer network. Thus, an optimized morphology with a refined crystal structure is formed with the help of DIO. As a result, the power conversion efficiency is improved from 8.77% to 9.59% in slot‐die‐coated OSCs. These findings provide guidelines for optimizing the morphology in slot‐die‐coated OSCs and accelerate the transition of laboratory‐scale fabrication to industrial production.

Chemically Fueled Self-Sorted Hydrogels.

Narcissistic self-sorting in supramolecular assemblies can help to construct materials with more complex hierarchies. Whereas controlled changes in pH or temperature have been used to this extent for two-component self-sorted gels, here we show that a chemically fueled approach can provide three-component materials with high precision. The latter materials have interesting mechanical properties, such as enhanced or suppressed stiffness, and intricate multistep gelation kinetics. In addition, we show that we can achieve supramolecular templating, where pre-existing supramolecular fibers first act as templates for growth of a second gelator, after which they can selectively be removed.

Assessing the thermal and fungal behavior of eco-friendly epoxy thermosets derived from vegetable oils for wood protective coatings

The paper deals with the study of the obtaining, characterization and thermal and fungal behavior of a green thermoset based on epoxidized soybean oil (ESO), castor oil maleic anhydride adduct (COMA) and methyl nadic anhydride (MNA). By varying the MNA/COMA crosslinking agent ratio, resins with different degree of stiffness can be obtained suitable for green thermosets coatings. Differential scanning calorimetry (DSC) and a simultaneous TG/FT-IR/MS coupling were used to establish the crosslinking behavior, evolved gases analysis and thermal decomposition mechanisms associated with their corresponding kinetic parameters. The non–isothermal global kinetic parameters values (activation energy and pre–exponential factor) were calculated with the aid of the Friedman and Flynn–Wall–Ozawa isoconversional methods. The curves shape of the variation of activation energy versus conversion degree and first derivative (DTG) curves shapes suggest that the thermal degradation processes occurred in multi-step kinetics. Using a multivariate linear regression method the most probable thermal decomposition and crosslinking kinetic models were established. A good concordance between experimental and simulated data was obtained, confirming the correct description of the thermal mechanisms. The main identified gaseous fragments were water, carbon dioxide, saturated and unsaturated hydrocarbons and carboxylic derivatives. The decay resistance against two wood decaying strains, P. chrysogenum and A. brasiliensis was also evaluated.

Electrochemical CO2 Reduction at Silver from a Local Perspective

The electrochemical reduction of CO2 to chemical fuels and value-added chemicals is a viable pathway to store renewably generated electrical energy and to mitigate the negative impact of anthropogenic CO2 production. Herein, we study how the local reaction environment dictates the mechanism and kinetics of CO2 reduction to CO at an Ag electrode. The local reaction environment is determined using a hierarchical model that accounts for multistep reaction kinetics, specific surface charging state at a given electrode potential, and mass transport phenomena. The model reveals vital mechanistic insights into the reaction behavior. The increasing Tafel slope with overpotential is seen to be influenced by the surface charging relation and mass transport effects. In addition, the decrease of the CO current density at high overpotentials is found to be caused not only by the decrease in CO2 concentration due to mass transport, surface charge effects, and pH increase but also by lateral interactions between HCOOad, COOHad, and Had. Moreover, we explore how the electrolyte properties, including bicarbonate concentration, solvated cation size, and CO2 partial pressure, tune the local reaction environment.

Combustion characteristics of a porous media burner with partial hydrogen injection

Multiple energy sources are combined to solve the shortage due to more and more energy consumption. Hydrogen as an ideal clean and renewable energy was injected to the porous media burner to realize the utilization with methane simultaneously. The numerical model of double-layer structure imported with multi-step kinetics mechanisms was built to study the effects of hydrogen injecting position and width on the combustion characteristics of methane after the experimental validation. Results indicate that the axial temperatures during the hydrogen injection at the upstream and interface positions were obviously higher than that at the downstream position. With the increasing of hydrogen injection width, the overall temperature gradually decreased, which was corresponding to the decreasing trend of CO and NOx emissions. However, the temperature and pollutant emissions increased as the equivalence ratio of methane and hydrogen increased. In addition, the increasing of methane and hydrogen velocity increased the CO emission and decreased the NOx emission.

Modelling electrocatalytic reactions with a concerted treatment of multistep electron transfer kinetics and local reaction conditions

A physicochemical model is developed for electrocatalytic reactions involving multiple electron transfer steps occurring in the electric double layer (EDL). The local reaction conditions are calculated using a mean-field EDL model, which is derived from a comprehensive grand potential that considers the steric effects, solvent polarization, and chemisorption-induced surface dipoles. Macroscopic mass transport in the so-called diffusion layer is controlled by the same set of controlling equations of the EDL model, without imposing the electroneutrality assumption as usual. The Gerischer’s formulation of electron transfer theory, corrected with local reaction conditions, is used to describe the kinetics of elementary steps. Multistep kinetics of the electrocatalytic reaction is treated using microkinetics modelling, without resorting to the usual rate-determining step approximation. In formal analysis of the model, we retrieve canonical models with additional assumptions. Self-consistent numerical implementation of the model is demonstrated for oxygen reduction reaction (ORR) at Pt(111) in acidic solution, and the aptness of the model is verified by comparison with experimental data. A comparative study of the full model and its simplified versions allows us to examine how the ORR is influenced by asymmetric steric effects, finite concentration of ions, solvent polarization, surface charge effects, and metal electronic structure effects. We find that the difference in terms of the overpotential between the full model and the simplest model can be up to ∼0.1 V at a current density of −6 mA .