Reaction Rate Constant Research Articles

Reaction Rate Rules of Intramolecular H-Migration Reaction Class for RIORIIOO·Radicals in Ether Combustion.

The intramolecular H-migration reaction of RIORIIOO· radicals constitute a key class of reactions in the low-temperature combustion mechanism of ethers. Despite this, there is a dearth of direct computations regarding the potential energy surface and rate constants specific to ethers, especially when considering large molecular systems and intricate branched-chain structures. Furthermore, combustion kinetic models for large molecular ethers generally utilize rate constants derived from those of structurally similar alcohols or alkane fuels. Consequently, chemical kinetic studies involve the calculation of energy barriers and rate rules for the intramolecular H-migration reaction class of RIORIIOO· radicals, which are systematically conducted using the isodesmic reaction method (IRM). The geometries of the species participating in these reactions are optimized, and frequency calculations are executed using the M06-X method in tandem with the 6-31+G(d,p) basis set by the Gaussian 16 program. Moreover, the M06-2X/6-31+G(d,p) method acts as the low-level ab initio method, while the CBS-QB3 method is utilized as the high-level ab initio method for calculating single-point energies. Rate constants at the high-pressure-limit are computed based on the reaction class transition state theory (RC-TST) by ChemRate program, incorporating asymmetric Eckart tunneling corrections for intramolecular H-migration reactions across a temperature range of 500 to 2000 K. It was found that the isodesmic reaction method gives accurate energy barriers and rate constants, and the rate constants of the H-migration reaction for RIORIIOO· radicals diverge from those of comparable reactions in alkanes and alcohol fuels. There are significant disparities in energy barriers and rate constants across the entire reaction classes of the H-migration reaction for RIORIIOO· radicals, necessitating the subdivision of the H-migration reaction into subclasses. Rate rules are established by averaging the rate constants of representative reactions for each subclass, which is pivotal for the advancement of accurate low-temperature combustion reaction mechanisms for ethers.

Predicting thermochemical sulfate reduction reaction process and H2S generation in carbonate reservoirs using comprehensive kinetics modeling

Thermochemical sulfate reduction (TSR) is a critical process controlling hydrogen sulfide (H2S) generation in carbonate reservoirs, posing significant economic and safety challenges for the oil and gas industry. This study develops a comprehensive model that integrates detailed thermal, burial, and hydrocarbon generation histories with key TSR kinetic parameters, such as reaction rate constants and activation energies, to predict TSR evolution and H2S generation accurately. A notable feature of the model is to separate and quantify the contributions of different hydrocarbon species (CH4, C2-5, C6-14, and C15+) to the overall TSR process, using the Arrhenius equation to simulate the temperature-dependent behavior of TSR for each hydrocarbon group. The model also accounts for the in-reservoir thermal cracking of heavier hydrocarbons into light hydrocarbons, ensuring predictions closely align with geological processes. Modeling results show that TSR reactions accelerate the depletion of oil and wet gas components. A large amount of CH4 is generated due to both kerogen thermal cracking and alteration of heavy hydrocarbon. Our modeling also allows for accurate prediction of TSR reactions as well as the timing and extent of H2S and CO2 generation over the history of a reservoir. Applications in the Puguang and Hetianhe gas fields validate the model's broad applicability and reliability, capturing extensive TSR activities and being consistent with the observed data. These results underscore the models' robustness in detailed predictions of TSR dynamics across diverse geological settings and its potential as a valuable tool for managing sour gas production, aiding in risk assessment and resource management.

Degradation of tris(1,3-dichloro-2-propyl) phosphate (TDCPP) by ultraviolet activated hydrogen peroxide: Mechanisms, pathways and toxicity assessments

The ubiquity and ecotoxicity of tri (1,3-dichloro-2-propyl) phosphate (TDCPP) in aquatic environments make it essential to develop efficient related treatment techniques. The present research aims to systematically explore the mechanisms and toxicity changes of TDCPP degradation through UV-driven hydrogen peroxide process (UV/H2O2). The results revealed degradation efficiency of TDCPP attained 95 % with 0.5 mM H2O2, corresponding to a reaction rate constant (k) of 0.04919 min−1. Furthermore, three typical chlorinated OPEs (Cl-OPEs) were simultaneously degraded by the UV/H2O2 process, with different degradation efficiencies, according to the following order: TCEP<TDCPP<TCPP. The degradation efficiency was restricted under alkaline condition and the presence of humic acid (HA), nitrate (NO3–), chloride (Cl-), sulfate (SO42-), and dihydrogen phosphate (H2PO4-). A total of 12 intermediates were identified, which were generated through different pathways, including bond breaking, hydroxylation, and oxidation reactions. The Toxicity Estimation Software Tool (T.E.S.T) results demonstrated stronger mutagenicity and developmental toxicity of the TDCPP intermediates than parent compound. According to RNA sequencing results, UV/H2O2-based TDCPP degradation for 20 min and 60 min still had negative effects on Escherichia coli (E. coli). Indeed, the Gene Ontology (GO) enrichment and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis results further suggested the stronger negative effect (e.g., damaging effects on the cell membrane, energy metabolism, and vitality) of the 20-min oxidation solution on E. coli, followed by those observed in without treatment and 60-min oxidation solution. Therefore, longer oxidation times are required in the UV/H2O2 process to decrease the toxicity of TDCPP.

Mass Transfer Resistance and Reaction Rate Kinetics for Carbohydrate Digestion with Cell Wall Degradation by Cellulase.

This paper introduces an enzymatic approach to estimate internal mass-transfer resistances during food digestion studies. Cellulase has been used to degrade starch cell walls (where cellulose is a significant component) and reduce the internal mass-transfer resistance, so that the starch granules are released and hydrolysed by amylase, increasing the starch hydrolysis rates, as a technique for measuring the internal mass-transfer resistance of cell walls. The estimated internal mass-transfer resistances for granular starch hydrolysis in a beaker and stirrer system for simulating the food digestion range from 2.2 × 107 m-1 s at a stirrer speed of 100 rpm to 6.6 × 107 m-1 s at 200 rpm. The reaction rate constants for cellulase-treated starch are about three to eight times as great as those for starch powder. The beaker and stirrer system provides an in vitro model to quantitatively understand external mass-transfer resistance and compare mass-transfer and reaction rate kinetics in starch hydrolysis during food digestion. Particle size analysis indicates that starch cell wall degradation reduces starch granule adhesion (compared with soaked starch samples), though the primary particle sizes are similar, and increases the interfacial surface area, reducing internal mass-transfer resistance and overall mass-transfer resistance. Dimensional analysis (such as the Damköhler numbers, Da, 0.3-0.5) from this in vitro system shows that mass-transfer rates are greater than reaction rates. At the same time, SEM (scanning electron microscopy) images of starch particles indicate significant morphology changes due to the cell wall degradation.

Is Quantum Above-Barrier Reflection Important for Molecular Barrier Crossing Rates?

Understanding quantum tunneling and above-barrier reflection effects on unimolecular and bimolecular reaction rate constants remains challenging to this very day. In many applications, especially when considering moderate-to-high temperatures, the "standard" procedure is to use the parabolic barrier approximation. Recent work has shown though that this may be insufficient, and one cannot ignore anharmonicity. In this work, we study the analytic theory, including anharmonicity obtained when expanding the thermal rate up to order ℏ4. Such theories need high-order derivatives of the potential at the barrier top. We show that such derivatives are computed straightforwardly for six different reactions. We suggest a straightforward methodology for assessing whether the parabolic barrier approximation is valid and show that when the reaction asymmetry is large, this may lead to significant quantum above-barrier reflection and transmission coefficients, which are less than unity.

Evaporation-induced self-assembly Al doped black TiO2 for the degradation of tetracycline hydrochloride under visible light

Light absorption range, recycling stability and charge transfer efficiency are key to the performance of photocatalytic material. Based on these targets, a Al doped TiO2 catalyst was synthesized by the evaporation-induced process, after processed by NaBH4 reduction, the black TiO2 doped with Al was finally prepared. Uv-vis DRS, EPR and XPS analyses confirm the expanded light absorption window (300 nm - 1000 nm) and the introduction of abundant oxygen vacancy after the reduction process. The final product BTiO2/Al-0.5 has a degradation rate of about 84 % over the tetracycline hydrochloride within 60 minutes, the reaction rate constant (k) is 10.6 times higher than the unreduced sample. The dramatic change of photocatalytic ability can be assigned to the broadened visible light absorption, increased charge separation efficiency, narrowed band gap and defect-enriched oxygen vacancy. This work offers insights into the fabrication of TiO2 catalyst and the introduction of oxygen defect.

Quantitative and mechanistic elucidation of the reactive oxygen species for effective sulfamethoxazole removal in heterogeneous peroxymonosulfate activated by MOFs-derived cladding structure CoZn/NC@UiO

In cobalt-based catalyst/peroxymonosulfate (PMS) systems, the key issues are the leaching of metals and the stability of catalysts. In this study, a NH2-UiO-66 cladded CoZn/NC catalyst was synthesized for efficient degradation of sulfamethoxazole (SMX) using activated PMS. The removal efficiency of SMX could achieve 100% within 30 min. The leaching of Co2+ was inhibited to 0.05 ppm and the anti-interference and cyclic stability of the catalyst were enhanced by the NH2-UiO-66 shell. In addition, the quenching experiment, electron paramagnetic resonance (EPR) technique and probe experiment were used to analyze the reactive oxygen species (ROSs) qualitatively and quantitatively. The findings demonstrated that singlet oxygen (1O2) had the highest steady-state and cumulative concentration. However, 1O2 could only participate in the degradation of SMX through single electron transfer or addition reaction, resulting in a lower second-order rate constant of the SMX reaction with 1O2. Sulfate radical (SO4·-) contributed the most to the degradation of SMX due to the high reactivity of the sulfonamide structure in SMX to SO4·-. Finally, possible pathways for SMX degradation were proposed. The two primary mechanisms of SMX degradation were S-N cleavage and amino hydroxylation/oxidation. The toxicity of most of the intermediates was less than that of SMX through ecological structure–activity relationship analysis. Overall, a novel approach to synthesize low leaching and efficient cobalt based catalyst was put forward, and the activation mechanism of PMS was also revealed.

Hydration kinetics of C3A: effect of lithium, copper and sulfur-based mineralizers

AbstractCalcium aluminate phases have a particular effect on the early heat release during setting initiation and have a substantial influence on the further workability of ordinary Portland cement. The nature of the calcium aluminate hydration products and its kinetics strongly depends on sulfate content and humidity. The effect of mineralisers on melt formation and viscosity is well described for calcium silicate systems, but information is still lacking for calcium aluminates. Therefore, the synergistic effect on the crystal structure and hydration mechanism of the tricalcium aluminate phase of the addition of mineralizers, i.e. Li2O, CuO, SO3 to the raw meal is here investigated. Co-doped calcium aluminate structures were formed during high-temperature treatment. Thermal analysis (TG–DTA and heating microscopy) was used to describe the ongoing high-temperature reaction. Resulting phase composition was dependent on the concentration of the mineralizer. While phase pure system was prepared with low mineralizer concentrations, with increasing mineralizer content the secondary phases were formed. Raman spectroscopy and XPS analysis were used to investigate the cation substitution and to help describe the cations bonding in co-doped calcium aluminate system. Prepared powders have been hydrated in a controlled manner at different temperatures (288, 298, 308 K). The resulting calorimetric data have been used to investigate the hydration kinetics and determine the rate constant of hydration reaction. First-order reaction (FOR) model was here applied for the activation energy and frequency factor calculations. The metastable and stable calcium aluminate hydrates were formed according to initial phase composition. In phase pure systems with low S content, the formation of stable and metastable hydrates was depended on the reaction temperature. Conversely, in systems with secondary phases and higher S content, the hydration mechanism resembled that which appears in calcium sulfoaluminates.

Ortho to para hydrogen conversion over bimetallic iron and cobalt catalysts

The catalytic conversion of ortho-hydrogen (o-H2) to para-hydrogen (p-H2) serves as a crucial step in the storage of liquid hydrogen. A variety of iron-cobalt bimetallic catalysts (FCO) were synthesized using a precipitation method, incorporating diverse levels of Co doping into Fe-based catalysts. The effects of Co doping on the crystal structure, porosity, and magnetism of FCO catalysts were studied by XRD, N2 physical adsorption, FTIR, XPS, and VSM analyses. The efficiency of ortho-para hydrogen conversion over FCO at 77 K was evaluated. It was found that the catalyst’s lag coefficient was significantly improved by Co doping, leading to an increase of magnetic moment. The catalyst of FCO-5 with a Fe/(Fe + Co) molar ratio of 0.5 exhibited the highest activity in ortho-para hydrogen conversion. The corresponding conversion rate, outlet p-H2 content, and the reaction rate constant were 99.2%, 49.7% and 291.7 mol·L−1·s−1, respectively, under a gas hourly space velocity of 5400 h−1.

Kinetics of Thermal Decomposition of N-Propargil Derivatives of 7&lt;i&gt;H&lt;/i&gt;-Difurazanofuxanoazepine and 7&lt;i&gt;H&lt;/i&gt;-Trifurasanoazepine

The thermal stability of the propargyl derivatives of 7H-difurazanofuroxanoazepine and 7H-trifurazanoazepine in isothermal and non-isothermal modes has been studied. Formal kinetic regularities of decomposition and temperature dependences of reaction rate constants are determined. The thermal stability of propargyl, cyanomethyl, allyl and amine derivatives of azepines is compared.

H-atom abstraction reactions of C1-C4 alkanes by ketenyl radical: Kinetic investigation and analysis

The kinetics of 16 H-atom abstraction reactions of C1-C4 alkanes by ketenyl radical (HCCO) are studied to enhance the existing combustion mechanisms. Firstly, the obtain the lowest-energy conformer, vibration frequencies and single point energies for the reactants, prepolymers, transition states, and products are determined using the CCSD(T)/cc-pVQZ//B3LYP/6-311G+(d,p) theory level. Subsequently, temperature-dependent reaction rate constants for the major channels are predicted by the TST method. Finally, the H-atom abstraction reactions are validated under multiple temperature conditions, and the effects of the reactions on auto-ignition process and CO emission characteristics of n-heptane/NG mixture are researched. The results indicate that the H-atom abstraction reactions by Cα-atom play a significant role for the diesel/NG combustion. To combine the reaction pathways and rate constants into the existing kinetic mechanisms resulted in more accurate predictions of the ignition delay time. Furthermore, these kinetics data are valuable for revealing the CO emissions of the dual-fuel engines.

Insight into the Kinetics of Isomerization and β-Scission Reactions Following H-Abstraction in 2-Pentanone Combustion.

2-Pentanone is a significant carbon-neutral fuel. To better understand 2-pentanone combustion, the CCSD(T)/CBS method was used to calculate the potential energy surfaces (PES) for H-abstraction, isomerization, and β-scission reactions of 2-pentanone. Rate constants for the above reactions were calculated by the MESS employing conventional transition state theory (CTST) at 300-2000 K. The findings reveal adherence to the Evans-Polanyi principle in the H-abstraction reactions of 2-pentanone by H atoms. Specifically, the 2-site shows more competitive kinetics due to having the lowest energy barrier of 7.8 kcal/mol. The 4-position has the highest energy barrier, making the reaction difficult to occur. In the subsequent reactions, the breaking of C-H bonds is most competitive at low temperatures. In particular, the H transfer from INT1 to INT3 has a potential well height of 24.8 kcal/mol. The β-scission reactions become the main pathway for the depletion of pentanone radicals with increasing temperature. This study significantly extends the kinetic parameters of 2-pentanone combustion over a wide range of temperatures and pressures, which is expected to contribute to the development of 2-pentanone combustion models.

Kinetic insights into double-branched acyclic ether: Methyl tert-butyl ether and 2,2-dimethoxypropane

This study presents the first kinetic mechanism for methyl tert-butyl ether (MTBE) containing low-temperature chemistry, as well as the first mechanism for 2,2-dimethoxypropane (DMP). The mechanisms have been validated against ignition delay time experiments conducted in a high-pressure shock tube and rapid compression machine. The rapid compression machine conditions were set to 20 and 40 bar for MTBE, and 10 and 20 bar for DMP in a temperature range of 584 to 946 K. Shock tube experiments have been performed for DMP at 20 and 40 bar for stoichiometric and fuel-lean conditions in air at temperatures ranging from 913 to 1173 K. A pronounced negative temperature coefficient regime with two-stage ignition has been observed for both fuels. The developed mechanism consists of reaction rate constants that were primarily modeled in analogy to iso-octane and dimethoxymethane, and calculated thermodata on the G4//B3LYP-D3BJ/def2-TZVP level of theory. Simulations have been performed to analyze the fuel oxidation at different temperatures. Over the full temperature range, H-atom abstraction occurs mainly on the α-side for DMP and on the β-side for MTBE. At low temperatures, both fuels isomerize to the peroxy radical. The dominant MTBE radicals then tend to produce cyclic ether, while the DMP radicals react with O2, enabling significant chain branching and explaining the higher reactivity of DMP. With rising temperature, β-scission of the fuel radicals and unimolecular elimination reactions start to dominate the oxidation process.Novelty and Significance StatementThe novelty of this research is the first observation of a two-stage ignition of methyl-tert butyl ether (MTBE) in an RCM and a discussion of its fundamental ignition chemistry, which is based on a developed detailed kinetic mechanism. In addition, 2,2-dimethoxypropane (DMP) has been investigated experimentally and theoretically to explain the difference in reactivity to MTBE despite their strong molecular similarity. The experiments include RCM and shock tube experiments. The kinetic model is based on rate constant analogies and newly calculated thermo data on the G4//B3LYP-D3BJ/def2-TZVP level of theory. This work is significant, as MTBE is still a widely used octane booster and the developed model could help to improve engine simulations. Furthermore, the findings of DMP provide insights into future fuel design.

DEVELOPMENT OF AN ALGORITHM FOR CALCULATING THE RATE CONSTANT OF HYDROCHLORIC ACID REACTION WITH A CARBONATE ROCK FORMATION

One of the main factors reducing acid stimulation efficiency is the intensive reaction of active acid in the immediate vicinity of the wellbore, which leads to insufficient completeness of reservoir rock dissolution in the remote reservoir zone. The reservoir hydrodynamic characteristics are not being improved properly, and the efficiency of oil production stimulation measures does not reach the planned values.To get high results of acid treatments it is necessary to achieve deep penetration of acid into the formation thickness. The reaction rate constant is used to compare the reactivity of different acid compositions and to select the most suitable acid composition for the geological and physical conditions of the treated object, which provides the highest treatment efficiency. It relates the initial substances concentrations with reaction products formation rate. To determine the reaction rate constant, a volumetric apparatus was created and methodological aspects were developed to work on it, allowing to minimize the measurement error and to achieve the greatest accuracy in determining the kinetic parameters of the reaction. But in the course of further investigations in the work of the existing algorithm for experimental data processing, a number of significant deficiencies distorting the results of calculations were revealed. The aim of the research is to develop a new improved algorithm for reaction rate constant calculation, which will improve the understanding of the process of determining the kinetic parameters of acid reaction with carbonate rock.To achieve this aim, the authors conducted a series of experiments according to the unified methodology, the results of which revealed ways to eliminate the identified deficiencies using a new algorithm. It includes obtaining and saving initial data, subsequent treatment and direct calculation of reaction kinetic parameters with results saving.The developed algorithm makes it possible to unify and automate the process of determining the kinetic parameters of the acid reaction with the formation rock, as well as to determine the reaction characteristics with higher accuracy and reduce the influence of the human factor on the research results, thus reducing the errors of the calculation results.

Preparation of Fe-doped coffee ground biochar and activation of PMS for chloroquine phosphate removal

Iron-doped biochar catalyst (Fe-CGB) was synthesized by embedding rust into coffee grounds using a high-temperature water bath. Fe-CGB was then used with activated peroxymonosulfate (PMS) to treat chloroquine phosphate (CQP) contaminated wastewater. The presence of biochar facilitates the cycling between Fe(III) and Fe(II) species, thereby augmenting the activation efficacy of PMS. The Fe-CGB/PMS system demonstrated exceptional catalytic degradation efficacy, achieving complete removal of CQP within a mere 30 min, with a reaction rate constant of 0.1501 min−1, surpassing the unmodified coffee grounds biochar by a factor of 47. Notably, under extreme pH conditions and in the presence of complex inorganic ions, CQP was entirely eliminated within 60 min. Mechanistic investigations revealed that biochar-mediated promotion of the Fe(III)/Fe(II) cycle amplifies the activation efficiency of PMS, leading to the generation of abundant sulfate radicals (SO4·−) and hydroxyl radicals (·OH), which facilitate pollutant decomposition. Furthermore, Fe-CGB exhibited notable stability across multiple cycles, with minimal iron ion leaching and facile separation from the solution. Subsequently, the degradation effects of 18 organic pollutants were evaluated, and their potential as effective treatment methods for multiple pollution scenarios were explored in combination with theoretical calculations. Overall,this study provides insights into PMS activation as well as waste management.

Framework Integrated with Flow Cell Experiments and Simulations for Understanding Etching in Chemical Conversion Treatments

In this study, a new framework integrates simulations and flow cell experimentation to quantitatively understand the mechanism of chemical treatment reactions. Using this framework, the mechanisms of etching reactions induced by weak and strong acids were specifically investigated. A flow cell system experiment was developed for the etching experiment. Two acids (HNO3 and HF) were used, along with HNO3 without electrolytes. Average flow velocities were measured, and the molar flux of Fe2+ ions was determined by sampling the solution passing through the flow cell and measuring the iron content by using inductively coupled plasma. A concentration field simulation of the etching reaction in the flow cell was conducted. The concentration field within the boundary layer was visualized to understand the mechanism of H+ ion supply to the metal surface. In the case of weak acid solutions, H+ ions are primarily supplied by dissociation. In contrast, they were supplied by diffusion in strong acid solutions. A boundary layer formed within 100 μm from the metal surface. The experimental and simulated molar flux of Fe2+ ions were compared. The molar flux attributed to weak acid etching was more than 10 times that attributed to strong acids. The reaction rate constant of the H+ reduction reaction was evaluated through a parameter study. The influence of spectator ions on the etching process was investigated. An experiment was conducted to compare the etching of iron plates using HNO3 solutions with different concentrations of spectator ion. The results confirmed that the higher the concentration of the spectator ion, the greater the etching amount. Numerical analysis revealed that the electric field in the electric migration term acts in a direction that impedes the movement of H+ ions to the metal surface. While it is already known that electric migration inhibits electrode reactions, this study enabled its quantitative visualization and evaluation.

Regulating oxidation states of Cu nanowires for enhanced catalytic reduction of 4-nitrophenol

Abstract The construction of highly efficient and low-cost catalysts is crucial for the reduction reaction of 4-nitrophenol (4-NP). Herein, we provide a simple processing method, including vacuum storage, natural oxidation, and heating oxidation, that effectively regulates the surface oxidation state of copper nanowires and produces copper nanowires with different oxidation states (such as Cu, Cu2O, and CuO). Research has found that CuNW-N (Cu nanowires for vacuum storage) catalysts with a surface composition of 67.9% Cu0, 20.6% Cu+, and 11.5% Cu2+ exhibit the best catalytic performance for the reduction of 4-nitrophenol (4-NP) and their reaction rate constant reaches 0.791 min−1. This work provides a feasible catalyst preparation strategy for the efficient catalytic reduction of 4-NP.

Structural and functional analysis of a bile salt hydrolase from the bison microbiome

The bile salt hydrolases (BSHs) are significant constituents of animal microbiomes. An evolving appreciation of their roles in health and disease has established them as targets of pharmacological inhibition. These bacterial enzymes belong to the N-terminal nucleophile superfamily and are best known to catalyze the deconjugation of glycine or taurine from bile salts to release bile acid substrates for transformation and or metabolism in the gastrointestinal tract. Here, we identify and describe the BSH from a common member of the Plains bison microbiome, Arthrobacter citreus (BSHAc). Steady-state kinetic analyses demonstrated that BSHAc is a broad-spectrum hydrolase with a preference for glycine-conjugates and deoxycholic acid (DCA). Second-order rate constants (kcat/KM) for BSHAc-catalyzed reactions of relevant bile salts-glyco- and tauro-conjugates of cholic acid and DCA- varied by ∼30-fold and measured between 1.4× 105 and 4.3× 106M-1s-1. Interestingly, a pan-BSH inhibitor named AAA-10 acted as a slow irreversible inhibitor of BSHAc with a rate of inactivation (kinact)of ∼2h-1 and a second order rate constant (kinact/KI) of ∼24M-1s-1 for the process. Structural characterization of BSHAc reacted with AAA-10 showed covalent modification of the N-terminal cysteine nucleophile, providing molecular details for an enzyme-stabilized product formed from this mechanism-based inhibitor's α-fluoromethyl ketone warhead. Structural comparison of the BSHs and BSH:inhibitor complexes highlighted the plasticity of the steroid-binding site, including a flexible loop that is variable across well-studied BSHs.

Construction of ZnCo2O4/Ag3PO4 composite photocatalyst for enhanced photocatalytic performance

AbstractIn this study, ZnCo2O4/Ag3PO4 composite catalyst was prepared by the precipitation method, and their performance in the photocatalytic degradation of methyl orange (MO) was studied. The catalysts were characterized by scanning electron microscopy, high‐resolution transmission electron microscopy, X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, selected area electron diffraction, X‐ray photoelectron spectroscopy, and UV‐Vis diffuse reflectance spectroscopy. The results indicate that the 0.1 ZnCo2O4/Ag3PO4 composite system has good photocatalytic activity in the degradation of methyl orange. Under simulated sunlight conditions, the degradation rate can reach 94% after 30 min. The maximum reaction rate constant of 0.1 ZnCo2O4/Ag3PO4 was 0.05301 min−1, which is 3 times and 52 times the rate constant of pure Ag3PO4 and pure ZnCo2O4, respectively. In catalyst recycling experiments, 0.1 ZnCo2O4/Ag3PO4 still degraded methyl orange at a rate of 84.4% after three cycles. Trapping experiments showed that holes and superoxide radicals mostly contributed to the photocatalytic degradation of methyl orange by the catalyst, while hydroxyl radicals played a partial role. The energy level structure of ZnCo2O4/Ag3PO4 is conducive to the effective separation of photogenerated electrons and holes, improving the lifespan of photogenerated charges. In the investigated catalyst series, 0.1 ZnCo2O4/Ag3PO4 demonstrated the best photocatalytic performance.

Modifying the second coordination spheres of Fe active sites for electrocatalytic nitric oxide reduction in realistic electrochemical environment

The first and second coordination spheres in the coordination microenvironment may regulate the electronic structure of single-metal atoms supported on carbon matrix, which in turn modulates the catalyst’s catalytic activity. Simulating the kinetic process of electrocatalytic nitric oxide reduction reaction (NORR) by the theoretical modeling of electrochemical microenvironments helps understand the theoretical structure–activity relationship and guides a more rational design of electrocatalysts. In this study, density functional theory calculations combined with a constant-potential/hybrid-solvent model and microkinetic modeling are employed to study NORR mechanism on the carbon-based FeN4, FeN4-O and FeN4-B catalysts with different electronegativity atoms in the second coordination spheres under −1.00 ∼ 0.40 V vs. RHE. The free energy changes of all elementary reactions for NORR on the catalysts reveal that the optimal pathways for NORR on FeN4 produce both ammonia and hydroxylamine, proceeding through the reaction intermediates *NHOH. Within −1.00 ∼ -0.37 V vs. RHE, the kinetic barriers of the rate-determining steps for NORR increase sequentially on FeN4, FeN4-O, and FeN4-B, corresponding to the sequentially decreasing reaction rate constants. At −6.00 mA∙cm−2, the electrode potential for ammonia production on FeN4 catalyst is the lowest among the catalysts at −0.70 V vs. RHE, indicating it has higher electrocatalytic activity.