Effective Reaction Rate Constants Research Articles

Gas Phase Reaction of Ketene with H2S in Troposphere: Catalytic Effects of Water and Ammonia

Background: Additions of water monomer (H2O) to simplest ketene, i.e., H2C=C=O (mentioned as ketene, henceforth) in the Earth's atmosphere results in the formation of acetic acid. However, this reaction is not feasible under tropospheric conditions due to the high reaction barrier amounting to nearly 40 kcal mol-1. A Significant reduction of the barrier height (below 20 kcal mol-1) is achieved upon addition of another H2O molecule as a catalyst. It is worth mentioning that like H2O and ammonia (NH3), H2S could also play an important role in the “loss mechanism” of various atmospherically important species such as ketones and aldehydes. Aims: This study aims to get insight into the energetics and kinetics of a reaction between ketene and H2S in the troposphere which has not been done before. Objective: Due to close similarity of H2O and H2S, studying the sulfolysis reaction between ketene and H2S could provide some interesting insights into the nature of various hydrogen bonded complexes of ketene as well as the impact on the products formed under the atmospheric conditions. Methods: The water and ammonia catalyzed gas-phase addition reactions of ketene with H2S has been investigated using CCSD(T)-F12a/cc-pVTZ-F12a//M06-2X/6-311++G** level of theory. In this study, rate constants for all possible reaction channels are calculated using transition state theory. Results: It is found that, under tropospheric conditions at 298 K and 1 atm, the rates via catalyzed reaction channels are significantly faster than those via uncatalyzed reactions. Between the two catalysts, ammonia acts as far better catalyst than water for this reaction. However, since the concentration of water is significantly larger than ammonia, the effective rate of water catalyzed reaction becomes higher than that of ammonia catalyzed reaction. Combustion is a major source of ketene in atmosphere. Under combustion conditions such as in the presence of air and at or above ignition temperature, the ammonia catalyzed channel is faster below 1500 K, while the uncatalyzed reaction channel becomes faster above that temperature. Conclusion: Results from the present study show that the barrier for thioacetic acid formation through uncatalyzed sulfolysis of ketene via faster C=O addition pathway is substantially high as 40.6 kcal mol-1. The barrier height of the two transition states TS1 and TS2 are 19.7 and 13.8 kcal mol-1 for water catalyzed reaction and 14.4 and 7.2 kcal mol-1 for ammonia catalyzed reaction. Thus, ammonia has appreciably lowered the barrier height compared to water as catalyst. It has been observed that the hydrolysis reaction is more probable than the sulfolysis reaction under atmospheric conditions in the troposphere, but the ammonia catalysed sulfolysis is the fastest one at 298 K. The effective rate constant of the water catalysed hydrolysis reaction is found to be more than the ammonia catalysed reaction due to the higher monomer concentration of water than ammonia. Ammonia catalyzed reaction rate increases monotonously with increasing temperature. Further rate coefficient for uncatalyzed reaction is found to be dominant under combustion conditions, i.e., above 1500 K.

GAS DISCHARGES AS A TOOL FOR CLEANING GAS AND SOLUTION MEDIUMS AND SYNTHESIS OF INORGANIC MATERIALS

The article provides an overview of the results of research of the purification processes of gas and solution media from organic (tetrachloromethane, 1,4-dichlorobenzene and 2,4-di-chlorophenol, etc.) and inorganic (Cr(VI), Mn(VII), Cu2+, Fe2+3+, Zn2+, Cd2+, Ni2+, etc.) substances, as well as the synthesis of oxide materials based on the above metals under the action of a dielectric barrier discharge (DBD) and atmospheric pressure DC discharge. The work was carried out in joint research conducted at the Departments of Industrial Ecology and Microelectronic Devices and Materials of the ISUCT over the past 10 years. As a result of the research, the kinetic regularities of decomposition of the above organic substances were revealed, i.e. the rate and effective rate constants of the decomposition reactions and their dependences on the DBR parameters (power, gas and solution flow rates) were determined. On the basis of these data, the energy efficiency of decomposition processes was found. The main decomposition products and their dependence on the discharge parameters are determined. Probable mechanisms of the ongoing processes were proposed. It is shown that the action of a direct current discharge on aqueous solutions leads to the reduction of Cr(VI) and Mn(VII) in the composition of Cr2O72- and MnO4- to Cr3+ and Mn2+ ions. When the same discharge acts on solutions of salts containing Cu2+, Fe2+3+, Zn2+, Cd2+, Ni2+ ions, the formation of colloidal solutions of hydroxo compounds of these ions is observed. The sizes of resulting particles, their phase and chemical composition were determined by DLS, SEM, EDX, TGA, XRD, DSC methods. It is shown that the calcination of the obtained particles leads to the formation of crystalline oxides of the corresponding metals. Thus, the action of the discharge ensures the purification of aqueous solutions from heavy metals with the formation of oxide materials of the nanoscale range, which have semiconductor and catalytic properties. For citation: Guschin A.A., Grinevich V.I., Kvitkova E.Yu., Gusev G.I., Shutov D.A., Ivanov A.N., Manukyan A.S., Rybkin V.V. Gas discharges as a tool for cleaning gas and solution mediums and synthesis of inorganic materials. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 7. P. 120-131. DOI: 10.6060/ivkkt.20236607. 6835j.

Novel 3D analysis of reduction behavior of single iron-oxide particle in CO-CO2 gas atmosphere

The production of steel, which is achieved by the reduction of iron ores mainly through indirect reduction reactions in a blast furnace, is gradually increasing worldwide. Because the reducing gas diffuses three-dimensionally, irregular particle shapes influence the reduction through differences in the diffusion length. The analysis of actual irregularly shaped iron-ore particles using existing models is difficult because they are primarily effective for 1D systems. Therefore, a novel reduction model based on the 3D diffusion equation that accommodates irregular particle shapes and 3D systems was developed in this study. The established model was validated by reproducing experimental conditions and comparing the quantified effective diffusivity and chemical reaction rate constant using the shrinking core model. In addition, the model was used to investigate the reducing behavior of an actual sintered-ore particle and the effects of particle sphericity and macro pore content. The sintered-ore particle had a higher reduction rate than that of a spherical equivalent with the same volume because sections of the surface with shorter diffusion lengths facilitated the gas diffusion. Additionally, the particle sphericity was determined to be inversely proportional to the reduction rate because the rate of gas diffusion into the particle depended on the diffusion length. With respect to porous particles, the gas was found to readily diffuse into the particles through pores, leading to a higher reduction rate for higher pore numbers. Overall, the gas diffusion was confirmed to drive the reduction reaction.

NEW METHOD OF KINETIC MODELING OF ETHYLENE OXIDATION REACTION TO ETHYL ALCOHOL AND ACETALDEHYDE BY HYDROGEN PEROXIDE ON THE PER-FTPhPFe3+OH/Al2O3

The process of biomimetic monooxidation of ethylene into ethyl alcohol and acetaldehyde by hydrogen peroxide on the per-FTPhPFe3+OH/Al2O3 bioimitator, which showed high activity and unique resistance to the action of high-active intermediate reaction products was investigated. As a result of studying the kinetic regularities of the selective biomimetic oxidation of ethylene by hydrogen peroxide, a coherent-synchronized nature of the reaction was observed, consisting of two reactions: 1) primary (catalase) and 2) secondary (monooxygenase and peroxidase) reactions. A new approach to the kinetic modeling based on the determinant equation and coherence correlation of catalase-monooxygenase and catalase-peroxidase reactions coherently synchronized with each other was developed. The kinetic model of the process was developed on the basis of the determinant equation, which allows assessing the coherent nature of synchronously flowing reactions both qualitatively and quantitatively. Effective rate constants of catalase, monooxygenase and peroxidase reactions were determined based on this model as well as their effective activation energies were calculated.

Effect of formic acid on O2 + OH˙CHOH → HCOOH + HO2 reaction under tropospheric condition: kinetics of cis and trans isomers.

Formic acid (HCOOH) is one of the highly abundant acids in the troposphere. It is important in the formation of atmospheric aerosols and impacts the acidity of rainwater. In the present scenario, the model chemistry of HCOOH(FA) sources and sinks is poorly understood. In this work, we apply quantum chemical methods coupled with advanced statistical rate theories to understand the production of FA and its catalytic behavior under tropospheric conditions. The potential energy surfaces (PES) for O2 + OH˙CHOH and O2 + OH˙CHOH(+FA) reactions were constructed using the CCSD(T)/6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd) level and rate constants for the production of FA were predicted using Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation (ME) simulation with Eckart tunnelling and canonical variational transition state theory (CVT) with small curvature tunnelling (SCT) between the temperature range of 200-320 K and pressure range of 0.001 to 10 bar. The reaction follows the formation of cis and trans intermediates followed by spontaneous decomposition via concerted HO2 elimination to form stable post intermediates, which then leads to the straight formation of cis and trans formic acid. The current study also helps understand the role of cis and trans contribution to the total rate constants. The results show that O2 + OH˙CHOH is dominated by both cis and trans isomers; however, the trans isomer plays a more important role in the catalytic reaction. This result is due to the formation of a strong hydrogen-bonded complex in the trans isomer, which is dominated by the enthalpy factor rather than the entropy factor. The results predict that the catalytic effect of FA on the O2 + OH˙CHOH reaction is important when the concentration of FA is not included in the calculations; however, it has no effect under tropospheric conditions, when the FA concentration is included in the calculation. As a result, the total effective reaction rate constants are smaller. This work provides experimental/theoretical confirmation of Franco et al. who predicted that methanediol is the precursor for the FA formation, resolving an open problem in the kinetics of the gas phase reaction. O2 + OH˙CHOH and O2 + OH˙CHOH(+FA) probably explain other diol systems, which can help explain the formation of other atmospheric acids that affect aerosol formation and cloud evolution.

Hydrolysis and aminolysis of aldehydes catalyzed by water and amines: Formation of diols/aminol and the implication to atmospheric particle formation

The hydrolysis and aminolysis reactions of aldehydes were proved to be associated with the secondary organic aerosols (SOA) in the atmosphere. However, these reactions are forbidden owing to the high energy barriers. To make these reactions feasible and assess the catalytic ability of water molecules and amines, the hydrolysis and aminolysis of glyoxal (GL) and glycolaldehyde (GA) were investigated using quantum chemical calculations. The results show that water molecules and amines can catalyze effectively the hydrolysis and aminolysis of aldehydes and the catalytic ability of water molecules is stronger than that of methylamine (MA) and dimethylamine (DMA). Glycine (Gly) can play a stronger role than water molecules in the GL/GA hydrolysis and aminolysis reactions owing to the carboxyl group. At low relative humidity and high pollution condition, the effective rate constants of Gly-catalyzed reactions can be comparable to that of water-catalyzed reactions. The results of MD simulations indicate that the products of GL/GA hydrolysis and aminolysis can participate in the new particle formation (NPF) involving sulfuric acid (SA).

EFFECT OF THE COMPOSITION OF A MANGANESE-CONTAINING POLYMER CATALYST ON THE KINETICS OF THE OXIDATION REACTION OF N-HEPTANE WITH MOLECULAR OXYGEN

Catalysts with manganese nanoparticles (5 and 10 wt %) immobilized on poly-4-vinylpyridine were prepared. When interacting with molecular oxygen, the catalyst forms active oxygen, which is involved in the low-temperature oxidation of n-heptane. These catalyst compositions have been used to oxidize n-heptane with pure oxygen to give alcohols, aldehydes and ketones. Oxidation of n-heptane was carried out in the temperature range 303-383 K, molar ratios of heptane:oxygen = 1:3.38, and at atmospheric pressure. It has been found that the non-crosslinked (MnP4VP polymer poly-4-vinylpyridine) and N,N-methylene-bis-acrylamide-crosslinked MnP4VP/MBAA metal-polymer catalyst containing 5 wt % Mn2+ exhibits the highest activity in n-heptane oxidation reactions. The kinetic parameters of the reaction of n-heptane oxidation with oxygen at low temperatures were studied using a kinetic model based on the heptane conversion data. The kinetic model was compiled on the basis of experimental data: heptane:oxygen = 1:3.38 at atmospheric pressure using Mn (wt. 5%) P4VP/MBAA in the temperature range 303-383 K. Within the framework of the chosen kinetic model effective rate constants of the oxidation reaction with the formation of alcohols was calculated

КІНЕТИЧНІ ДОСЛІДЖЕННЯ ТА МОДЕЛЮВАННЯ ПРОЦЕСУ ЕСТЕРИФІКАЦІЇ БЕНЗОЙНОЇ КИСЛОТИ

The kinetic regularities of benzoic acid esterification with 1-butyl alcohol catalyzed by p-toluenesulfonic acid under stationary conditions have been studied. The study shows that the reaction has the first order with respect to benzoic acid. It is proposed a method for calculating the forward and reverse reaction constants, and the equilibrium constant using the determined effective rate constant of the esterification reaction. The preexponential factors and activation energies of the forward and reverse reactions as well as the thermal effect and the entropy change of the esterification reaction have been calculated. In particular, the thermal effect of benzoic acid esterification reaction with 1-butyl alcohol at a temperature of 365.2–389.4 K is 622 J∙mol-1, and the activation energies of the forward and reverse reactions are 58.40 and 57.70 kJ∙mol-1, respectively. The calculated kinetic characteristics of the esterification reaction were used in mathematical modeling of the butyl benzoate obtaining process under nonstationary conditions. Taking into account the kinetic characteristics of the reactions and the stages peculiarities of the butyl benzoate obtaining process the calculation of the change in the benzoic acid conversion over time was performed. The study shows that under optimal conditions the benzoic acid conversion in 120 min reaches 92 %. The use of the experimental results and the created mathematical model of benzoic acid esterification process with 1-butyl alcohol makes it possible to calculate of kinetic curves of the reagent consumption under nonstationary conditions. The experimentals can be used to improve the technological process of the butyl benzoate manufacture in the industry.

Effect of Water and Formic Acid on ·OH + CH4 Reaction: An Ab Initio/DFT Study

In this work, we used ab initio/DFT method coupled with statistical rate theory to answer the question of whether or not formic acid (HCOOH) and water molecules can catalyze the most important atmospheric and combustion prototype reaction, i.e., ·OH (OH radical) + CH4. The potential energy surface for ·OH + CH4 and ·OH + CH4 (+X) (X = HCOOH, H2O) reactions were calculated using the combination of hybrid-density functional theory and coupled-cluster theory with Pople basis set [(CCSD(T)/ 6-311++G(3df,3pd)//M06-2X/6-311++G(3df,3pd)]. The results of this study show that the catalytic effect of HCOOH (FA) and water molecules on the ·OH + CH4 reaction has a major impact when the concentration of FA and H2O is not included. In this situation the rate constants for the CH4 + HO···HCOOH (3 × 10−9 cm3 molecule−1 s−1) reaction is ~105 times and for CH4 + H2O···HO reaction (3 × 10−14 cm3 molecule−1 s−1 at 300 K) is ~20 times higher than ·OH + CH4 (~6 × 10−15 cm3 molecule−1 s−1). However, the total effective rate constants, which include the concentration of both species in the kinetic calculation has no effect under atmospheric condition. As a result, the total effective reaction rate constants are smaller. The rate constants when taking the account of the FA and water for CH4 + HO···HCOOH (4.1 × 10−22 cm3 molecule−1 s−1) is at least seven orders magnitude and for the CH4 + H2O···HO (7.6 × 10−17 cm3 molecule−1 s−1) is two orders magnitude smaller than ·OH + CH4 reaction. These results are also consistent with previous experimental and theoretical studies on similar reaction systems. This study helps to understand how FA and water molecules change the reaction kinetic under atmospheric conditions for ·OH + CH4 reaction.

Water Splitting and Transport of Ions in Electromembrane System with Bilayer Ion-Exchange Membrane.

Bilayer ion-exchange membranes are mainly used for separating single and multiply charged ions. It is well known that in membranes in which the layers have different charges of the ionogenic groups of the matrix, the limiting current decreases, and the water splitting reaction accelerates in comparison with monolayer (isotropic) ion-exchange membranes. We study samples of bilayer ion-exchange membranes with very thin cation-exchange layers deposited on an anion-exchange membrane-substrate in this work. It was revealed that in bilayer membranes, the limiting current’s value is determined by the properties of a thin surface film (modifying layer). A linear regularity of the dependence of the non-equilibrium effective rate constant of the water-splitting reaction on the resistance of the bipolar region, which is valid for both bilayer and bipolar membranes, has been revealed. It is shown that the introduction of the catalyst significantly reduces the water-splitting voltage, but reduces the selectivity of the membrane. It is possible to regulate the fluxes of salt ions and water splitting products (hydrogen and hydroxyl ions) by changing the current density. Such an ability makes it possible to conduct a controlled process of desalting electrolytes with simultaneous pH adjustment.

Heterogeneous oxidation of isoprene SOA and toluene SOA tracers by ozone

Secondary Organic aerosols (SOA) are important components of PM 2.5. In order to control the heavy haze pollution, it is essential to find out the contributions of main SOA precursors. Nowadays, the tracer-based method has been widely used in analyzing the contributions of the precursors to SOA. However, it is not well known that whether the SOA tracers can be oxidized or how the instability of the SOA tracers would influence the accuracy of the tracer-based method for source apportionment.In this paper, the heterogeneous oxidation experiments of SOA tracers produced from isoprene and toluene as well as their mixtures under different conditions were conducted in a 2 m3 indoor chamber. The relative rate constants approach was used to determine the effective rate constants of the ozone reactions of the tracers. Concentrations of 2-Methyl Erythritol, a tracer of isoprene SOA, and 2, 3-Dihydroxy-4-oxopentanoic Acid, a tracer of toluene SOA, were analyzed using GC-MS. The effects of different seed aerosols and initial VOC0/NO on the heterogeneous oxidation of the tracers were investigated. The effects of co-existing components in the SOA produced from the mixture of isoprene and toluene on the heterogeneous oxidation of the tracers by ozone were also studied.

Electrochemical characteristics of heterogeneous bipolar membranes and electromembrane process of recovery of nitric acid and sodium hydroxide from sodium nitrate solution

Frequency spectra of electrochemical impedance and current-overvoltage characteristics of an MB-2m bipolar membrane containing ion-polymer with catalytically active phosphoric acid groups in water dissociation reaction, and industrial MB-1, MB-2, and MB-3 bipolar membranes were studied in a system containing nitric acid and sodium hydroxide solutions. It is shown that the electrical resistance and overvoltage of bipolar region in the modified MB-2m and industrial MB-3 membranes are close and significantly lower than in industrial MB-1 and MB-2membranes. The effective rate constants of catalytic reaction of water dissociation are determined in the studied membranes. The process of producing nitric acid and sodium hydroxide from sodium nitrate with the modified MB-2m bipolar membrane and industrial MB-1 and MB-3 bipolar membranes was studied. It is shown that the use of the MB-2m bipolar membrane allows producing nitric acid and sodium hydroxide with higher concentrations, current efficiencies, specific productivity, lower specific energy consumption, and degree of sodium nitrate contamination than in the case when using industrial MB-1 and MB-3 membranes.

ЗАСТОСУВАННЯ МОДЕЛІ ДЕРЕВОПОДІБНОЇ ПОРИСТОЇ СТРУКТУРИ ДЛЯ ОЦІНКИ ТЕМПЕРАТУРИ ЗАЙМАННЯ ЧАСТИНКИ ВУГЛЕЦЕВОГО ЗАЛИШКУ

A model of a tree-like porous structure has been used to calculate the thermal effects of chemical reactions of the molecular oxygen and carbon dioxide with an accessible particle surface of a carbon residue and to estimate heat balance with a gas environment. The effective reaction rate constant of the oxygen and carbon dioxide for the contour surface of the particle has been presented as the averaged value of the effective constants for the components of the surface of the carbon residue partricle: the inlets in the micro-, meso-, macropores; the density of outer surface; the areas of mineral impurities. The model takes into account: the volume fractions of micro-, meso-, macropores and mineral impurities in the carbon residue; the ratio of the length and radius of the pores; Knudsen diffusion in the pores; the density of branches on the surface of the transport pores; the reaction rate constant on dense carbon surface; limiting the reaction rate in the pores by the amount of chaotic flow of reagent molecules into the inlet. The external mass transfer of the carbon residue particle has been taken into account in the model of the surface layer. This factor depends on the particle diameter and the steady velocity in the gaseous environment. When calculating the heat balance of the particles, the thermal effect of chemical reactions of the oxygen and carbon dioxide with carbon, convective heat exchange with the gaseous environment and heat loss due to radiation have been taken into account. In the stationary model, the ignition temperature of carbon residue particles in a gaseous environment containing the oxygen and carbon dioxide as components have been calculated. It has been shown that the parameters of the porous structure significantly effect on the ignition temperature and the equilibrium temperature of the particle in the flue gases. The dependence of the ignition temperature of the particles on the value of the available surface of the carbon residue has been obtained.

Thermal Study on Stabilizing the Combustion Front via Bimetallic Mn@Cu Tallates during Heavy Oil Oxidation

Metal tallates are generating a considerable interest as catalysts for thermaly enhanced oil recovery. Meanwhile, In-situ combustion is considered a promising thermally enhanced oil recovery method, it is still viewed as a complicated process due to its multiphasic, multicomponent and multistep reactions occurring within it. In this study we investigated the impact of Mn@Cu tallate on heavy oil oxidation process in order to highlight its effect on stabilizing combustion front using differential scanning calorimetry combined with isoconversional principle for calculating the kinetic parameters of the process. The obtained data have showed that Mn@Cu tallate can play an important role in stabilizing combustion front of in-situ combustion where it decreased the energy of activation of low temperature (LTO) and high temperature oxidation (HTO) regions. As a result, the effective reaction rate constants in both regions increased respectively as well.

SPECTRAL INVESTIGATIONS OF COBALT PORPHYRINATES INTERACTION WITH RADICAL POLYMERIZATION INITIATORS

The article presents the results of the kinetics study of the cobalt porphyrins interaction with radical polymerization initiators – benzoyl peroxide and lauryl peroxide – in solution by the spectrophotometric method. From disparate literature data, it is known that some metalloporphyrins can interact with benzoyl peroxide to form the tautomers of porphyrins – isoporphyrins. These compounds have a number of specific properties, for example, it can be catalysts of various processes. Perhaps the isoporphyrins formation is the reason for high activity of the initiating systems “cobalt porphyrin – benzoyl peroxide” in the polymerization of vinyl monomers. Cobalt(II)complexes of tetraphenylporphyrin, tetra-para-methoxyphenylporphyrin, 5,15-bis(4´-tert-butylphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetra-p-butylporphyrin were selected as the objects of this study. The influence of the porphyrin ligand structure on the formation of cobalt isoporphyrins was estimated. The interaction of cobalt (II) tetraphenylporphyrin and cobalt (II) tetra-para-methoxyphenylporphyrin with peroxides showed changes in the electronic absorption spectra of metalloporphyrins: deformation of the Soret band, reduction of the absorption band in the visible region, and the appearance of absorption bands in the near IR region. These changes are characteristic for metalloisoporphyrins. Data on the interaction of cobalt porphyrins with lauryl peroxide were obtained for the first time. The formation of isoporphyrins is possible with the different ratio of concentrations of reagents: with a lack of peroxide, with equimolar ratio, and also with a significant (100-fold) excess of peroxide. When 5,15-bis (4´-tert-butylphenyl)-3,7,13,17-tetramethyl-2,8,12,18-tetra-p-butylporphyrinate cobalt (II) reacted with peroxides, no isoporphyrinates were observed. The article presents the effective reaction rate constants of the cobalt isoporphyrinates formation at 25 °C. It is shown that the structure of both cobalt porphyrinates and organic peroxides affects the possibility and rate of isoporphyrins formation.

Improved Gas–Solids Mass Transfer in Fluidized Beds: Confined Fluidization in Chemical-Looping Combustion

© 2019 American Chemical Society. Fluidized bed processes with reactive bed material have become increasingly popular as research topics, with applications such as chemical-looping technologies, oxygen carrier aided combustion, and fluidized bed gasification being extensively investigated. When used at commercial scale the performance of such processes may be limited not by gas-solid reactivity, but by mass transfer of reactants from bubbles to the emulsion phase. In an effort to break down the two-phase flow structure, and thereby increase the bubble-emulsion mass transfer coefficient, spherical packing material was added to a fluidized bed using ilmenite as bed material. Two types of packing were tested: expanded clay aggregate (ECA) and aluminum silicate balls (ASB). Both packings had a diameter of about 12 mm but drastically different bulk densities of 240 kg/m 3 and 1400 kg/m 3 , respectively. These were tested in chemical-looping-combustion batch experiments using a stainless-steel reactor with a diameter of 78 mm, with syngas or carbon monoxide as fuel at 915 °C. The lighter packing formed a floating plug while the heavier remained stationary at the reactor bottom. To compare the confined fluidized bed to a reference conventional one, a simple reaction model was implemented based on the experiments. It showed that in the confined fluidized bed the associated effective reaction rate constant increased by up to a factor of 2 for a given bed mass. Further, up to 4 times less oxygen carrier bed mass was needed to achieve the same gas conversion, at a lower total pressure drop. Experiments with only carbon monoxide showed similar gains when using aluminum silicate balls, indicating that catalysis of the water gas shift reaction was not the main factor for improved gas conversion. It can be concluded that the concept of confined fluidization has great potential to increase mass transfer in fluidized beds with active bed material.

Effects of water, ammonia and formic acid on HO2 + Cl reactions under atmospheric conditions: competition between a stepwise route and one elementary step.

Quantum chemical calculations at M06-2X and CCSD(T) levels of theory have been performed to investigate the effects of H2O, NH3, and HCOOH on the HO2 + Cl → HCl + O2 reaction. The results show that catalyzed reactions with three catalysts could proceed through two different mechanisms, namely a stepwise route and one elementary step, where the former reaction is more favorable than the latter. Meanwhile, for the stepwise route, a single hydrogen atom transfer pathway in the presence of all catalysts has more advantages than the respective double hydrogen atom transfer pathway. Then, the relative impacts of catalysts under tropospheric conditions were investigated by considering the temperature dependence of the rate constants and the altitude dependence of catalyst concentrations. The calculated results show that at 0 km altitude, the HO2 + Cl → HCl + O2 reaction with catalysts, such as H2O, NH3, or HCOOH, cannot compete with the reaction without a catalyst, as the effective rate constant with a catalyst is smaller by 2–6 orders of magnitude than the naked reaction within the temperature range 280–320 K. The calculated results also show that at altitudes of 5, 10 and 15 km, the effective rate constant of the HCOOH-catalyzed reaction increases obviously with an increase in altitude. At 15 km altitude, its value is up to 9.63 × 10−11 cm3 per molecule per s, which is close to the corresponding value of the reaction without a catalyst, showing that the contribution of HCOOH to the HO2 + Cl → HCl + O2 reaction cannot be neglected at high altitudes. The new findings in this investigation are not only of great necessity and importance for elucidating the gas-phase reaction of HO2 with Cl in the presence of acidic, neutral and basic catalysts, but are also of great interest for understanding the importance of other types of hydrogen abstraction in the atmosphere.

Determination of Effective Surface Area and Reaction Rate Constant By Cyclic Voltammetry Considering Ohmic Resistance and CPE Effects

One of the most commonly used electroanalytical techniques for determining the effective surface area and reaction rate constant in a redox system is linear sweep voltammetry due to its sensitive response to a reaction and easy implementation. In linear sweep voltammetry, a linear potential scan is applied to an immobile electrode submerged in an unstirred analyte. The responses to the applied potential is the total current which consists of the faradaic and non-faradaic currents. The faradaic current is the current generated by the reaction of interest, while the non-faradaic current is generated by an electrical double layer. As the faradaic processes received high attention in modeling [1-3], the non-faradaic current, which can be described by the constant phase element (CPE), received less attention. The conventional approach to evaluate the effective surface area and reaction rate constant is to assume that the non-faradaic current is linear and the ohmic drop is negligible. For a quasireversible reaction, by extrapolating the baseline, the peak current and potential are obtained and applied to the relation of Matsuda and Ayabe [4] and Nicholson’s method [5] to determine for the effective surface area and the reaction rate constant, respectively. However, this conventional approach could lead to an inaccurately estimated peak current and potential since the non-faradaic current is not always linear and the ohmic drop, which results in the peak potential shifting, occasionally cannot be negligible. In addition, the faradaic and non-faradaic currents are coupled through ohmic drop effects. Our research group has successfully developed numerical modeling of voltammetry, including the combined effects of ohmic resistance, CPE, mass transfer, and faradaic processes [6]. In this model, the CPE parameters, i.e. the pseudo-capacitance and the dispersion coefficient, are required as inputs. Generally, the CPE parameters were evaluated by electrochemical impedance spectroscopy (EIS). However, the EIS analysis is time-consuming and requires prior knowledge about the equivalent circuit of a system to obtain the CPE parameters. Furthermore, it measures only impedance of a system at one specific potential in frequency domain, while a voltammetry method is a potentiodynamic measurement, which operates under a wide potential window. Therefore, the semi-theoretical approach is introduced to evaluate the CPE parameters under voltammetry condition. This approach possesses several advantages for evaluating the CPE parameters, such as time-saving, simple, and straightforward. In this study, by considering the effects of ohmic resistance and CPE, an approach for determining the electrode effective surface area and reaction rate constant using linear sweep voltammetry was developed. By fitting the peak current and potential of the numerical simulation to those of the experimental data (see Fig. 1a), the electrode effective surface area and reaction rate constant can be determined. As the non-faradaic current becomes relatively more important at faster scan rates, it is difficult to extrapolate the baseline, as depicted in Fig. 1b. This difficulty could lead to underestimation of the effective surface area since the relation of Matsuda and Ayabe, needs the faradaic peak current as an input. Furthermore, Nicholson’s method, which evaluates the reaction rate constant directly from the peak separation, would underestimate the reaction rate constant if the ohmic drop effect was appreciable. Therefore, owing to the problem that the non-faradaic current and ohmic drop effect occasionally could not be avoided, using our approach that takes them into consideration would lead to more accurate prediction of such parameters. Acknowledgment The authors would also like to express their gratitude to the Ministry of Education, Culture, Sports, Science and Technology, Japan, for providing financial support under the scholarship program for foreign students.

Dynamic surface composition in a Mars-van Krevelen type reaction: CO oxidation on Au/TiO2

Aiming at a better mechanistic understanding of Mars-van Krevelen type catalytic reactions, we have systematically investigated possible correlations between the composition of the reaction gas atmosphere, the concentration of surface oxygen vacancies (surface oxidation state), and the catalytic activity of a Au/TiO2 catalyst in the CO oxidation reaction. In the meantime, there is considerable experimental and theoretical evidence that this reaction follows a Au-assisted Mars-van Krevelen mechanism at reaction temperatures ≥80 °C. Employing quantitative pulse experiments in a temporal analysis of products (TAP) reactor we found that both the surface oxidation state and the activity of the catalyst under steady-state conditions depend sensitively on the composition of the reaction gas atmosphere, specifically on the CO:O2 ratio, and that there is a strict correlation between these quantities. A simple kinetic model is introduced, which allows to quantitatively determine the ratio of the effective reaction rate constants for reduction and oxidation of the TiO2 support surface. These results and ideas are considered to be of general relevance for the understanding of Mars-van Krevelen type reactions and specifically of oxidation reactions on supported Au catalysts, and they lend further support to previous proposals of a Au-assisted Mars-van Krevelen mechanism for this reaction.

Iminodiacetic acid synthesis over Cu/ZrO2 catalyst in a microchannel flow reactor

Flow microchannel reactor was used to study the synthesis of iminodiacetic acid (IDA) via the catalytic oxidative dehydrogenation of diethanolamine (DEA) over catalyst Cu/ZrO2 (containing copper in amount of 10mass%) at various residence times, reaction temperature ranging within 160–190°C. IDA was shown to form in the course of two consecutive reactions through intermediate compound N-(2-hydroxyethyl)glycine (HEG). DEA conversion and IDA yield were found to increase as residence time and reaction temperature grow, meanwhile HEG concentration maximum on kinetic curves shifts towards shorter residence times. Effective reaction rate constants were determined according to the suggested scheme of IDA synthesis. Calculated activation energies for two consecutive stages of IDA synthesis were found to be 73.7 and 67.2kJ/mol, respectively.