Search

Nickel oxide was supported on MCM-41 using the precipitation method. Reduction kinetics of supported and unsupported nickel oxide was studied using non-isothermal methods to investigate the change in activation energy and the reduction reaction mechanism. Activation energy was determined using the Kissinger's method and Straink's method. Model discrimination was done using the Hancock-Sharp analysis and Malek's method. The support influenced the reduction kinetics by increasing the activation energy. The reaction mechanism shifted from Avrami-Erofeev model in the unsupported to three-dimensional diffusion-controlled model in the supported nickel oxide. The higher activation energy and the model discrimination in the case of nickel oxide supported on MCM-41 indicates the diffusion of vacancies is the rate limiting step. The reduction mechanism of nickel oxide supported on MCM-41 was proposed in agreement with literature and current study. [ABSTRACT FROM AUTHOR]

Ascorbic acid (AA) is the most widely used reductant for noble metal nanoparticle (NP) synthesis. Despite the synthetic relevance, its aqueous chemistry remains misunderstood, due in part to various assumptions about its reduction pathway which are insufficiently supported by experimental evidence. This study aims to provide an understanding of the complex chemistry associated with AA under aqueous conditions. We demonstrate that (i) AA undergoes appreciable degradation in alkaline solution on a timescale relevant to NP synthesis, (ii) contrary to popular belief, AA does not degrade into dehydroascorbic acid (DHA), nor is DHA the oxidized product of AA under noble metal NP synthetic conditions, (iii) DHA, which readily degrades under alkaline conditions, can also effectively reduce metal salt precursors to metal NPs, (iv) neither ascorbate nor dehydroascorbate act as surface capping agents post‐synthetically on the NPs (v) AA degradation time greatly affects the morphology and polydispersity of the resultant NP. Results from our mechanistic investigation enabled us to utilize purposefully‐aged reductants to achieve control over shape yield and monodispersity in the seed‐mediated synthesis of Au nanorods. Our findings have important implications for achieving monodispersed products in the many metal NP synthesis reactions that make use of AA as a reducing agent. [ABSTRACT FROM AUTHOR]

The oxide scale on the surface of hot‐rolled low‐carbon steel strips is subjected to isothermal reduction in 10 vol%H2–Ar and 20 vol%H2–Ar environments to simulate the reduction process that occurs in a continuous annealing furnace. The influence of hydrogen concentration on the reduction kinetics and the microstructural evolution of the oxide scale after reduction at temperatures ranging from 450 to 850 °C for a duration of 20 min are investigated in detail. The mass changes of the oxide scale in the two gases are quantified using a thermogravimetric analyzer. This data is then employed to calculate the reduction rate constant and the apparent activation energy. To examine the microstructure and element distribution, electron probe microanalysis and energy‐dispersive spectrometry are employed. An novel approach is also undertaken to assess the reduction degree of the oxide scale by measuring surface microhardness. In the findings, it is indicated that an increase in hydrogen concentration served primarily to accelerate the reduction reaction within the temperature ranges of 450–550 and 800–850 °C. Meanwhile, the mechanism of physical transformation of oxide scale, the microstructure of reduction layer, and hydrogen concentration on reduction efficiency under different reaction stages are proposed. [ABSTRACT FROM AUTHOR]

Organic pollutants negatively impact the environment, including air, water, soil, and living organisms. These pollutants come from various sources, including industrial, agricultural, and domestic activities. Removing organic pollutants from the environment is a difficult task and requires a combination of prevention and innovative strategies. Herein a novel nanocomposite consisting of beta‐cyclodextrin (β‐CD) modified silver (Ag@β‐CD) and gold (Au@‐β‐CD) nanoparticles (NPs) attached on the surface of Fe3O4@TiO2 core–shell structure with an average 530 nm diameter in an eco‐friendly environment is presented. In the first step, Au@‐β‐CD and Ag@‐β‐CD are synthesized, and the core–shell structure is modified by these nanoparticles. The catalytic activities of the synthesized nanocomposite are investigated for the reduction of RhB and 4‐NP and the photodegradation of MB. The synthesized composite shows the highest catalytic performance in the reduction of RhB and 4‐NP and photodegradation of MB, and the reactions are completed in 75, 45 s, and 16 min with a rate constant (k) 0.03 ± 0.005 s−1, 0.07 ± 0.01 s−1, and 0.25 ± 0.07 min−1, respectively. The reduction and photodegradation reactions follow the first‐order rate law. The catalyst is reused for six cycles after separation from the reaction system by an external magnetic field. [ABSTRACT FROM AUTHOR]

The reduction of hematite with ammonia is a potentially environmentally friendly method of ironmaking. Previous studies on ammonia reduction of pellets typically involved samples weighing only 2.8 g and lacked detailed activation energy analysis for the ammonia-hydrogen co-reduction of pellets. Therefore, to further investigate the reduction thermodynamics and kinetics of NH3–H2 reduction of pellets, this study uses 50 g pellets for reduction experiments. By increasing the pellet mass, the study expands the scope of kinetic research on ammonia reduction of pellets. The results indicate that nitrogen gas produced from ammonia decomposition reduces the equilibrium components of the reducing gas. In the temperature range of 700–850 °C, the formation of iron nitride exhibits a narrow range during ammonia reduction of hematite. In the reduction of 50 g of pellets, the reduction rate using 100% NH3 is lower than that using a 50% NH3 and 50% H2 mixed gas, which is, in turn, slower than using 100% H2. As temperature increases, the reduction effect of 50% NH3 and 50% H2 approaches that of 100% H2. Among common gas-solid reaction mathematical models, the Phase-boundary-controlled model with the Contracting Cylinder Model is selected as the most plausible mechanistic function. For the reduction of 50 g of pellets, the activation energies for reactions using 100% NH3, 50% NH3 and 50% H2, and 100% H2 are 65.42, 54.37, and 29.17 kJ/mol, respectively. The decomposition of NH3 has a negative effect on the reduction of Fe2O3. XRD analysis and electron microscopy element line scanning show that Fe4N is formed during the reduction of Fe2O3 with 100% NH3. The use of a 50% NH3 and 50% H2 mixture significantly reduces the formation of Fe4N during the reduction of the pellets. [ABSTRACT FROM AUTHOR]

Hydrogen-based smelting reduction has received widespread attention as an important technology for realizing low-carbon development in hydrogen metallurgy. In this study, the thermodynamics of smelting reduction was firstly analyzed by using FactSage 8.1 thermodynamic software, on the basis of which smelting reduction experiments of iron oxides by using bottom-blown hydrogen were carried out. The experiments used oxidized pellets as experimental materials, and the effects of the reduction process were analyzed in terms of the reduction temperature, the reduction time, and the hydrogen flow rate. The experimental results show that under the experimental conditions of a temperature of 1550 °C and a hydrogen flow rate of 0.2 Nm3/h, the reduction rate of iron oxides in the process of reducing iron oxides by hydrogen is significantly faster in the first 10 min than after 10 min. The hydrogen utilization rate reached a maximum of 41.87%, then decreased continuously and finally maintained at about 20%. Using the method of model fitting, it was found that the hydrogen-based molten reduction conformed to the phase boundary reaction model ( G α = 1 − (1 − α) 1 / 2 ), the corresponding mechanism function is f α = 2 (1 − α) 1 / 2 , where α stands for the reduction conversion, and the reaction rate constant k (T) is 2.37 × 10−4 s−1 under the experimental conditions. [ABSTRACT FROM AUTHOR]

Nickel oxide reduction kinetics and formation of the electric potential of anode-supported solid oxide fuel cell (SOFC) were studied using in situ Raman spectroscopy (RS) and conventional electrochemical techniques. It was shown that the time dependence of the electric potential and the intensity of the Raman spectra during anode substrate reduction can be conditionally divided into two stages. At the initial stage, in the first seconds after hydrogen supply, the open circuit voltage (OCV) quickly rises and stabilizes at a value of about 0.85 V. This stage is not accompanied by noticeable changes in RS. Then, there is a more gradual rise, requiring tens of minutes, to the OCV equilibrium value. The beginning of the second stage of the increase in the OCV coincides with a sharp change in the intensity of the specific spectral line in the Raman spectrum. An increase of the OCV in the first seconds after hydrogen supply is explained by an increase in the hydrogen concentration at the outer boundary of the SOFC anode. The sharp change in the intensity of the Raman spectrum, in turn, can be explained by the reduction of NiO to the metallic state in the near electrolyte region. In this work, a detailed reduction model of the NiO-YSZ (yttria-stabilized zirconia) cermet composite supporting substrate of an anode-supported SOFC was constructed. The model was developed on the assumption that the rate of the nickel oxide reduction reaction at each point of the sample depends only on the partial pressure of hydrogen, the fraction of oxidized nickel, and temperature. In the case of repeated reduction and at high temperatures, it can be assumed that the reaction has first-order kinetics, i.e., reaction rate is proportional to the fraction of oxidized nickel. At primary reduction and temperatures of 400–600 °C, the reaction is described by Avrami-Erofeev kinetics. [ABSTRACT FROM AUTHOR]

For the performance optimization strategies of hard carbon, heteroatom doping is an effective way to enhance the intrinsic transfer properties of sodium ions and electrons for accelerating the reaction kinetics. However, the previous work focuses mainly on the intrinsic physicochemical property changes of the material, but little attention has been paid to the resulting interfacial regulation of the electrode surface, namely the formation of solid electrolyte interphase (SEI) film. In this work, element F, which has the highest electronegativity, was chosen as the doping source to, more effectively, tune the electronic structure of the hard carbon. The effect of F‐doping on the physicochemical properties of hard carbon was not only systematically analyzed but also investigated with spectroscopy, optics, and in situ characterization techniques to further verify that appropriate F‐doping plays a positive role in constructing a homogenous and inorganic‐rich SEI film. The experimentally demonstrated link between the electronic structure of the electrode and the SEI film properties can reframe the doping optimization strategy as well as provide a new idea for the design of electrode materials with low reduction kinetics to the electrolyte. As a result, the optimized sample with the appropriate F‐doping content exhibits the best electrochemical performance with high capacity (434.53 mA h g−1 at 20 mA g−1) and excellent rate capability (141 mA h g−1 at 400 mA g−1). [ABSTRACT FROM AUTHOR]

Magnetization reduction roasting is an important method for the utilization of oolitic magnetite. In this study, the magnetization reduction behavior and kinetics of oolitic hematite in gas-based roasting were systematically investigated by X-ray photoelectron spectroscopy (XPS). The results revealed that under optimal roasting conditions of 650 °C, a roasting time of 60 min, and a CO concentration of 30%, the magnetization reduction rate of the roasted product reached 44.34%. Furthermore, the weak magnetic separation concentrate presented a TFe of 58.09% and a concentrate iron recovery of 94.3%. The results of the XPS spectrum indicated that the peak area ratio (Fe2+/Fe3+) gradually increased with an increase in roasting temperature, roasting time, and CO concentration, while over-reduction occurred when the roasting temperature exceeded 750 °C. The investigation of magnetization roasting kinetics for varying particle sizes demonstrated that the magnetization reduction process is controlled by chemical reaction, with a corresponding activation energy range of 42.96 kJ/mol to 63.29 kJ/mol, indicating the particle size has little effect on the magnetization reduction of oolitic hematite. [ABSTRACT FROM AUTHOR]

The article presents the results of obtaining a composite material by sintering nickel-containing raw materials mixed with carbon-containing materials, namely using coke and semi-coke. The sintering process was performed at a charge layer height of 240 mm and the temperature of the lower layer was T = 1200 °C. The results of the sieve analysis showed (a fraction of 10 mm) that the yield of a suitable composite material using coke was 68.3% and with semi-coke 67.0%. The average nickel and chromium content in the composite materials was 1.42% and 3.07%, accordingly. As a result of determining the strength characteristics of the obtained composite materials with various reducing agents by dropping from a height of 2 m onto a steel pallet, it was found that the obtained composite materials have high mechanical properties in terms of strength of 81% and 89.2%. The results of the elemental composition at the studied points and the thermal analysis of the studied composite material are presented. The mineralogical composition of the composite material is presented in the form of serpentine and nontronite, and the empty rock is made of quartz and talc. The activation energy of thermal analysis by the method of non-isothermal kinetics were calculated. The results of experiments on the production of composite materials from nickel-containing raw materials will be recommended for obtaining the optimal composition of composite materials at the stage of pilot tests and industrial development of the developed technology for processing nickel ores of the Republic of Kazakhstan. For the processing of nickel-poor nickel ores, it is of great importance to obtain optimal technological and technical and economic indicators that ensure low cost of nickel in the resulting product. [ABSTRACT FROM AUTHOR]

The present work demonstrates a sustainable approach of using relatively coarser iron ore particles for ironmaking. The motivation is to reduce the energy consumption in the milling of the iron ore by utilizing coarser iron ore particles (+0.05 mm) and to select a suitable binder for improving pellet properties. Iron ore fines in the range of 0.05–0.25 mm was selected and classified into three size ranges. Fluxed iron ore pellets were prepared using lime as a binder for the basicity of 0, 1, and 2. Reduction of these pellets with a packed bed of coal fines was performed in the temperature range of 900–1200 °C for a duration of 30–120 min. The direct reduction kinetics of the iron ore pellets were studied by employing diffusion and chemical reaction control models to the experimental data. The results show that pellets made with coarser iron ore particles have improved reduction behavior and kinetics. The reduction reaction is found to be a mixed control. The activation energy for the reduction reaction varies from 44.3 to 74.76 kJ mol−1 as iron ore particle size decreases from 0.25 to 0.05 mm and basicity increases from 0 to 2. [ABSTRACT FROM AUTHOR]

Abstract For the performance optimization strategies of hard carbon, heteroatom doping is an effective way to enhance the intrinsic transfer properties of sodium ions and electrons for accelerating the reaction kinetics. However, the previous work focuses mainly on the intrinsic physicochemical property changes of the material, but little attention has been paid to the resulting interfacial regulation of the electrode surface, namely the formation of solid electrolyte interphase (SEI) film. In this work, element F, which has the highest electronegativity, was chosen as the doping source to, more effectively, tune the electronic structure of the hard carbon. The effect of F‐doping on the physicochemical properties of hard carbon was not only systematically analyzed but also investigated with spectroscopy, optics, and in situ characterization techniques to further verify that appropriate F‐doping plays a positive role in constructing a homogenous and inorganic‐rich SEI film. The experimentally demonstrated link between the electronic structure of the electrode and the SEI film properties can reframe the doping optimization strategy as well as provide a new idea for the design of electrode materials with low reduction kinetics to the electrolyte. As a result, the optimized sample with the appropriate F‐doping content exhibits the best electrochemical performance with high capacity (434.53 mA h g−1 at 20 mA g−1) and excellent rate capability (141 mA h g−1 at 400 mA g−1).

The reduction of hematite with ammonia is a potentially environmentally friendly method of ironmaking. Previous studies on ammonia reduction of pellets typically involved samples weighing only 2.8 g and lacked detailed activation energy analysis for the ammonia-hydrogen co-reduction of pellets. Therefore, to further investigate the reduction thermodynamics and kinetics of NH3–H2 reduction of pellets, this study uses 50 g pellets for reduction experiments. By increasing the pellet mass, the study expands the scope of kinetic research on ammonia reduction of pellets. The results indicate that nitrogen gas produced from ammonia decomposition reduces the equilibrium components of the reducing gas. In the temperature range of 700–850 °C, the formation of iron nitride exhibits a narrow range during ammonia reduction of hematite. In the reduction of 50 g of pellets, the reduction rate using 100% NH3 is lower than that using a 50% NH3 and 50% H2 mixed gas, which is, in turn, slower than using 100% H2. As temperature increases, the reduction effect of 50% NH3 and 50% H2 approaches that of 100% H2. Among common gas-solid reaction mathematical models, the Phase-boundary-controlled model with the Contracting Cylinder Model is selected as the most plausible mechanistic function. For the reduction of 50 g of pellets, the activation energies for reactions using 100% NH3, 50% NH3 and 50% H2, and 100% H2 are 65.42, 54.37, and 29.17 kJ/mol, respectively. The decomposition of NH3 has a negative effect on the reduction of Fe2O3. XRD analysis and electron microscopy element line scanning show that Fe4N is formed during the reduction of Fe2O3 with 100% NH3. The use of a 50% NH3 and 50% H2 mixture significantly reduces the formation of Fe4N during the reduction of the pellets.

Hydrogen-based smelting reduction has received widespread attention as an important technology for realizing low-carbon development in hydrogen metallurgy. In this study, the thermodynamics of smelting reduction was firstly analyzed by using FactSage 8.1 thermodynamic software, on the basis of which smelting reduction experiments of iron oxides by using bottom-blown hydrogen were carried out. The experiments used oxidized pellets as experimental materials, and the effects of the reduction process were analyzed in terms of the reduction temperature, the reduction time, and the hydrogen flow rate. The experimental results show that under the experimental conditions of a temperature of 1550 °C and a hydrogen flow rate of 0.2 Nm3/h, the reduction rate of iron oxides in the process of reducing iron oxides by hydrogen is significantly faster in the first 10 min than after 10 min. The hydrogen utilization rate reached a maximum of 41.87%, then decreased continuously and finally maintained at about 20%. Using the method of model fitting, it was found that the hydrogen-based molten reduction conformed to the phase boundary reaction model (Gα=1−(1−α)1/2), the corresponding mechanism function is fα=2(1−α)1/2, where α stands for the reduction conversion, and the reaction rate constant k(T) is 2.37 × 10−4 s−1 under the experimental conditions.

On‐board methanol reforming is a practical solution to supply hydrogen for fuel cell vehicles (FCVs). For commonly employed Cu‐based reforming catalysts, activation has a profound influence on subsequent reaction performance. However, tailoring of this process at the reformer level has received little research attention. Herein, we present the dynamics of compact methanol reformers with Cu/ZnO/Al2O3 catalysts during in situ H2/N2 pre‐activation as a preliminary step of online catalyst activation by computational fluid dynamics simulations. Raising inlet temperatures or hydrogen fractions is demonstrated to accelerate activation while generating a high‐temperature band within the catalyst bed, which hampers effective activation. Increasing the reductant flow rates improves the homogeneity of activation thanks to enhanced convective heat and mass transfer. Notably, we revealed that inlet reductants exceeding 453 K trigger temperature runaway that may severely damage the reformer. These new insights will enlighten optimization of operation and control of on‐board methanol reforming for FCVs. [ABSTRACT FROM AUTHOR]

Redox kinetics of oxygen carrier in chemical looping is an important component for material preparation, reactor design and process demonstration. How to bridge the gap between the microscale density functional theory (DFT) and the macroscale redox kinetics and develop a first-principle-based theoretical model is still a challenge in the field of chemical looping. This study addresses this challenge and proposes a DFT-based microkinetic rate equation theory to calculate the heterogeneous kinetics of Fe 2 O 3 reduction by CO in chemical looping. Firstly, the DFT calculation is adopted to search the reaction pathways and to obtain the energy barriers of elementary reactions. Secondly, the DFT results are introduced into the transition state theory (TST) to calculate the reaction rate constants and build the rate equations of elementary surface reactions. Finally, by considering the bulk diffusion, a rate equation is developed to bridge the gap between the elementary surface reactions and the grain conversion. In the theory, the reaction mechanism obtained from DFT and kinetic rate constants obtained from TST are directly implemented into the rate equation to predict the reduction kinetics of oxygen carriers without fitting experimental data. The accuracy of the developed theory is validated by experimental data of two Fe 2 O 3 oxygen carriers obtained from the thermogravimetric analyzer (TGA). The microkinetic rate equation theory is based on the first principles calculation and can predict directly the redox kinetics of oxygen carriers without depending on the experimental kinetic data, therefore, it provides a powerful theoretical tool to screen the oxygen carrier materials and optimize the microstructure of oxygen carriers. [ABSTRACT FROM AUTHOR]

Generally, fossil carbon materials (coal, coke/char, and petroleum coke), biological carbon materials (charcoal, woodchips), and quartz from the earth's crust are sources of carbon and silica to synthesise silicon carbide (SiC) at temperatures between 2000 and 2200 °C. The study investigated the isothermal and non-isothermal kinetics of synthesising SiC from automotive shredder residues (ASR) and windshield glass of end-of-life-vehicle (ELVs) at 1300 °C, 1400 °C, and 1500 °C for 30 min. The kinetics of ASR and waste glass degradation were studied by relating the thermogravimetric data via the Coats–Redfern model. The reaction mechanism includes the rapid formation of a gaseous SiO intermediate, and carbon reduction of the SiO to SiC is reaction-rate-controlling. The understanding of kinetics inferred that the optimisation of SiC formation is entirely associated with the conversion of SiO2 to SiO vapour and their reaction with CO and carbon particles. The kinetic parameters of the degradation of mixed ASR and waste glass were determined, and the activation energy of mixed ASR and glass for non-isothermal conditions are 22.48 kJ mol−1, 2.97 kJ mol−1, and 6.5 kJ mol−1, and for the isothermal study to produce SiC is 225.9 kJ mol−1, respectively. The results confirmed that this facile way of synthesising SiC would conserve about 50% of chemical energy compared to the traditional way of producing SiC. A beneficial route of transforming the heterogenous ASR and glass wastes into SiC with economic and environmental benefits is recognised. [ABSTRACT FROM AUTHOR]

The understanding of oxide scale reduction mechanisms after microstructure transformation under different preheating conditions is incomplete. Herein, the reduction kinetics and microstructure transformations of hot rolled steel strip oxide scale during reduction (30% H2–N2) annealing are studied in detail using thermogravimetric and microstructure analyses, and mathematical modeling based on the gas–solid reaction. The results show that the rate‐determining steps of the reduction reaction are nucleation and growth of new phase between 500 and 600 °C, and gas–solid interface reactions between 700 and 800 °C. Microstructure transformation of the oxide scale occurs during the preheating process: at 500 °C, the eutectoid iron preferentially dissolves, and short‐range diffusion of Fe ions into adjacent Fe3O4 increases their content in the metal oxide; at 600 °C, nucleation and growth of Fe1 − yO occur, and some Fe3O4 precipitates and white α‐Fe are found in the Fe1 − yO layer, whereas the majority of the Fe3O4/iron eutectoid structure is retained; between 700 and 800 °C, the oxide scale forms outer and inner layers of Fe3O4 and Fe1 − yO, respectively. After preheating and reduction, the reduced products are porous iron over 500–600 °C, while porous and dense iron occur at 700 °C; dense iron forms as whiskers or granules between 700 and 800 °C. The surface quality of hot rolled steel strip after reduction annealing is subsequently improved as surface cracks are infilled by the newly formed dense iron. [ABSTRACT FROM AUTHOR]

Water-soluble spin probes were obtained from reduction-resistant sterically shielded pyrrolidine nitroxides by forming a 4,5-dicarboxy-1H-1,2,3-triazole fragment in the side chain by the Huisgen reaction of the azido group with acetylenedicarboxylic acid ester followed by hydrolysis. For the synthesized radicals, the reduction rate constants by ascorbate and the partition coefficient in an octanol—water system were determined. [ABSTRACT FROM AUTHOR]

The effect of different lower air inlet tube inclinations on the gas dynamics, including concentration, fluid flow profile, temperature, and heat transfer potency, to the bottom part of a rotary hearth furnace (RHF), were investigated. The lower air-inlet tube inclination was varied from 5° to 25° upwards with the horizontal to maximize the burner efficiency. The inlet tube configuration with the lower two air-inlet tubes inclined at 10° upwards emerged as the most efficient tube orientation in the present burner system. This air inlet configuration of the burner produced the maximum heat transfer efficiency in transferring the combustion heat produced in the freeboard region to the bottom pellet layer region. Moreover, it was also able to produce better CO post-combustion efficiency. [ABSTRACT FROM AUTHOR]

Chemical looping dry reforming of methane (CL-DRM) is a viable technology by converting CH4 and CO2 to various value-added products to achieve carbon neutrality. However, it is vital for the technology to find suitable oxygen carriers with high oxygen capacity and activity. La0.35Sr0.35Ba0.3Fe1-xCoxO3 perovskite-type oxides were proposed as oxygen carriers for CL-DRM. The oxygen (O2) release property and the kinetics of La0.35Sr0.35Ba0.3Fe1-xCoxO3 reduction by CH4 were investigated via thermogravimetric analysis, O2-temperature programmed desorption and then in a fixed-bed reactor. The O2 release process of La0.35Sr0.35Ba0.3Fe1-xCoxO3 OCs can be divided into two phases. The O2 release process and corresponding rate of OCs were facilitated due to the substitution of Fe with Co in B-site. The total amounts of O2 release for these OCs were enhanced about 1.5 times from 0.445 mmol/gOC to 0.706 mmol/gOC as Co atomic fraction in B-site changes from 0 to 1. The linear correlation for high temperature phase and a volcano-curve for low temperature phase was found for the correlations among total O2 release and Co content during the O2 release process. The reduction kinetics of CH4 over OCs was described using the Avrami–Erofe'ev model (A1.5 or A2). The values of apparent activation energy (Ea) for all OCs were obtained. The results indicated the best substitution proportion of Co in La0.35Sr0.35Ba0.3Fe1-xCoxO3 OCs can be set in the range of 0.2–0.4 to emerge the excellent redox performance. The kinetics models and parameters offer valuable information for CL-DRM reactor design and further development of OCs with different A or/and B-site modifications.

The objective of this study was to investigate the effect of pre-oxidation treatment on the hydrogen-rich reduction of Panzhihua ilmenite concentrate powder on the reduction kinetics and mechanisms. In this study, reduction processes of raw and pre-oxidized ilmenite concentrates reduced by H 2 /CO mixtures (H 2 /CO = 0.4 and H 2 /CO = 2.5) at 950, 1000, and 1050 °C were systematically investigated using a thermal analyzer. The hydrogen-rich reduction rate was accelerated by the pre-oxidation treatment of raw ilmenite concentrate and an increase in H 2 in H 2 /CO mixtures. The hydrogen-rich reduction of raw and pre-oxidized ilmenite concentrates can be divided into two stages according to the first derivatives of the reduction process: Fe3+ to Fe2+ and Fe2+ to Fe. The results of the research on the model function demonstrated that the reaction mechanism of raw and pre-oxidized ilmenite concentrates were three-dimensional diffusion models in the first stage. In the second stage, the reaction mechanism of the raw ilmenite concentrate was a phase boundary reaction model, and for the pre-oxidized ilmenite concentrate, it was a chemical reaction model. Furthermore, the apparent activation energies of both raw and pre-oxidized ilmenite concentrates under different reducing atmospheres were determined and compared. It was demonstrated that pre-oxidation treatment could effectively reduce the apparent activation energies of the reduction reaction. It is feasible to combine the advantages of the pre-oxidation treatment and hydrogen-rich reduction with a higher hydrogen ratio for the efficient reduction of Panzhihua ilmenite concentrate. • Hydrogen-rich reduction of raw and pre-oxidized ilmenite concentrates was studied. • Pre-oxidation of ilmenite is beneficial for accelerating hydrogen-rich reduction. • Increasing the H 2 content and temperature is conducive to the reduction process. • Hydrogen-rich reduction of both ilmenite concentrates can be divided into 2 stages. • The changing activation energies of the hydrogen-rich reduction were obtained. [ABSTRACT FROM AUTHOR]

A large number of studies have shown that oolitic hematite is an iron ore that is extremely difficult to utilize because of its fine disseminated particle size, high harmful impurity content and oolitic structure. To recover iron from oolitic hematite, we developed a novel multistage dynamic magnetizing roasting technology. Compared with traditional magnetizing roasting technologies, this novel technology has the following advantages: firstly, the oolitic hematite is dynamically reduced in a multi-stage roasting furnace, which shortens the reduction time and avoids ringing and over-reduction; secondly, the novel dynamic magnetizing roasting technology has strong raw material adaptability, and the size range of raw materials can be as wide as 0–15 mm; thirdly, the roasting furnace adopts a preheating-heating process, and the low-calorific value blast furnace gas can be used as the fuel and reductant, which greatly reduces the cost. The actual industrial production data showed that the energy consumption in the roasting process can be less than 35 kg of standard coal per ton of raw ore. The iron grade of the concentrate and iron recovery reached 65% and 90%, respectively.

The reduction kinetics of serial phase transitions of iron oxides during reduction to a metallized state with different modes of technical hydrogen supply has been studied and substantiated. The results of the pellets formation when 3-5 % molasses is added to the red mud as a binding reagent are presented. The dependences of the reduction rate of iron oxides on the hydrogen flow rate are obtained. Based on the results of the experiments, a kinetic model was constructed, and with the help of X-ray phase and spectral analysis, it was proved that the agglomerates formed after heat treatment received high strength due to the adhesion of reduced iron particles with red mud particles. The use of a new type of charge materials in melting units will reduce the amount of emissions and dust fractions, as well as increase the metal yield.

Reducibility and reduction kinetics of hardened pellets prepared from a novel, lean-grade multimetallic magnetite ore was investigated in the present study. The hardened pellets were reduced between the temperature range of 1223–1423 K for 30–120 min in a bed of non-coking coal. The highest reducibility and metallization of 80% and 92% were obtained at 1373 K at a reduction time of 120 min. The kinetic model "[(1 − α)−1/3 − 1]2 = kt" was found to be the best fit for the reduction of pellets. Activation energy calculated for the pellets was 165.38 kJ/mole. A metallization of up to 85% was achieved on pellets reduced at 1373 K for 90 min. [ABSTRACT FROM AUTHOR]

Chemical looping reforming of methane is a novel and effective approach to convert methane to syngas, in which oxygen transfer is achieved by a redox material. Although lots of efforts have been made to develop high-performance redox materials, a few studies have focused on the redox kinetics. In this work, the kinetics of SrFeO3−δ−CaO·MnO nanocomposite reduction by methane was investigated both on a thermo-gravimetric analyzer and in a packed-bed microreactor. During the methane reduction, combustion occurs before the partial oxidation and there exists a transition between them. The weight loss due to combustion increases, but the transition region becomes less inconspicuous as the reduction temperature increased. The weight loss associated with the partial oxidation is much larger than that with combustion. The rate of weight loss related to the partial oxidation is well fitted by the Avrami—Erofeyev equation with n = 3 (A3 model) with an activation energy of 59.8 kJ·mol−1. The rate law for the partial oxidation includes a solid conversion term whose expression is given by the A3 model and a methane pressure-dependent term represented by a power law. The partial oxidation is half order with respect to methane pressure. The proposed rate law could well predict the reduction kinetics; thus, it may be used to design and/or analyze a chemical looping reforming reactor. [ABSTRACT FROM AUTHOR]

Iron(III) (oxyhydr)oxide minerals with varying particle sizes commonly coexist in natural environments and are susceptible to both chemical and microbial reduction, affecting the fate and mobility of trace elements, nutrients, and pollutants. The size-dependent reduction behavior of iron (oxyhydr)oxides in single and mixed mineral systems remains poorly understood. In this study, we used microbial and mediated electrochemical reduction approaches to investigate the reduction kinetics and extents of goethite and hematite. We found that small particles were preferentially reduced relative to their large counterparts in single and mixed mineral systems regardless of microbial or electrochemical treatments, which is attributed to the combined effect of higher thermodynamic favorability and greater surface availability. In mixed mineral systems, small particles were reduced slightly faster, whereas large particles were reduced notably slower and less extensively than solely predicted from single mineral systems. Specifically, when reduced alone, small particles showed Fe(III) reduction rate constants that were 1.5- to 3.6-fold higher than large particles, while when reduced together, the reduction rate constants for small particles were 6- to 21-fold higher than the rate constants for large particles. These collective findings provide new insights into the pivotal role of nanoparticulate iron (oxyhydr)oxides in environmental redox reactions.

The non-isothermal reduction kinetics by hydrogen of CuAl spinel solid solution was investigated using H2 temperature-programmed reduction at different heating rates methodology. The reduction process consists of four stages in terms of the reduction degree (α), corresponding to the reduction of non-spinel Cu2+, easily reducible spinel Cu2+, hardly reducible spinel Cu2+ (I), and hardly reducible spinel Cu2+ (II). The activation energy was between 83.2 and 122.1 kJ mol−1 when α

Long duration energy storage (LDES) is an economically attractive approach to accelerating clean renewable energy deployment. The newly emerged solid oxide iron–air battery (SOIAB) is intrinsically suited for LDES applications due to its excellent low‐rate performance (high‐capacity with high efficiency) and use of low‐cost and sustainable materials. However, rechargeability and durability of SOIAB are critically limited by the slow kinetics in iron/iron‐oxide redox couples. Here the use of combined proton‐conducting BaZr0.4Ce0.4Y0.1Yb0.1O3 (BZC4YYb) and reduction‐promoting catalyst Ir to address the kinetic issues, is reported. It is shown that, benefiting from the facilitated H+ diffusion and boosted FeOx‐reduction kinetics, the battery operated under 550 °C, 50% Fe‐utilization and 0.2 C, exhibits a discharge specific energy density of 601.9 Wh kg–1‐Fe with a round‐trip efficiency (RTE) of 82.9% for 250 h of a cycle duration of 2.5 h. Under 500 °C, 50% Fe‐utilization and 0.2 C, the same battery exhibits 520 Wh kg–1‐Fe discharge energy density with an RTE of 61.8% for 500 h. This level of energy storage performance promises that SOIAB is a strong candidate for LDES applications. [ABSTRACT FROM AUTHOR]

Isothermal thermogravimetric analysis was used to study the reduction process of solid/liquid wustite by hydrogen. Results show that wustite in both states can be reduced entirely at all temperatures. The thermal and kinetic conditions for the hydrogen reduction of molten phases are better than those when the reactants and products are in the solid state, with a higher reaction rate. The hydrogen reduction of different wustite phases fits the Mampel Power model (power exponent n = 1/2) well, and this model is independent of the phase state. The average apparent activation energies of the reduction process calculated by the iso-conversional method are 5.85 kJ·mol−1 and 104.74 kJ·mol−1, when both reactants and products are in the solid state and the molten state, respectively. These values generally agree with those calculated by the model fitting method. [ABSTRACT FROM AUTHOR]

With Pd as an example, a set of quantitative analyses is designed to shed light on the bromide‐mediated reduction kinetics and oxidative etching in determining the twin structure and facet of Pd nanocrystals. The success of this work relies on the kinetic measurements of Pd(II) precursor reduction and the close examinations of resultant Pd seeds and nanocrystals at different stages of synthesis. We observe there is a clear trend where low, moderate, and high initial Pd(II) reduction rates regulated by Br− ions correspond to the formation of Pd seeds with singly‐twinned, multiply‐twinned, and single‐crystal structures in the nucleation stage, respectively. Our quantitative analyses also suggest the oxidative etching induced by oxygen/Br− pair can selectively remove the multiply‐twinned Pd seeds from the products in the growth stage while leaving behind singly‐twinned or single‐crystal Pd seeds for the evolution into Pd nanocrystals with well‐defined facets in high purity. The mechanistic insights obtained in this work can be extended to the synthesis of Pd@Pd−Pt core−shell nanocubes with high‐index facets, which can be used as excellent electrocatalysts and photocatalysts for hydrogen generation. [ABSTRACT FROM AUTHOR]

Red mud is a potential iron resource that needs to be urgently exploited and utilized. However, due to the properties of high alkalinity, fine particle size and complex mineral composition, the utilization of red mud is difficult. Focusing on red mud's prominent feature of high alkalinity, this paper studies the influence of NaOH content on the reduction kinetics of hematite, which is the main component of red mud. The results show that the conversion degree of hematite was strongly inhibited by NaOH, and the magnetization and specific magnetic susceptibility of reduction products was significantly decreased with the increase in NaOH content. Meanwhile, the results of the calculation of kinetics parameters demonstrate that the addition of NaOH did not affect the control step of the reduction of hematite, while it dramatically decreased the reduction rate of hematite. Moreover, thermodynamic analysis and SEM-EDS detection were conducted to uncover the inhibited mechanism of NaOH on the reduction of hematite, which indicated that sodium ferrite could be produced spontaneously under the experimental conditions and that it is hard for it to be further reduced by CO. Furthermore, the produced sodium ferrite formed a dense film, which covered the surface of the hematite particles, inhibiting the diffusion of CO and thereby hindering the reduction of the interior hematite. [ABSTRACT FROM AUTHOR]

Generally, fossil carbon materials (coal, coke/char, and petroleum coke), biological carbon materials (charcoal, woodchips), and quartz from the earth’s crust are sources of carbon and silica to synthesise silicon carbide (SiC) at temperatures between 2000 and 2200 °C. The study investigated the isothermal and non-isothermal kinetics of synthesising SiC from automotive shredder residues (ASR) and windshield glass of end-of-life-vehicle (ELVs) at 1300 °C, 1400 °C, and 1500 °C for 30 min. The kinetics of ASR and waste glass degradation were studied by relating the thermogravimetric data via the Coats–Redfern model. The reaction mechanism includes the rapid formation of a gaseous SiO intermediate, and carbon reduction of the SiO to SiC is reaction-rate-controlling. The understanding of kinetics inferred that the optimisation of SiC formation is entirely associated with the conversion of SiO2 to SiO vapour and their reaction with CO and carbon particles. The kinetic parameters of the degradation of mixed ASR and waste glass were determined, and the activation energy of mixed ASR and glass for non-isothermal conditions are 22.48 kJ mol−1, 2.97 kJ mol−1, and 6.5 kJ mol−1, and for the isothermal study to produce SiC is 225.9 kJ mol−1, respectively. The results confirmed that this facile way of synthesising SiC would conserve about 50% of chemical energy compared to the traditional way of producing SiC. A beneficial route of transforming the heterogenous ASR and glass wastes into SiC with economic and environmental benefits is recognised.

[Display omitted] • Formation of a solid product layer of MgF 2 /Be caused relatively low reduction rates. • Reduction is volume diffusion controlled with an activation energy of 66.01 kJ/mol. • 90.1 wt% Be extraction rate was achieved by lowering particle sizes of Mg and BeF 2. Beryllium (Be) is mainly produced by magnesiothermic reduction of beryllium fluoride (BeF 2). This research aims to improve the extraction rate of Be by investigating the reaction mechanism and kinetics during the magnesiothermic reduction of BeF 2. It was found that the solid product layer composed of MgF 2 and Be metal produced during the magnesiothermic reduction process is the main reason hindering the further improvement of the reduction rate. Kinetic study on the magnesiothermic reduction of BeF 2 shows that it was controlled by volume diffusion. An apparent activation energy of 66.01 kJ/mol was obtained for the magnesiothermic reduction in the temperature range of 850–950 °C. Aiming to extract Be from BeF 2 with a high efficiency, granular-shaped Mg (particle size 0.2–5 mm) and BeF 2 powder (particle size < 0.83 mm) were used as raw materials for magnesiothermic reduction at 900 °C for 30 min, protected using Ar atmosphere. This was followed by further heating to 1300 °C and holding for 10 min, and the highest extraction rate of Be was achieved at 90.1 wt% with the Be purity of 94.2 wt%. [ABSTRACT FROM AUTHOR]

Non-thermal hydrogen plasma is a novel reducing medium that can yield H2 derived species capable of improving the reduction efficiency of metallic oxides when compared to a conventional reduction by hydrogen gas. To analyze the morphological changes of the samples and evaluate the impact of the plasma hydrogen species on the kinetic process, this work performed Cu2O powder reduction by non-thermal hydrogen plasma and compared it to hydrogen gas reduction at the same experimental conditions. The experiments were conducted in a pulsed direct current glow discharge reactor at pressure of 533 Pa, varying temperatures between 250°C and 400°C and reduction time intervals from 5 to 120 min. The results show that hydrogen plasma reduction is a faster process, reaching a higher degree of metallization of the Cu2O powder than hydrogen gas process in any reduction condition. Hydrogen plasma promotes a higher sintering degree of the newly formed porous copper particulates than hydrogen gas processing. The kinetic assessment of experimental data shows that plasma process kinetics are best-fitted to Prout-Tompkins’ nucleation model at temperature range from 300°C to 400°C, and to Jander's diffusion model at 250°C. On the other hand, gas process kinetics are best adjusted to Prout-Tompkins’ and JMAEK's models at 400°C and 350°C, respectively. The calculated apparent activation energy of plasma reduction is 19.06 kJ/mol at temperature range of 300°C – 400°C; whilst for gas reduction is 73.79 kJ/mol at temperature range of 350°C–400°C.

Simple Summary: NADPH-cytochrome P450 reductase (CPR) enzymes are known to undergo an ample conformational transition between the closed and open states in the process of their redox cycling. To explore the conformational landscape of CPR from the potential biofuel crop Sorghum bicolor (SbCPR), we incorporated a FRET donor/acceptor pair into the enzyme and employed rapid scanning stop-flow and pressure perturbation spectroscopy to characterize the equilibrium between its open and closed states at different stages of the redox cycle. Our results suggest the presence of several open conformational sub-states differing in the system volume change associated with the opening transition (ΔV0). Although the closed conformation always predominates in the conformational landscape, the population of the open conformations increases by order of magnitude upon the two-electron reduction and the formation of the disemiquinone state of the enzyme. In addition to elucidating the functional choreography of plant CPRs, our study demonstrates the high exploratory potential of a combination of the pressure-perturbation approach with the FRET-based monitoring of protein conformational transitions. NADPH-cytochrome P450 reductase (CPR) from Sorghum bicolor (SbCPR) serves as an electron donor for cytochrome P450 essential for monolignol and lignin production in this biofuel crop. The CPR enzymes undergo an ample conformational transition between the closed and open states in their functioning. This transition is triggered by electron transfer between the FAD and FMN and provides access of the partner protein to the electron-donating FMN domain. To characterize the electron transfer mechanisms in the monolignol biosynthetic pathway better, we explore the conformational transitions in SbCPR with rapid scanning stop-flow and pressure-perturbation spectroscopy. We used FRET between a pair of donor and acceptor probes incorporated into the FAD and FMN domains of SbCPR, respectively, to characterize the equilibrium between the open and closed states and explore its modulation in connection with the redox state of the enzyme. We demonstrate that, although the closed conformation always predominates in the conformational landscape, the population of open state increases by order of magnitude upon the formation of the disemiquinone state. Our results are consistent with several open conformation sub-states differing in the volume change (ΔV0) of the opening transition. While the ΔV0 characteristic of the oxidized enzyme is as large as −88 mL/mol, the interaction of the enzyme with the nucleotide cofactor and the formation of the double-semiquinone state of CPR decrease this value to −34 and −18 mL/mol, respectively. This observation suggests that the interdomain electron transfer in CPR increases protein hydration, while promoting more open conformation. In addition to elucidating the functional choreography of plant CPRs, our study demonstrates the high exploratory potential of a combination of the pressure-perturbation approach with the FRET-based monitoring of protein conformational transitions. [ABSTRACT FROM AUTHOR]

Pyrrolidine nitroxides with four bulky alkyl substituents adjacent to N–O group are known for their high resistance to bioreduction. The 3,4-unsubstituted 2-tert-butyl-2-ethylpyrrolidine-1-oxyls were prepared from the corresponding 2-tert-butyl-1-pyrroline-1-oxides via either the addition of ethinylmagnesium bromide with subsequent hydrogenation or via treatment with ethyllithium. The new nitroxides showed excellent stability to reduction with ascorbate with no evidence for additional large hyperfine couplings in the EPR spectra. [ABSTRACT FROM AUTHOR]