Multistep Mechanism Research Articles

Unlocking power of neighboring vacancies in boosting hydrogen evolution reactions on two-dimensional NiPS3 monolayer

This study investigates the effect of defect engineering on the catalytic activity of a NiPS3 monolayer catalyst for the hydrogen evolution reaction (HER). Three different types of vacancies on the basal plane of the monolayer are explored through a multi-step mechanism involving the dissociative adsorption of a water molecule and subsequent electrochemical adsorption of the dissociated proton. Co-formation of vacancies in both Ni and S sites is found to be the most effective in enhancing the catalytic performance of the monolayer. A key resource for the reaction thermodynamics is the S-substitution-like physisorption of a water molecule on a vacant S site, followed by the dissociative occupation of OH and H into vacant sites of S and Ni elements, boosted by the NiS di-vacancy configuration with low activation energy barriers. Investigation reveals the highest contribution of bonding orbitals to the monolayer-H bond makes it the most desirable defect engineering approach for transition metal phosphorus chalcogenides with high HER activities. Overall, this study highlights the significance of controlled defect engineering in augmenting the catalytic performance of NiPS3 monolayer catalysts for HER.

Aqueous Radical Initiated Oxidation of an Organic Monolayer at the Air-Water Interface as a Proxy for Thin Films on Atmospheric Aerosol Studied with Neutron Reflectometry.

Neutron reflectometry has been used to study the radical initiated oxidation of a monolayer of the lipid 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) at the air-solution interface by aqueous-phase hydroxyl, sulfate, and nitrate radicals. The oxidation of organic films at the surface of atmospheric aqueous aerosols can influence the optical properties of the aerosol and consequently can impact Earth's radiative balance and contribute to modern climate change. The amount of material at the air-solution interface was found to decrease on exposure to aqueous-phase radicals which was consistent with a multistep degradation mechanism, i.e., the products of reaction of the DSPC film with aqueous radicals were also surface active. The multistep degradation mechanism suggests that lipid molecules in the thin film degrade to form progressively shorter chain surface active products and several reactive steps are required to remove the film from the air-solution interface. Bimolecular rate constants for oxidation via the aqueous phase OH radical cluster around 1010 dm3 mol-1 s-1. Calculations to determine the film lifetime indicate that it will take ∼4-5 days for the film to degrade to 50% of its initial amount in the atmosphere, and therefore attack by aqueous radicals on organic films could be atmospherically important relative to typical atmospheric aerosol lifetimes.

Molecular View on the iRGD Peptide Binding Mechanism: Implications for Integrin Activity and Selectivity Profiles.

Receptor-selective peptides are widely used as smart carriers for specific tumor-targeted delivery. A remarkable example is the cyclic nonapeptide iRGD (CRGDKPGDC, 1) that couples intrinsic cytotoxic effects with striking tumor-homing properties. These peculiar features are based on a rather complex multistep mechanism of action, where the primary event is the recognition of RGD integrins. Despite the high number of preclinical studies and the recent success of a phase I trial for the treatment of pancreatic ductal adenocarcinoma (PDAC), there is little information available about the iRGD three-dimensional (3D) structure and integrin binding properties. Here, we re-evaluate the peptide's affinity for cancer-related integrins including not only the previously known targets αvβ3 and αvβ5 but also the αvβ6 isoform, which is known to drive cell growth, migration, and invasion in many malignancies including PDAC. Furthermore, we use parallel tempering in the well-tempered ensemble (PT-WTE) metadynamics simulations to characterize the in-solution conformation of iRGD and extensive molecular dynamics calculations to fully investigate its binding mechanism to integrin partners. Finally, we provide clues for fine-tuning the peptide's potency and selectivity profile, which, in turn, may further improve its tumor-homing properties.

DFT Study of the SNAr Reactions of 1‐Chloro‐2‐nitro‐ and 1‐Phenoxy‐2‐nitro‐benzenes with Aniline in Acetonitrile and Toluene: Concerted or Multistep Mechanism?

AbstractComputational studies to determine the rate constants and thermodynamic properties of the nucleophilic aromatic substitution reactions of 4‐R‐1‐chloro‐2,6‐dinitrobenzenes 1, 6‐R‐1‐chloro‐2,4‐dinitrobenzenes 2 and some of the corresponding 1‐phenoxy derivatives 3 and 4 with aniline in the gas phase, acetonitrile and toluene is reported at the M06‐2x/6‐31g+(d,p) level of theory; R=H, NO2, CF3, CN and ring N. Formation of the Meisenheimer complex intermediate was observed in all cases and its stability was dependent on the number of electron‐withdrawing groups present on the ring and their relative position. The overall reaction was found to be exothermic and exergonic in all cases. From kinetics calculations, the initial attack of the aniline nucleophile on the dinitrobenzene to form the intermediate is rate limiting with the chloride ion as the leaving group in acetonitrile and decomposition of the MC was rate limiting in vacuum and toluene. With the phenoxide ion as the leaving group, the decomposition of the MC intermediate is rate limiting in all cases. The observation of MC and thermodynamic data obtained are suggestive of the prevalence of a multistep SNAr mechanism and ring activation by electron withdrawing group increased the rate of reaction.

Ab Initio Study of Glycine Formation in the Condensed Phase: Carbon Monoxide, Formaldimine, and Water Are Enough

Glycine is considered to be crucial in the formation of proteins and prebiotic substances. Nevertheless, the mechanism of spontaneous glycine formation under prebiotic Earth conditions or within the interstellar medium (ISM) remains a topic of debate, given the changing geochemical environment over Earth’s history and the difficulty of detecting it within the ISM. Yet it is believed that its formation could be possible in interstellar water-rich ice. In this study, using molecular dynamics (MD) simulations at the ab initio level of theory enhanced with modern free energy calculations, we modeled the chemical reaction between carbon monoxide, formaldimine, and water to produce glycine. We estimated under what conditions, in condensed phase at 50, 70, 100, and 300 K, glycine is formed. We also explored the effect of different electric fields on this process. Our results show that glycine could be formed with energy barriers as low as 0.5 kcal mol−1 at 50 K. We discuss whether this reaction could be a suitable candidate for explaining the mechanism of glycine formation under conditions that resemble various astrophysical environments, such as planets, exoplanets, and Earth. This study is relevant to finding a consensus among various proposals for glycine formation. Moreover, it highlights the importance of metadynamics and Car–Parrinello MD methods as tools in finding unknown complex, multistep reaction mechanism pathways, possibly important to the astronomical phenomena.

High-speed AFM imaging reveals DNA capture and loop extrusion dynamics by cohesin-NIPBL

3D chromatin organization plays a critical role in regulating gene expression, DNA replication, recombination, and repair. While initially discovered for its role in sister chromatid cohesion, emerging evidence suggests that the cohesin complex (SMC1, SMC3, RAD21, and SA1/SA2), facilitated by NIPBL, mediates topologically associating domains and chromatin loops through DNA loop extrusion. However, information on how conformational changes of cohesin-NIPBL drive its loading onto DNA, initiation, and growth of DNA loops is still lacking. In this study, high-speed atomic force microscopy imaging reveals that cohesin-NIPBL captures DNA through arm extension, assisted by feet (shorter protrusions), and followed by transfer of DNA to its lower compartment (SMC heads, RAD21, SA1, and NIPBL). While binding at the lower compartment, arm extension leads to the capture of a second DNA segment and the initiation of a DNA loop that is independent of ATP hydrolysis. The feet are likely contributed by the C-terminal domains of SA1 and NIPBL and can transiently bind to DNA to facilitate the loading of the cohesin complex onto DNA. Furthermore, high-speed atomic force microscopy imaging reveals distinct forward and reverse DNA loop extrusion steps by cohesin-NIPBL. These results advance our understanding of cohesin by establishing direct experimental evidence for a multistep DNA-binding mechanism mediated by dynamic protein conformational changes.

Crystallization kinetics of Sb70Se30 thin films for phase change memories under the non-isothermal conditions

We investigate the non-isothermal crystallization kinetics of Sb70Se30 thin films using differential scanning calorimetry and determine the kinetic triplet of Sb70Se30 thin films at various heating rates by combining model-free and model-fitting approaches. The results indicate that the crystallization activation energy decreases with increasing crystallization fraction α, confirming the presence of multi-step crystallization mechanism. In accordance with the local Avrami index n(α), the crystallization mechanism shifts from three-dimensional growth with an increased nucleation rate at 0.05 ≤ α ≤ 0.8 to three- and two-dimensional growth with a reduced nucleation rate at α＞0.8. Afterwards, we deduce that the Sb70Se30 thin films follow a second-order reaction model within the heating rate range of 20 to 40 K/min. Moreover, the Sb70Se30 thin film shows excellent data retention capability when predicting data processing and data storage time based on phase change memory units. These findings provide valuable insights into the crystallization kinetics of Sb70Se30 thin films, contributing to the advancement of phase change materials.

Preparation and Use of Iron on Carbon Foam for Removal of Organic Dye from Water: Batch Studies.

The presence of dyes in effluents from textile industries has a detrimental effect on aquatic ecosystems as it hinders the process of photosynthesis by reducing the penetration of sunlight. The adsorption capacity of a carbon foam-based iron oxide sorbent obtained from natural sources for the removal of organic methylene blue (MB) dye from water was investigated. The adsorption capacities were examined by batch experiments, wherein the impacts of varying iron content, sorbent dosage, contact time, dye concentration, and characterization were assessed. The physical characteristics and surface morphology of the synthesized carbon foam were also investigated. The carbon precursor and iron oxide precursor were coalesced within a singular container and subjected to carbonization process. This resulted in the formation of a porous structure that is capable of effectively providing support to the iron oxide particles. The carbon foam produced is a self-assembled formation that possesses the characteristic shape and underlying network structure reminiscent of bread. As the number of nanoparticles went up, so did the number of active sites. At elevated temperatures, the interactions between the dye molecules were enhanced, resulting in a more efficient process of dye removal. The magnetite sample exhibited endothermic adsorption, and all other samples exhibited exothermic adsorption. The adsorption of MB onto iron supported by carbon foam did not exhibit intraparticle diffusion as the only rate-limiting step for all samples. The adsorption rate was governed by a multistep elementary reaction mechanism in which multiple processes occurred simultaneously. The experimental data in this study may be accurately modeled by the pseudo-second-order kinetic model (R2 > 0.96). Additionally, the Freundlich isotherm best describes the adsorption equilibrium, which is supported by the outstanding fit of data to the model (R2 > 0.999). The findings suggest that the utilization of a natural carbon foam as a support for an immobilized iron oxide sorbent demonstrates considerable effectiveness in the removal of methylene dye from industrial effluent.

Simulation of co-pyrolysis of coffee ground and waste polystyrene foam in a tilted-slide reactor

Coffee ground is considered one of the promising biomass resources because it is one of the most popular beverages and has higher calorific value than other kinds of biomass. In the previous study on the fast pyrolysis of coffee ground, the viscosity of the pyrolysis oil was found to be very high and it was suggested to mix some amount of alcohol to reduce its viscosity. The quality of the pyrolysis oil also can be improved by mixing synthesis polymer such as polyethylene, polyethylene, or polystyrene as a feedstock. Recently, a tilted-slide reactor for fast pyrolysis was designed with a feeding capacity of 20 kg/h, in which no fluidizing gas is necessary for conveying hot sand. In the previous experiment, the co-pyrolysis of coffee ground and waste polystyrene foam was performed in the tilted-slide reactor. The ratio of waste polystyrene foam in the feedstock mixture was varied from 0% to 100% by weight, and fast pyrolysis was performed near the temperature of 550 °C. In this study, the co-pyrolysis was simulated by a commercial computational fluid dynamics code, and the results were compared with experimental results. A multistep kinetic mechanism was adopted for the pyrolysis of coffee ground and polystyrene. The volatile yields in the simulation approached the pyrolysis oil yields in the experiment by introducing a composite boundary condition to retain the unpyrolyzed polystyrene near the reactor bottom for longer residence time. The elemental composition and moisture contents became similar with measurement when increasing polystyrene blending ratio.

Competitive adsorption of VOCs (benzene, xylene and ethylbenzene) with Fe3O4@SiO2-NH@BENZOPHENONE magnetic nanoadsorbents

Volatile organic compounds (VOCs), which are toxic, mutagenic and carcinogenic, are considered a critical factor for air pollution and cause serious harm to the eco-environment and human health. In this study, Fe3O4, Fe3O4@SiO2-NH2, Fe3O4@SiO2-NH@BENZOFENONE were synthesized as new magnetic nanoadsorbents (MNAs) and used for the first time in the removal of gas-phase benzene, xylene and ethylbenzene. The synthesised MNAs were characterized by SEM-EDS, TEM, FTIR, XRD, VSM, TGA and BET analyses. The characterization results showed that the MNAs have mesoporous structure, type IV physioresorption and type H3 hysteresis loop character. In order to clarify the comparative and competitive adsorption behaviour, the adsorption capacity of Fe3O4@SiO2-NH@BENZOFENONE MNA was found to be in the order of xylene > ethylbenzene > benzene in both single, binary and ternary component systems. The adsorption kinetics of benzene, xylene and ethylbenzene with Fe3O4@SiO2-NH@BENZOFENONE MNA were found to be governed by multistep mechanisms. Fe3O4@SiO2-NH@BENZOFENONE MNA showed reuse efficiencies of 83.07%, 84.35% and 82.99% after 5 cycles for benzene, xylene and ethylbenzene respectively. In the framework of the results, Fe3O4@SiO2-NH@BENZOPHENONE MNA, which has a high potential in terms of both adsorption capacity and reuse efficiency, is proposed as a promising adsorbent for the efficient removal of benzene, xylene and ethylbenzene.

Architecture of the MKK6-p38α complex defines the basis of MAPK specificity and activation.

The mitogen-activated protein kinase (MAPK) p38α is a central component of signaling in inflammation and the immune response and is, therefore, an important drug target. Little is known about the molecular mechanism of its activation by double phosphorylation from MAPK kinases (MAP2Ks), because of the challenge of trapping a transient and dynamic heterokinase complex. We applied a multidisciplinary approach to generate a structural model of p38α in complex with its MAP2K, MKK6, and to understand the activation mechanism. Integrating cryo-electron microscopy with molecular dynamics simulations, hydrogen-deuterium exchange mass spectrometry, and experiments in cells, we demonstrate a dynamic, multistep phosphorylation mechanism, identify catalytically relevant interactions, and show that MAP2K-disordered amino termini determine pathway specificity. Our work captures a fundamental step of cell signaling: a kinase phosphorylating its downstream target kinase.

Recent Advances in CoSex and CoTex Anodes for Alkali-ion Batteries

Transition metal selenides have narrow or zero band-gap characteristics and high theoretical specific capacity. Among them, cobalt selenide and cobalt telluride have some typical problems such as large volume changes, low conductivity, and poor structural stability, but they have become a research hotspot in the field of energy storage and conversion because of their high capacity and high designability. Some of the innovative synthesis, doping, and nanostructure design strategies for CoSex and CoTex, such as CoSe-InCo-InSe bimetallic bi-heterogeneous interfaces, CoTe anchoring MXenes, etc., show great promise. In this paper, the research progress on the multistep transformation mechanisms of CoSex and CoTex is summarized, along with advanced structural design and modification methods such as defect engineering and compositing with MXenes. It is hoped that this review will provide a glimpse into the development of CoSex and CoTex anodes for alkali-ion batteries.

Asymmetric reductive carboxylation of N-(2-bromophenyl)-N-methylmethacrylamide with CO2 catalyzed by nickel complex: A theoretical study

To provide guiding information for developing efficient catalysts for CO2 carboxylation, we investigated the mechanism of asymmetric reductive carboxylation of N-(2-bromophenyl)-N-methylmethacrylamide with CO2 catalyzed by a nickel complex using density functional theory (DFT) calculations. The reaction was found to proceed via a multistep and elaborate mechanism. Additionally, CO2 exhibits a preference for inserting into the Ni(I) intermediate rather than Ni(II) intermediate. The noncovalent interaction (NCI) analysis reveals that the π-π stacking interactions and hydrogen bonding interactions lead to the stereoselectivity.

Screening for tolerance to natural phenols of different algal species: Toward the phycoremediation of olive mill wastewater

Olive Mill Wastewater (OMWW) is a by-product of olive oil production and it is rich in nutrients (e.g. P, N and K) and phenolic compounds. These latter are aromatic compounds, and their concentrations can reach up to 11 g L−1 in OMWW. A complete remediation of OMWW is required since phenols are known to cause toxicity once released in the environment: particularly, their effect on microorganisms is species-specific and primarily depends on the chemical structure of the compound. Microalgae have already been tested to remediate OMWW, data are promising but how different phenols affect algal growth is still poorly known. In this work, ten microalgal species belonging to different phylogenetic groups and natural habitats, were grown in the presence of three phenolic compounds found in OMWW (tyrosol, coumaric acid, caffeic acid). Algal growth and removal of phenolic compounds were assessed. Tyrosol was the only compound allowing growth of each tested microalga similarly to what observed in control media. Growth of microalgae and removal of phenolic compounds were not always related, and a multi-step phenolic removal mechanism was suggested. Species such as Nannochloropsis salina and Porphyridium purpureum rapidly died after the addition of coumaric acid or caffeic acid but a high removal percentage (60–100 %) of the phenols was still observed and it was likely due to their absorbance onto the cell surface. On average, freshwater species showed a higher growth performance compared to the one of marine species; in particular, Tetradesmus obliquus and Anabaena sp. showed the best results. This work elucidates a species-specific effect for each phenolic compound on algal growth and it also highlights that growth and removal are not related phenomena.

Flame Surface Density and Artificially Thickened Flame Combustion Models Applied to a Turbulent Partially-Premixed Flame

The Sydney Flame provides an excellent framework for systematic analysis of premixed, partially premixed and non-premixed methane/air combustion. It represents (depending on the axial position from the fuel inlet) non-premixed, partially premixed and fully premixed combustion. We simulate the test case FJ200-5GP-Lr75-57, which represents the partially premixed mode. Large-eddy simulations (LES) are conducted using a flame surface density combustion model (FSD) using one-step chemistry and an artificially thickened flame model (ATF) with a global two-step and an analytically reduced multi-step chemistry reaction mechanism. Unity Lewis numbers are assumed (Le=1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$Le=1$$\\end{document}) at first. The FSD and ATF models are compared using the same computational mesh, numerical scheme and boundary conditions. Both models will be analysed regarding their accuracy and computational efficiency in the regime of partially premixed combustion. A comparison of the results points out the strengths and weaknesses of the FSD models. The FSD model with inclusion of flame stretch effects yields good agreement with mean experimental temperature, CO2 and H2O mass fraction distributions in contrast to the ATF model using the global two-step mechanism, which overestimates downstream temperature, CO2 and H2O mass fractions. The FSD model performs well in all regions, which are dominated first by premixed, then partially premixed and finally non-premixed combustion along the flame. The ATF multi-step chemistry shows good results only in the premixed mode region, while mean temperature, CO2 and mass fractions are overestimated in the non-premixed mode regions at higher mixture fraction values. Including differential diffusion into the transport equations improved the ATF model results in comparison with experiments. A mesh study revealed, that the ATF model performs only after mesh refinement. In particular results are improved in the non-premixed combustion region. In contrast, the FSD model is less resolution sensitive and performs very well for both meshes. An evaluation of the Wasserstein metric provides a quantitative assessment of different ATF model setups on simulation accuracy. Finally, computational times for all simulation setups are compared.

Mechanism, Kinetics and Simulation of Electrocatalytic Oxidation of Dimethylamine Borane (DMAB) on Electroless Gold

Dimethylamine borane ((CH3)2NHBH3) or DMAB, is broadly used as a reducing agent in electroless autocatalytic platings like gold and nickel-boron, hydrogen storage, and reductive amination. However, the mechanism of its DMAB oxidation procedure remains unclear. This project is based on the hypothesis that a multi-step electron transfer mechanism exists for oxidizing the reducing agent DMAB on gold in alkaline media. According to this mechanism, the active species produced when DMAB is used at high hydroxide content is the BH3OH-. This species is created through a series of irreversible electrochemical oxidation producing the following intermediates BH2(OH)2-, BH(OH)3- and B(OH)4-, which is the final product. Multiple electrochemical methods have been used to uncover the properties of DMAB oxidation progress and verify above-mentioned hypothesis. Electrochemical Impedance Spectroscopy (EIS) was used to test the uncompensated resistance between the working electrode and reference electrode and calibrated in the following experiments: Cyclic voltammetry (CV) showed that DMAB in hydroxide electrolytes have three half-wave potentials with E_(1/2) of -0.778, -0.174 and 0.248 V. Kinetic current values obtained from the Koutecky-Levich plot decreased with temperature with -4.065, -3.62 and -1.45 mA/cm2 at 25°C, 41°C and 52°C, respectively. Rotating Disk Electrode (RDE) and Chronoamperometry (CA) were used to determine the Diffusion Coefficient of BH3(OH)-; BH2(OH)2- and BH(OH)3- 1.38E-05, 3.31E-05 and 1.01E-04, respectively. Tafel analysis was used in obtaining the transfer coefficient, whereas Klingler and Kochi’s method evaluated the constant. These kinetic parameters were used in KISSA-1D software to simulate the CVs. Gas Chromatography with Mass Spectrometry (GC/MS) was used to verify the existence of B(OH)4- and a peak at m/z 78.8 was recorded. All of this provided evidence that the three intermediates are involved in the proposed mechanism. In the future, simulated and experimental approaches will be investigated for other amine boranes compounds such as Sodium cyanoborohydride (NaBH3CN), Sodium triacetoxyborohydride (NaBH(O2CCH3)3), and Sodium borohydride (NaBH4). This work will have far-reaching consequences in enhancing the practical applications of gold and nickel in microelectronics and fuel cells.

Centrifugation forced ice-concentrate separation to enhance suspension freezing desalination performance

Suspension freeze desalination is a promising route for treatment of high salinity wastewater, but the poor ice-concentrate separation often generates decrease of desalination efficiency. In this work, it is demonstrated that centrifugation forced dewatering can assist in ice purification and enhance suspension freeze desalination performance. The positive correlation and good linear fitting relationship between ice purity and dewatering rate were identified at various centrifugation speeds, centrifugation time, and ice layer thickness. Changes of ice shape were recorded by low-temperature optical microscope observation system. The free water removal and ice floc destruction induced by centrifugal field have an important contribution to ice purification. Increasing centrifugation speed from 100 r/min to 500 r/min, the corresponding relative centrifugal force increased 27-fold, creating sharp increases in ice purity (rate constant k = 0.1605) and dewatering rate (rate constant D = 0.0563). Due to the strong binding characteristics and small portion of bound water, ice desalination efficiency per unit centrifugal force dropped when centrifugation speed increased from 1000 r/min to 3000 r/min. Besides, the multi-step dewatering and purification mechanism involved in ice centrifugation was depicted. The suspension freeze technology hybrid with centrifugation not only enhances desalination efficiency but also is beneficial to obtain high-purity ice.

Structural Framework for Analysis of CD4+ T-Cell Epitope Dominance in Viral Fusion Proteins.

Antigen conformation shapes CD4+ T-cell specificity through mechanisms of antigen processing, and the consequences for immunity may rival those from conformational effects on antibody specificity. CD4+ T cells initiate and control immunity to pathogens and cancer and are at least partly responsible for immunopathology associated with infection, autoimmunity, and allergy. The primary trigger for CD4+ T-cell maturation is the presentation of an epitope peptide in the MHC class II antigen-presenting protein (MHCII), most commonly on an activated dendritic cell, and then the T-cell responses are recalled by subsequent presentations of the epitope peptide by the same or other antigen-presenting cells. Peptide presentation depends on the proteolytic fragmentation of the antigen in an endosomal/lysosomal compartment and concomitant loading of the fragments into the MHCII, a multistep mechanism called antigen processing and presentation. Although the role of peptide affinity for MHCII has been well studied, the role of proteolytic fragmentation has received less attention. In this Perspective, we will briefly summarize evidence that antigen resistance to unfolding and proteolytic fragmentation shapes the specificity of the CD4+ T-cell response to selected viral envelope proteins, identify several remarkable examples in which the immunodominant CD4+ epitopes most likely depend on the interaction of processing machinery with antigen conformation, and outline how knowledge of antigen conformation can inform future efforts to design vaccines.

The utilization of bio-ethanol for production of 1-butanol catalysed by Mg–Al mixed metal oxides enhanced by Cu or Co

The Guerbet reaction is a possible way for transformation of ethanol to 1-butanol (important for many kinds of industries), which consists of four steps: dehydrogenation, aldol condensation, dehydration, and hydrogenation. Due to the elimination of possible side-reactions, the selective catalysis is required to favour production of 1-butanol at temperature below 350 °C. The main aim of this work was the ethanol transformation via heterogeneous catalysis using active Mg–Al mixed oxides with copper or cobalt carried out in the microflow reactor in the reaction temperature interval 280–350 °C. The novelty lies in the statistical analysis of results from characterization of catalyst structure and surface with catalysis results providing more sophisticated perspective on the ethanol valorization. The series of Mg–Al catalysts containing copper showed an overall higher conversion of ethanol and selectivity to butanol compared to the series containing cobalt. Major difference of catalytic activity was at low reaction temperatures and at a lower copper content in the Mg–Al matrix, which is significant from the point of view of environmentally clean processes. A multi-step mechanism of the Guerbet reaction involving an aldol condensation was verified for both tested catalysts series and reaction conditions.Graphic abstractValorization of bio-ethanol to 1-butanol by Mg-Al mixed metal oxides enhanced by Cu or Co

Electrocatalytic reduction of Cr(VI) on gold-based electrodes in acidic medium: A systematic approach to chromium detection

In the present research, gold immobilized on different substrates (Au, GC, Pt) was examined to fabricate a Cr(VI) sensor in an acidic medium via reduction reactions. Comparative analysis revealed that Au-Pt electrode exhibited better electrocatalytic activity towards the reduction of Cr(VI) compared to Au, Au-Au or Au-GC electrode, which is emphatically discussed in this article. Specifically, the inner α-Au2O3 species of Au matrix on the catalytic surface played a key role in catalyzing Cr(VI) in the acidic medium. Voltammetric investigations revealed that the concerned electrode process is proton-dependent. From hydrodynamic voltammetric studies, it was found that the reduction reaction follows a multistep reaction mechanism with a single electron transfer rate-determining step over the Au-Pt surface. The Cr(VI) reduction reaction follows 1st order kinetics at the Au-Pt electrode surface, where the standard rate constant (k) was found to be 1.4×10−2 cm−1. The excellent improvement of reduction current over the Au-Pt surface was exploited in the fabrication of the Cr(VI) sensor. The developed sensor detects Cr(VI) ions with a linear dynamic range of 10 to 130 μM, whereas the sensitivity and limit of detection values are 3.21 μAμM−1cm−2 and 2.97 μM, respectively. Overall, the findings highlight the promising performance of the Au-Pt electrode in detecting Cr(VI) ions and provide valuable insights into the underlying catalytic diagnosis.