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The efficiency of many processes strongly depends on their thermodynamic reversibility, i.e., proximity to equilibrium throughout the process. In thermochemical cycles for water and/or carbon dioxide splitting, thermochemical air separation, and thermochemical energy storage, operating near equilibrium means that the oxygen chemical potential of the solid and gas phases must not differ significantly. We show that approaching this ideal is possible in thermal reduction only if the reaction step occurs at a specific, reaction coordinate- and material-dependent temperature. The resulting thermal reduction temperature profile also depends on the ratio of gas and solid flows.

Methylation of aromatic compounds is a key reaction step in various industrial processes such as the aromatic cycle of methanol-to-hydrocarbons chemistry. The study of isolated methylation reactions and of the influence of catalyst acidity on their kinetics is a challenging task. Herein, we have studied unidirectional metal-substituted H-MeAlPO-5 materials to evaluate the effect of acid strength on the kinetics of benzene methylation with DME. First-principle simulations showed a direct correlation between the methylation barrier and acid site strength, which depends on the metal substituent. Three H-MeAlPO5 catalysts with high (Me = Mg), moderate (Me = Si) and low acidity (Me = Zr) were experimentally tested, confirming a linear relationship between the methylation activation energy and acid strength. The effects of temperature and reactant partial pressure were evaluated, showing significant differences in the byproduct distribution between H-MgAlPO-5 and H-SAPO-5. Comparison with propene methylation suggested that the Mg substituted catalyst is also the most active for the selective methylation of alkenes. (c) 2021 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Elucidating the elementary kinetics of nitrogen reduction on transition metal surfaces can guide the search for materials capable of efficiently catalysing electrochemical ammonia synthesis at ambient conditions. Density functional theory calculations are used here to explore the elementary kinetics of nitrogen reduction and hydrogen evolution on W(110). All proton-electron transfer barriers are calculated at −0.7 V vs. SHE, where the cathodic potential is explicitly modelled using a solvation bilayer of water with hydronium ions. The protonation of adsorbed NH is determined to be rate-limiting for nitrogen reduction, with a barrier of 0.65 eV. The same reaction step is potential-limiting based on the thermochemistry of adsorbed intermediates only, showing that thermochemical calculations suffice to predict catalytic trends for nitrogen reduction. The largest barrier found for hydrogen evolution at high hydrogen coverage is 0.36 eV. Thus, hydrogen evolution is expected to dominate over nitrogen reduction on W(110) at negative potentials.

The freshwater alga Spirogyra crassa was subjected to pyrolysis to investigate its potential use as a bioenergy feedstock. To do so, the pyrolysis behavior of the Spirogyra crassa under thermogravimetric scale was first determined at the temperature range from 25 to 800 °C, with three slow heating rates (5, 10, and 20 °C min−1) under an oxygen-free atmosphere. It is assumed that the pyrolysis of Spirogyra crassa occurs in four reaction steps with different kinetic triplets. The activation energy was obtained for each reaction step by concurrent use of four isoconversional methods (Friedman, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, and Starink), with average values ranging from 120.6 to 217.0 kJ mol−1. Pre-exponential factors determined from the kinetic compensation effect were found to range between 6.88 × 107 and 7.54 × 1019 min−1. Master plot results indicated that the nth-order-based mechanisms described the pyrolysis behavior of organic matter and, subsequently, the pyrolysis behavior of inorganic matter follows Avrami-Erofeev nucleation mechanisms. According to the thermodynamics parameters, the pyrolysis of Spirogyra crassa verifies to be a non-spontaneous, endothermic, and complex conversion. The summative kinetic expression proposed from the estimated kinetic triplets is a satisfactory option for describing the pyrolysis kinetics of Spirogyra crassa, with a quality of adjustment above 93.3 %. In conclusion, the insights of this study confirm that Spirogyra crassa has considerable potential as a feedstock for bioenergy production, and could be used for engineering purposes in the design or simulation of large-scale pyrolysis reactors.

Biaryls have widespread applications in organic synthesis. However, sequentially polysubstituted biaryls are underdeveloped due to their challenging preparation. Herein, we report the synthesis of dissymetric 2,3,2',3',4-substituted biaryls via pericyclic reactions of cyclic diaryl λ3-bromanes. The functional groups tolerance and atom economy allow access to molecular complexity in a single reaction step. Continuous flow protocol has been designed for the scale-up of the reaction, while postfunctionalizations have been developed taking advantage of the residual Br-atom.

During the reduction of molybdenum trioxide (MoO3 ) to metallic molybdenum, the first reduction step yielding molybdenum dioxide as an intermediary product is of crucial importance. In this study, we examined the impact of the parameters reduction temperature, water influx, and potassium content on the hydrogen reduction of this first reaction step. Beginning from the same starting material, the chemical vapor transport mechanism was utilized to yield the phase pure MoO2 . Analyses including powder X-ray diffraction, inductively coupled plasma-mass spectrometry, scanning electron microscopy, and high performance optical microscopy were performed on the product phases. Modulations of the specific surface areas of molybdenum dioxide ranging from 2.28 to 0.41 m2 /g were possible. Furthermore, a distinct shift from small plate-like grains to cuboid-like forms was achieved.

The chemi-ionization of Ar, Kr, N2, H2, and D2 by Ne(3P2) and of Ar, Kr, and N2 by He(3S1) was studied by electron velocity map imaging (e-VMI) in a crossed molecular beam experiment. A curved magnetic hexapole was used to state-select the metastable species. Collision energies of 60 meV were obtained by individually controlling the beam velocities of both reactants. The chemi-ionization of atoms and molecules can proceed along different channels, among them Penning ionization and associative ionization. The evolution of the reaction is influenced by the internal redistribution of energy, which happens at the first reaction step that involves the emission of an electron. We designed and built an e-VMI spectrometer in order to investigate the electron kinetic energy distribution, which is related to the internal state distribution of the ionic reaction products. The analysis of the electron kinetic energy distributions allows an estimation of the ratio between the two-reaction channel Penning and associative ionization. In the molecular cases the vibrational or electronic excitation enhanced the conversion of internal energy into the translational energy of the forming ions, thus influencing the reaction outcome.

Halodefluorination of alkyl fluorides using group 13 metal halides has been known for quite some time (first reported by Newman in 1938) and is often utilized in its crude stoichiometric form to substitute fluorine with heavier halogens. However, recently halodefluorination has undergone many developments. The reaction can be effected with a range of metal halide sources (including s-block, f-block, and p-block metals), and has been developed into a catalytic process. Furthermore, methods for monoselective halodefluorination in polyfluorocarbons have been developed, allowing exchange of only a single fluorine with a heavier halogen. The reaction has also found use in cascade processes, where the final product may not even contain a halide, but where the conversion of fluorine to a more reactive halogen is a pivotal reaction step in the cascade. This review provides a summary of the developments in the reaction from its inception until now.1 Introduction2 Stoichiometric Halodefluorination2.1 Group 13 Halodefluorination Reagents2.2 Other Metal Halide Mediated Halodefluorination3 Catalytic Halodefluorination4 Monoselective Halodefluorination5 Cascade Reactions Involving Halodefluorination6 Summary and Outlook

The efficiency of CO2 methanation was estimated through gas chromatography in the presence of Co–Fe catalysts. Scanning electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy were applied for ex-situ analysis of the catalysts after their test in the methanation reaction. Thermal programmed desorption mass spectroscopy experiments were performed to identify gaseous species adsorbed at the catalyst surface. Based on the experimental results, surface reaction model of CO2 methanation on Co–Fe catalysts was proposed to specify active ensemble of metallic atoms at the catalyst surface, orientation of adsorbed CO2 molecule on the ensemble and detailed reaction mechanism of CO2→CH4 conversion. The reaction step when OH group in the FeOOH complex recombined with the H atom adsorbed at the active ensemble to form H2O molecule was considered as the rate-limiting step.

The new, standard molecular biologic system for duplicating DNA enzymatically devoid of employing a living organism, like E. coli or yeast, represents polymerases chain reaction (PCR). This technology allows an exponential intensification of a minor quantity of DNA molecule several times. Analysis can be straightforward with more DNA available. A thermal heat cycler performs a polymerization chain reaction that involves repeated cycles of heating and cooling the reactant tubes at the desired temperature for each reaction step. A heated deck is positioned on the upper reaction tube to avoid evaporating the reaction mixture (normally volumes range from 15 to 100 l per tube), or an oil layer can be placed on a reaction mixture surface. The amplified DNA fragment is determined based on selecting primers in addition to the starting and end of the DNA fragment. The primers stand for short, artificial DNA stripes, no higher than fifty (typically 18-25bp) nucleotides have been based on a starting and ending of DNA fragment to be amplified. DNA-polymerase connects and starts a new DNA strand synthesis The PCR products can be visualized by dual foremost methods: (1) staining of the product of DNA amplified by a chemical dye like bromide ethidium, or (2) marking of fluorescent dyes (fluorophores) PCR primers or nucleotides before amplification of PCRs. PCR offers some benefits. First, it is a simple method of understanding and using and quick results. It has an extremely sensitive technology with the potential for sequencing, cloning, and analyzing millions or milliards of copies of a particular product.

Radical-induced 1,2-metallate rearrangements of boronate complexes are an emerging and promising class of reactions that allow multiple new bonds to be formed in a single, tuneable reaction step. These reactions involve the addition of an alkyl radical, typically generated from an alkyl iodide under photochemical activation, to a boronate complex to produce an α-boryl radical intermediate. From this α-boryl radical, there are two plausible reaction pathways that can trigger the product forming 1,2-metallate rearrangement: iodine atom transfer (IAT) or single electron transfer (SET). Previous steady state techniques have struggled to differentiate these pathways. Here we apply state-of-the-art time-resolved infrared absorption spectroscopy to resolve all the steps in the reaction cycle, by mapping production and consumption of the reactive intermediates over picosecond to millisecond timescales. We apply this technique to a recently reported reaction involving the addition of an electron-deficient alkyl radical to the strained σ‑bond of a bicyclo[1.1.0]butyl boronate complex to form a cyclobutyl boronic ester. We show that the previously proposed SET mechanism does not adequately account for the observed spectral and kinetic data. Instead, we demonstrate that IAT is the preferred pathway for this reaction and is likely to be operative for other reactions of this type.

We synthesized a series of carbon-supported atomic metal-N-C catalysts (M-SACs: M=Mn, Fe, Co, Ni, Cu) with similar structural and physicochemical properties to uncover their catalytic activity trends and mechanisms. The peroxymonosulfate (PMS) catalytic activity trends are Fe-SAC>Co-SAC>Mn-SAC>Ni-SAC>Cu-SAC, and Fe-SAC displays the best single-site kinetic value (1.65×105 min-1 mol-1 ) compared to the other metal-N-C species. First-principles calculations indicate that the most reasonable reaction pathway for 1 O2 production is PMS→OH*→O*→1 O2 ; M-SACs that exhibit moderate and near-average Gibbs free energies in each reaction step have a better catalytic activity, which is the key for the outstanding performance of Fe-SACs. This study gives the atomic-scale understanding of fundamental catalytic trends and mechanisms of PMS-assisted reactive oxygen species production via M-SACs, thus providing guidance for developing M-SACs for catalytic organic pollutant degradation.

GeoChemFoam is an open-source OpenFOAM-based toolbox that includes a range of additional packages that solve various flow processes from multiphase transport with interface transfer, to single-phase flow in multiscale porous media, to reactive transport with mineral dissolution. In this paper, we present a novel multiphase reactive transport solver for simulations on complex pore geometries, including microfluidic devices and micro-CT images, and its implementation in GeoChemFoam. The geochemical model includes bulk and surface equilibrium reactions. Multiphase flow is solved using the Volume-Of-Fluid method, and the transport of species is solved using the continuous species transfer method. The reactive transport equations are solved using a sequential operator splitting method, with the transport step solved using GeoChemFoam, and the reaction step solved using Phreeqc, the US geological survey’s geochemical software. The model and its implementation are validated by comparison with analytical solutions in 1D and 2D geometries. We then simulate multiphase reactive transport in two test pore geometries: a 3D pore cavity and a 3D micro-CT image of Bentheimer sandstone. In each case, we show the pore-scale simulation results can be used to develop upscaled models that are significantly more accurate than standard macro-scale equilibrium models.

The atomistic mechanism of dissolution reactions at mineral fluid interface is essential for understanding the reaction kinetics and the adsorption and thermodynamic equilibria at mineral surfaces. In this study we investigate the initial state of the dissolution process on (0 1 0) surface of pyrophyllite at elevated pressure by applying large-scale ab initio Meta-Dynamics simulations. The system setup provides a realistic representation of the clay mineral edge surface structure and takes into account explicit dynamics of solvent molecules. The model parameters follow the procedure recently tested for the simulation of the (1 1 0) pyrophyllite edge. The simulation reveals that dissolution of a single tetrahedral or an octahedral unit from the clay mineral edge is a complex multi-step process with several reaction intermediates. Typically, each reaction step changes the denticity of the reacting site in a step-by-step manner and leads, eventually, to the leaching of the ions forming the octahedral and tetrahedral sheets of the phyllosilicate. The solvent rearrangement and the proton transfer reactions in the first and second coordination shell of the dissolving unit play a critical role in the stabilization of reaction intermediates and the net progress of the dissolution reactions. In contrast to ambient conditions, the transition complexes formed during the dissolution at elevated conditions were found to have an increased coordination number. The simulation reveals new insight into the coordination environment of the dissolving complexes at the mineral fluid interface.

The present study investigates freely propagating methane/hydrogen lean-premixed laminar flames at elevated pressures to understand the hydrogen addition effect of natural gas on the NO formation under the conditions of industrial gas turbine combustors. The detailed chemical kinetic model which was used in the previous study on the NO formation in high pressure methane/air premixed flames was adopted for the present study to analyze NO formation of methane/hydrogen premixed flames. The present mechanism shows good agreement with experimental data for methane/hydrogen mixtures, including ignition delay times, laminar burning velocities, and NO concentration in premixed flames. Hydrogen addition to methane/air mixtures with maintaining methane content leads to the increase of NO concentration in laminar premixed flames due to the higher flame temperature. Methane/hydrogen/argon/air premixed flames are simulated to avoid the flame temperature effect on NO formation over a pressure range of 1–20atm and equivalence ratio of 0.55. Kinetic analyses shows that the N2O mechanism is important on NO formation for lean flames between the reaction zone and postflame region, and thermal NO is dominant in the postflame zone. The hydrogen addition leads to the increase of NO formation from prompt NO and NNH mechanisms, while NO formation from thermal and N2O mechanisms are decreased. Additionally, the NO formation in the postflame zone has positive pressure dependencies for thermal NO with an exponent of 0.5. Sensitivity analysis results identify that the initiation reaction step for the thermal NO and the N2O mechanism related reactions are sensitive to NO formation near the reaction zone.

1,4-Hydroxycarbonyls can potentially undergo sequential reactions involving cyclization followed by dehydration to form dihydrofurans. As dihydrofurans contain a double bond, they are highly reactive toward atmospheric oxidants such as OH, O3, and NO3. In the present study, we use ab initio calculations to examine the impact of various atmospheric catalysts on the energetics and kinetics of the gas-phase cyclization and dehydration reaction steps associated with 4-hydroxybutanal, a prototypical 1,4-hydroxycarbonyl molecule. The cyclization step transforms 4-hydroxybutanal into 2-hydroxytetrahydrofuran, which can subsequently undergo dehydration to form 2,3-dihydrofuran. As the barriers associated with the cyclization and dehydration steps for 4-hydroxybutanal are, respectively, 34.8 and 63.0 kcal/mol in the absence of a catalyst, both reaction steps are inaccessible under atmospheric conditions in the gas phase. However, the presence of a suitable catalyst can significantly reduce the reaction barriers, and we have examined the impact of a single molecule of H2O, HO2 radical, HC(O)OH, HNO3, and H2SO4 on these reactions. We find that H2SO4 reduces the reaction barriers the greatest, with the barrier for the cyclization step being reduced to -13.1 kcal/mol and that for the dehydration step going down to 9.2 kcal/mol, measured relative to their respective separated starting reactants. Interestingly, our kinetic study shows that HNO3 gives the fastest rate due to the combined effects of a larger atmospheric concentration and a reduced barrier. Thus, our study suggests that, with acid catalysis, the cyclization reaction step can readily occur for 1,4-hydroxycarbonyls in the gas phase. Because the dehydration step exhibits a significant barrier even with acid catalysis, the 2-hydroxytetrahydrofuran products, once formed, are likely lost through their reaction with OH radicals in the atmosphere. We have investigated the reaction pathways and the rate constant for this bimolecular reaction in the presence of excess molecular oxygen (3O2), as it would occur under tropospheric conditions, using computational chemistry over the 200-300 K temperature range. We find that the main products from these OH-initiated oxidation reactions are succinaldehyde + HO2 and 2,3-dihydro-2-furanol + HO2.

The thermal behavior of perlite concrete, which is used in sodium-cooled fast reactor plants, was subjected to kinetic modeling to gather the fundamental data for establishing a reliable safety assessment system. In this study, the influence of atmospheric CO2 on the multistep kinetic behavior of perlite concrete was investigated in detail by separating the component reaction steps using kinetic deconvolution analysis (KDA) based on a cumulative kinetic equation. The carbonation of Ca(OH)2 during its thermal decomposition was identified as a specific process observed in the presence of atmospheric CO2. The process was characterized by KDA as the successive thermal decomposition of Ca(OH)2 to form CaO and the subsequent carbonation of CaO. A shift in the temperature range of the overall carbonation process to higher temperatures with increase in partial pressure of CO2 (p(CO2)) was also identified as a specific phenomenon. The thermal decomposition of CaCO3 was separated from the multistep thermal decomposition of the perlite concrete using KDA and analyzed kinetically considering the influence of p(CO2). A universal kinetic description over different temperatures and p(CO2) values was achieved by introducing an accommodation function composed of p(CO2) and the equilibrium CO2 pressure for the reaction. Introduction of the modified kinetic equation with the accommodation function into the corresponding reaction step of the cumulative kinetic equation enables a universal kinetic description of the overall thermal decomposition of perlite concrete over different temperature and p(CO2) conditions.

This review highlights methods for the synthesis of five- and six-membered heterocycles and their annulated analogues. These methods are based on anionic domino reactions that have a common step: an SN2/Thorpe–Ziegler reaction. In addition, data on the biological activity of these heterocycles are summarized.1 Introduction2 Synthesis of Thiophenes, Pyrroles, Furans and Other Heterocycles2.1 Synthesis of 3-Aminothiophenes2.2 Synthesis of 3-Aminopyrroles2.3 Synthesis of 3-Aminofurans3 Synthesis of Bicyclic Heterocyclic Systems3.1 Thiophenes, Pyrroles and Furans Fused with Five-Membered Heterocycles3.2 Thiophenes, Pyrroles and Furans Fused with Six-Membered Heterocycles4 Synthesis of Heterocyclic Compounds Using Three-Step Domino Reactions5 Synthesis of Heterocyclic Compounds Based on a Combination of Two Domino Reactions6 Miscellaneous7 Conclusion

The demand for decarbonizing the ammonia industry by using renewable energy has invoked increasing research interests into catalyst development for effective N2 reduction under mild conditions. Hydride-based materials are among some of the emerging catalysts for ammonia synthesis at ambient pressure and low temperatures (

Transition metal- and nitrogen-codoped graphene (referred to as M-N-G, where M is a transition metal) has emerged as an important type of single-atom catalysts with high selectivities and activities for electrochemical CO2 reduction (CO2 R) to CO. However, despite extensive previous studies on the catalytic origin, the active site in M-N-G catalysts remains puzzling. In this study, density functional theory calculations and computational hydrogen electrode model is used to investigate CO2 R reaction energies on Zn-N-G, which exhibits outstanding catalytic performance, and to examine kinetic barriers of reduction reactions by using the climbing image nudged elastic band method. We find that single Zn atoms binding to N and C atoms in divacancy sites of graphene cannot serve as active sites to enable CO production, owing to *OCHO formation (* denotes an adsorbate) at an initial protonation process. This contradicts the widely accepted CO2 R mechanism whereby single metal atoms are considered catalytic sites. In contrast, the C atom that is the nearest neighbor of the single Zn atom (CNN ) is found to be highly active and the Zn atom plays a role as an enhancer of the catalytic activity of the CNN . Detailed analysis of the CO2 R pathway to CO on the CNN site reveals that *COOH is favorably formed at an initial electrochemical step, and every reaction step becomes downhill in energy at small applied potentials of about -0.3 V with respect to reversible hydrogen electrode. Electronic structure analysis is also used to elucidate the origin of the CO2 R activity of the CNN site.

A facile tandem route has been developed for constructing quinazolinones from various aminobenzamides and in-situ generated aldehydes. Visible light was found to play a dual role: first oxidizes the alcohol to the aldehyde and then facilitates its cyclization with o-substituted aniline. Furthermore, alcohols are perfect alternatives to aldehydes because they are greener, more available, more economical, more stable, and less toxic than aldehydes. The first reaction step continuously provides material for the second step, which effectively reduces loss through volatilization, oxidation, and polymerization of the aldehyde, while avoiding its toxicity. A variety of quinazolinones can be prepared in the presence of visible light without any additional photocatalyst. The developed synthesis protocol proceeds with the merits of mild conditions, broad substrate scope, operational simplicity, and high atom efficiency, with an eco-energy source under metal-free, photocatalyst-free, and ambient conditions.

Density functional theory and high-level ab initio electronic structure calculations are performed to study the mechanism of the partial oxidation of methane to methanol facilitated by the titled anionic transition metal atoms. The energy landscape for the overall reaction M- + N2O + CH4 → M- + N2 + CH3OH (M = Fe, Ni, Pd, Pt) is constructed for different reaction pathways for all four metals. The comparison with earlier experimental and theoretical results for cationic centers demonstrates the better performance of the metal anions. The main advantage is that anionic centers interact weakly with the produced methanol. This fact facilitates the fast removal of methanol from the catalytic center and prevents the overoxidation of methane. Moreover, a moderate or high energy barrier for the M- + CH4 → HMCH3- reaction step is observed, which protects the metal center from deactivation. Future work should focus on the identification of proper ligands, which stabilize the negative charge on the metal (electronic factors) and prevent the formation of the global CH3MOH- minimum (steric factors). Finally, a composite electronic structure method (combining size extensive coupled clusters approaches and accurate multireference configuration interaction) is proposed for computationally demanding systems and is applied to Fe-.

Focused electron beam deposition often requires the use of purification techniques to increase the metal content of the respective deposit. One of the promising methods is adding H2O vapor as a reactive agent during the electron irradiation. However, various contrary effects of such addition have been reported depending on the experimental condition. We probe the elementary electron-induced processes that are operative in a heterogeneous system consisting of iron pentacarbonyl as an organometallic precursor and water. We use an electron beam of controlled energy that interacts with free mixed Fe(CO)5/H2O clusters. These mimic the heterogeneous system and, at the same time, allow direct mass spectrometric analysis of the reaction products. The anionic decomposition pathways are initiated by dissociative electron attachment (DEA), either to Fe(CO)5 or to H2O. The former one proceeds mainly at low electron energies ( 6 eV), where the DEA to H2O forms OH- in the first reaction step. This intermediate reacts with Fe(CO)5, leading to enhanced decomposition, with the desorption of up to three CO ligands. The present results demonstrate that the water action on Fe(CO)5 decomposition is sensitive to the involved electron energy range and depends on the hydration degree.

Summary Efficient strategies to assemble enantioenriched pyridine derivatives are highly important, given their significance in both synthetic and medicinal chemistry. Here, we report an enantioselective nickel-catalyzed intermolecular [2 + 2 + 2] cycloaddition of alkyne-tethered malononitriles with alkynes for the synthesis of densely substituted pyridines. The α-all-carbon quaternary center adjacent to pyridine is introduced by desymmetrizing the two cyano groups of disubstituted malononitriles. Notably, terminal alkynes are also tolerated with good regioselectivity to afford tetrasubstituted pyridines. Zinc halide is essential to enable the occurrence of the transformation by promoting the hetero-cyclometallation step. The reaction uses bio-renewable 2-MeTHF as the solvent and features mild reaction conditions, good functional group compatibilities, and enantioselectivities. This study offers a straightforward approach to the valuable enantioenriched heteroarenes from feedstock chemicals by forming three bonds and one quaternary stereocenter simultaneously in a single reaction step.

The typical layered transition metal dichalcogenide (TMDC) material, MoS2, is considered a promising candidate for the next-generation electronic device due to its exceptional physical and chemical properties. In chemical vapor deposition synthesis, the sulfurization of MoO3 powders is an essential reaction step in which the MoO3 reactants are converted into MoS2 products. Recent studies have suggested using an H2S/H2 mixture to reduce MoO3 powders in an effective way. However, reaction mechanisms associated with the sulfurization of MoO3 by the H2S/H2 mixture are yet to be fully understood. Here, we perform quantum molecular dynamics (QMD) simulations to investigate the sulfurization of MoO3 flakes using two different gaseous environments: pure H2S precursors and a H2S/H2 mixture. Our QMD results reveal that the H2S/H2 mixture could effectively reduce and sulfurize the MoO3 reactants through additional reactions of H2 and MoO3, thereby providing valuable input for experimental synthesis of higher-quality TMDC materials.

Aldehyde deformylation is an important reaction in biology, organic chemistry and inorganic chemistry and the process has been widely applied and utilized. For instance, in biology the aldehyde deformylation reaction has wide differences in biological function, whereby cyanobacteria convert aldehydes into alkanes or alkenes, which are used as natural products for, e.g., defense mechanisms. By contrast, the cytochromes P450 catalyse the biosynthesis of hormones, such as estrogen, through an aldehyde deformylation reaction step. In organic chemistry, the aldehyde deformylation reaction is a common process for replacing functional groups on a molecule, and as such, many different synthetic methods and procedures have been reported that involve an aldehyde deformylation step. In bioinorganic chemistry, a variety of metal(III)-peroxo complexes have been synthesized as biomimetic models and shown to react efficiently with aldehydes through deformylation reactions. This review paper provides an overview of the various aldehyde deformylation reactions in organic chemistry, biology and biomimetic model systems, which shows a broad range of different chemical reaction mechanisms for this process. Although a nucleophilic attack at the carbonyl centre is the consensus reaction mechanism, however, several examples of an alternative electrophilic reaction mechanism starting with hydrogen atom abstraction have been reported as well. There is still much to learn and to discover on aldehyde deformylation reactions, as deciphered in this review paper.

The Suzuki–Miyaura coupling reaction of electron-poor aryl chlorides in the synthesis of crop protection-relevant active ingredients in water is disclosed. Optimisation of the reaction conditions allowed running the reaction with 50 ppm of Pd-catalyst loading without an additional organic solvent in the cross-coupling reaction step in short reaction times. The system was optimised for the initial cross-coupling step of the large scale produced fungicides Boscalid, Fluxapyroxad and Bixafen up to 97% yield. It is also shown that the Suzuki–Miyaura reaction can be easily scaled up to 50 g using a simple product separation and purification using environmentally benign solvents in the work-up. To show the usability of this method, it was additionally applied in the three-step synthesis of the desired active ingredients.

Amorphous nickel–iron mixed metal oxides have been shown to be extremely efficient oxygen evolution reaction (OER) electrocatalysts with good stability in alkaline reaction conditions. Thus, they offer an economical alternative to expensive conventional platinum- or iridium-based OER catalysts and could provide a crucial step towards a hydrogen-based energy economy. These favorable properties are presumably due to a synergistic effect between Fe and Ni. However, these synergistic effects strongly depend on the local structure of the catalyst and their origin – and its relation to the local structure – are still not fully understood. In this work we present a study of the thermal annealing induced structural evolution of amorphous (Ni,Fe)Ox thin films, and correlate this evolution to their OER catalytic capabilities. Samples are X-ray amorphous at low annealing temperatures. However, analysis of the X-ray absorption spectra reveals local structural transitions in all samples – before the onset of crystallization – providing evidence of polyamorphism. Transitions of the local Ni and Fe environments occur at distinctly different temperatures and coincide with a stepwise increase in the catalytic activation potential (OER thermodynamics) and the Tafel slope (OER kinetics), respectively. We previously have attributed the increase in onset potential to a change in active site in NiOx at the phase transition temperature; considering that the mixed metal oxides' onset potentials exhibit the same behavior with annealing temperature (Tanneal), we conclude that the potential-determining OER reaction step must occur at a Ni site. Similarly, the reaction kinetics change at the same annealing temperature as the local Fe environment; we thus infer that the rate-determining step occurs at a Fe site. To reconcile these observations we put forward a dual-site OER reaction mechanism with potential- and rate-determining steps happening at Ni and Fe sites, respectively. This synergistic effect is ultimately responsible for the superior OER performance of many (Ni,Fe)Ox catalysts. At higher annealing temperatures, the synergistic effect is suppressed, possibly by phase separation into NiOx and FeOx phases, as suggested by our X-ray diffraction results.

This work demonstrates a novel approach to add value to pyrolysis liquids by exploiting the diverse range of alcohol functional groups present within the mixture to yield a non-energy product, without requiring extensive separation. It is shown that 79.2% of the alcohol functional groups can be converted by esterification and subsequently polymerised (85.7%) to produce a range of polymer products with peak molecular weight (Mp) ranging from 22.9–36.9 kDa. Thermal and rheological properties of the most promising pyrolysis material have been compared with conventional poly(butyl methacrylate) (pBMA) of similar molecular weight, showing viability as a potential replacement owing to similarities in its thermorheological behaviour. A low molecular weight wax component of the novel polymer has been identified as a possible plasticizing agent, causing some decreases in viscosity. Production of the monomer is achieved in one reaction step and without separation or the use of toxic reagents. The overall mass balance and relevance to a biorefinery process is highlighted and strategies to tune the process to vary glass transition temperature (Tg) and Mp are discussed.

Constructing efficient catalysts for N2 reduction into value added ammonia under ambient conditions is a considerable challenge. Herein, well-defined single-site metal–organic frameworks (MOFs, M–TCPP; M = Fe, Co, or Zn) were constructed and evaluated as electrocatalysts for N2 reduction. The prepared Fe–TCPP exhibited prominent performance with a high NH3 yield of 44.77 μg h−1 mgcat.−1 and a faradaic efficiency of 16.23%, superior to that of all the reported molecular and MOF catalysts. The superior performance was ascribed to the highly effective N2 activation at the Fe site, and benefited from the overall reaction thermodynamics advantage in the key reaction step of *NNH formation. This study gives an understanding of the intrinsic activity of well-defined catalysts in the electrocatalytic N2 reduction, and provides atomic-level insights into the rational design and engineering of highly active catalysts for artificial N2 fixation.

Conjugation of protein therapeutics with polymers like polyethylene glycol (PEG) has been shown to increase their therapeutic efficiency. However, manufacturing of PEGylated drugs requires an additional, carefully controlled reaction step after purifying the protein, followed by further purification of over- and under-PEGylated variants. In this work, we have used a combined spectroscopic and statistical approach for monitoring and control of the PEGylation reaction for G-CSF using near infrared spectroscopy (NIRS). An online NIRS probe deployed in the reaction vessel has been used to track conversion of G-CSF into monoPEGylated and multiPEGylated forms using calibrated partial least squares regression models on the NIRS spectra which are collected in real time every 3 s. A pH probe integrated with a peristaltic pump facilitates automated quenching of the reaction at the targeted time. The NIRS spectra have also been used to build a batch evolution model for the reaction from end-to-end, including the addition of the reactants to the reaction vessel, the progress of the reaction for 70 min, and the final quenching with Tris base. Online spectra are compared against the statistical process control charts of the batch evolution model in real time to detect deviations as soon as they occur. The system was demonstrated for four common deviations in the PEGylation process, namely: delayed quenching time, wrong concentration of reducing agent added, wrong PEG to G-CSF ratio, and wrong sequence of addition of reactants. The system was able to identify all four deviations in real time and alert the operator to take control actions. The PAT approach suggested here embraces the quality by design framework and can be generalized for manufacturing scale monitoring and control of different biotechnology reactions with spectroscopic signatures.

We report the oxidative coupling of methane (OCM) performance over Na2ZrO3 under various temperatures, CH4/O2 ratios, and reaction pressures. Sensitivity of CH4 conversion rate was investigated with respect to feed components CH4 and O2 pressures, as well as reaction products CO2 and H2O pressures. Kinetic data obtained under various conditions were fitted to establish an OCM reaction network to describe the product distribution based on the rate constants at each reaction step. Temperatures above 750 °C caused gradual decay in catalytic performance, likely due to Na loss associated with the transformation of Na2ZrO3 crystal phase to monoclinic ZrO2. This catalyst exhibited competitive inhibition by reversible CO2 adsorption and CO oxidation activity, both of which were necessary to include to construct an accurate kinetic model.

Molecular spatial conformational evolution following the corresponding chemical reaction pathway at surfaces is important to understand and optimize chemical processes. Combining experimental and theoretical methods, the sequential N-H and C-H dehydrogenation of pyromellitic diimide (PMDI) on a Cu(111) surface are reported. STM experiments and atomistic modeling allow structural analysis at each well-defined reaction step. First, exclusively the aromatic N-H dehydrogenation of the imide group is observed. Subsequently, the C-H group at the benzene core of PMDI gets activated leading to a dehydrogenation reaction forming metalorganic species where Cu adatoms pronouncedly protruding from the surface are coordinated by one or two PMDI ligands at the surface. All reactions of PMDI induce conformational changes at the surface as confirmed by STM imaging and DFT simulations. Such conformational evolution in sequential N-H and C-H activation provides a detailed insight to understand molecular dehydrogenation processes at surfaces.

NO dissociation is an important reaction step in the NO reduction reaction, particularly in the three-way catalyst conversion system for automotive gas exhaust purification. In this study, we used first-principles calculations based on density functional theory to analyze the interaction and dissociation of NO on the PdRuIr ternary alloy. The electronic properties of the atomic combination of the PdRuIr ternary alloy create an effective catalyst that is active for NO dissociation and relatively stable against the formation of volatile RuOx through a weakened O adsorption. This study also shows that for an alloyed system, the strength of NO adsorption may not necessarily predict the dissociation activity. This tendency is observed in the PdRuIr ternary alloy where Ru top is the active site for NO adsorption albeit not an effective site for dissociation. It is presumed that NO dissociation is mediated by its molecular diffusion to active sites for dissociation, which are usually high Ru- and/or Ir-coordinated hollow or bridge sites. These active sites allow high charge transfer from the surface to NO, which fills the NO anti-bonding state and facilitates dissociation. This therefore assumes that the strength of NO molecular adsorption is not a descriptor for NO dissociation on metal alloys but rather the ability of the surface to transfer charge to NO and homogeneity of the strength of adsorption. Furthermore, O adsorption on the ternary alloy, particularly near the Ru sites, is relatively weaker as compared to the pure Ru surface. This weakened O adsorption is attributed to charge re-distribution through alloying, particularly charge transfer from the Ru atom to the Ir and Pd atoms.

Glyoxalase I (GlxI) is an important enzyme that catalyzes the detoxification of methylglyoxal (MG) with the help of glutathione (H-SG). It is currently unclear whether MG and H-SG are substrates of GlxI or whether the enzyme processes hemithioacetal (HTA), which is nonenzymatically formed from MG and H-SG. Most previous studies have concentrated on the latter mechanism. Here, we study the two-substrate reaction mechanism of GlxI from humans (HuGlxI) and corn (ZmGlxI), which are Zn(II)-active and -inactive, respectively. Hybrid quantum mechanics/molecular mechanics calculations were used to obtain geometrical structures of the stationary points along reaction paths, and big quantum mechanical systems with more than 1000 atoms and free-energy perturbations were used to improve the quality of the calculated energies. We studied, on an equal footing, all reasonable reaction paths to the S- and R-enantiomers of HTA from MG and H-SG (the latter was considered in two different binding modes). The results indicate that the MG and H-SG reaction in both enzymes can follow the same path to reach S-HTA. However, the respective overall barriers and reaction energies are different for the two enzymes (6.1 and -9.8 kcal/mol for HuGlxI and 15.7 and -2.2 kcal/mol for ZmGlxI). The first reaction step to produce S-HTA is facilitated by a crystal water molecule that forms hydrogen bonds with a Glu and a Thr residue in the active site. The two enzymes also follow similar paths to R-HTA. However, the reactions reach a deprotonated and protonated R-HTA in the human and corn enzymes, respectively. The production of deprotonated R-HTA in HuGlxI is consistent with other theoretical and experimental works. However, our calculations show a different behavior for ZmGlxI (both S- and R-HTA can be formed in the enzyme with the alcoholic proton on HTA). This implies that Glu-144 of corn GlxI is not basic enough to keep the alcoholic proton. In HuGlxI, the two binding modes of H-SG that lead to S- and R-HTA are degenerate, but the barrier leading to R-HTA is lower than the barrier to S-HTA. On the other hand, ZmGlxI prefers the binding mode, which produces S-HTA; this observation is consistent with experiments. Based on the results, we present a modification for a previously proposed two-substrate reaction mechanism for ZmGlxI.

The metalloenzymes from the alkaline phosphatase (AP) superfamily catalyze the hydrolysis and transphosphorylation of phosphate monoesters. The role of several amino acids highly conserved in the active site of this family of enzymes was examined, using human placental AP (PLAP) as a model protein. By employing an active-site model based on the X-ray crystal structure of PLAP, mutations of several key residues were modeled by quantum mechanical methods in order to determine their impact on the catalytic activity. Kinetic and thermodynamic estimations were achieved for each reaction step of the catalytic mechanism by characterization of the intermediates and transition states on the reaction pathway, and the effects of mutations on the activation barriers were analyzed. A good accordance was observed between the present computational results and experimental measurements reported in the literature.

Esterification of citric acid (CA) with the primary alcohols and the hydroxyl groups of cellulose chain (n = 1-2) in parched condition were investigated by using density functional theory (DFT) method and a two-layer ONIOM approach. Geometry and energy of reactants, products, and transition state (TS) structures were optimized at B3LYP/6-311g (d, p) level and ONIOM (B3LYP/6-311g (d, p):PM3MM) level. The computational results show that the esterification occurs in the two main steps: the first step is the dehydration reaction of CA to form anhydrides of 5-membered ring and 6-membered ring and the second step is the ring opening reaction with the hydroxyl –OH groups to form the ester products. The energy barrier of dehydration reaction step is much higher than that of ring opening reaction step. Effect of substituent R in primary alcohol R-CH2OH (R: CH=CH2, CH2NHCH3, CH2OCH3, CH2Cl) and cellulose chain (1G, 2G) on the reactivity, which has negative inductive effect –I, is significant. The combination of calculation data and experiment data were applied to make findings more rigorous. The activation energy of CA was determined by using differential scanning calorimetry (DSC) and thermal gravimetric (TG) analysis to be E a exp = 47.8 kcal/mol; the experimental data favoured the dehydration reaction step of CA.

Photoconversion of CO2 into fuels completes the carbon neutral cycle in a sustainable society. To exclude the contribution of adventitious carbon, monitoring the time course of 13CO2 conversion into 13C-fuel is essential, but has been rarely reported. In the present work, a composite of Au nanoparticles with ZrO2 was found to be effective in converting 13CO2 into 13CO at a rate of 0.17 μmol h−1 gcat−1 in the presence of H2 and UV–vis light. The detected 12CO as a minor byproduct (11.9 %) was identified as due to adsorbed 12CO2 from the air. The 12C ratio in the total amount of CO2 was evaluated based on a 13CO2 photoexchange reaction (8.7 %). The discrepancy between these values suggested a slower exchange reaction step between the chemisorption site for CO2 reduction and the physisorption site for CO2 compared to the reduction step to CO. Furthermore, based on in-profile kinetic studies using sharp-cut filters and control reactions in the dark, the contribution ratio for CO2 conversion was determined to be via charge separation at the band-gap of ZrO2 (λ 1 2 k T ): 31 %. Localized surface plasmon resonance (LSPR) absorption of Au and infrared absorption in the range of λ > 320 nm did not promote catalysis. The LSPR absorption was further investigated by Au L3-edge extended X-ray absorption fine structure analysis. Ambient heat on the Au nanoparticles should have promoted H2 activation enough, supplying protons to the CO2 reduction sites over ZrO2; however, a temperature increase of 26 K on the Au surface was marginal for further H2 activation. CO2 photoconversion with added moisture was also attempted; the CO formation rate using ZrO2 under these conditions was 0.15 μmol h−1 gcat−1. However, 47 % was characterized as 12CO originating from chemisorbed 12CO2, and H2 was also formed at a comparable rate of 0.14 μmol h−1 gcat−1 from a competing reaction. The addition of Au to ZrO2 was found to suppress CO formation and promote H2 formation, and Mg2+ addition to Au–ZrO2 effectively suppressed H2 formation directing to the CO formation.

The influence of catalyst pretreatment and space velocity in methane decomposition into COx-free hydrogen and carbon nanotubes were investigated over CoMo/MgO catalyst. The reduction of catalyst before methane decomposition leads to a hydrogen production without significant formation of COx (concentration lower than 5 ppm after 25 min of reaction) suitable for its use in fuel cells. However, a high hydrogen space velocity in the pretreatment increased the rate of catalyst deactivation. The CO and CO2 formation rates showed a common trend for all conditions tested: there was a high initial rate and, after 2 min of reaction, there was a lower stabilized rate. The increase in methane space velocity increased the hydrogen formation rate and the degree of carbon nanotubes graphitization. However, it strongly decreases methane conversion, as expected. The use of low hydrogen space velocity, 0.25 h−1, in catalyst pretreatment and high methane space velocity, 8 h−1, in reaction step, provided the highest hydrogen yield and well-structured carbon nanotubes.

We recently reported a general and practical strategy for the Bi(V)-mediated C–H arylation of phenols and naphthols. Our telescoped protocol proceeds via transmetallation from readily available arylboronic acids to a stable Bi(III) precursor, oxidation to a reactive Bi(V) intermediate, and subsequent ortho-selective phenol arylation. The process exhibits broad scope with respect to both components and tolerates functionality that is incompatible with conventional cross-coupling methods. Preliminary investigations provide insight into the mechanism of each key reaction step.1 Introduction2 Design of a Modular and Practical Arylating System3 B-to-Bi Transmetallation: Scope and Mechanism4 Oxidative C–H Arylation: Exemplification and Mechanism5 Conclusionsions

Lignin is abundant in natural world, and it can be converted into value-added chemicals by thermo-chemical method. Since the insufficient understanding of the lignin pyrolysis mechanism limits practical application of lignin pyrolysis, it is quite important to deeply understand the mechanism of lignin pyrolysis from the molecular level. In this work, 1-(4-hydroxy-3-methoxyphenyl)-2-(2-methoxyphenoxy)-1-ethanol was chosen as a β-O-4 type dimer model compound of lignin. Combining the density functional theory (DFT) method with Py-GC/MS to analyze the pyrolysis behavior of lignin dimer model compound, 9 reasonable reaction paths were studied by DFT. The results showed that 2-methoxy-4-vinylphenol (P3) and 2-methoxyphenol (P4) are the main products of lignin dimer model compound pyrolysis. The kinetic and thermodynamics analysis indicates the homolytic cleavage of Cβ–O is the initial reaction step for forming P3 and P4. In the subsequent reactions, P3 is mainly formed by hydrogenation and then dehydration. P4 is mainly formed by hydrogenation. Increasing temperature can promote the spontaneous reaction of the main paths. The exploration for the pyrolysis mechanism of lignin dimer is helpful to directionally regulate lignin pyrolysis products in future studies.

The corn-starch was able to reduce Pd(II) species under relatively low concentration (5.0 wt/vol) leading to the formation of a thermoresponsive palladium nanoparticles-containing hydrogel with D = 16.1 nm ± 6.4 nm. It was successfully applied to the Suzuki–Miyaura reaction step in neat water involved in the synthesis of (±)-N-acetyl-α-methyl-4-biphenylalanine ethyl ester, a direct precursor of an unnatural quaternary biarylalanine.

The hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) is an essential reaction step to produce value-added renewable chemicals and fuels. In this study, it is demonstrated that the disp...

Thermochemical water splitting cycles are recognized as one of the promising pathways for sustainable hydrogen production. In the present study, Iron-chlorine (Fe–Cl) cycle as one of the chlorine family thermochemical cycles where iron chloride is consumed for hydrogen production from water, is considered for a study. This four-step cycle is modelled by Aspen Plus software package and analyzed for performance investigation of each reaction step and system's components. The parametric studies are also performed to assess the effect of operation conditions such as temperature, pressure and steam to feed ratio on the reaction products and conversion rates. Results indicated that although the effect of pressure is not significant on reaction's production rates, an increase in temperature favors oxygen production in reverse deacon reaction and magnetite production in hydrolysis and lowers hydrogen production in the hydrolysis step. On the other hand, steam to chlorine (Cl2) ratio is directly correlated with hydrochloric acid (HCl) and oxygen production in reverse deacon reaction and hydrogen production in hydrolysis.

The generation of reliable experimental data in any experimental scale requires proper procedures not only for the reaction step but also for the feed preparation, separation, and characterization of products as well as calculations of conversion and product yields. Batch reactor is the most used experimental setup for carrying out exploratory studies for catalyst screening and development. This work is focused on describing and discussing a step-by-step methodology for conducting experiments for catalytic hydrotreating of vegetable oils in batch reactor. The proposed methodology considers literature and own experiences on advantages and disadvantages of different feed types, catalysts, experimental setup and procedures, effect of reaction parameters, separation and characterization of products, and calculations.