Complex Reaction Mechanisms Research Articles

Kinetic study on the reaction routes in the oxidation of K/A oil by nitric acid with microreactors

A continuous-flow microreactor system was applied to evaluate the detailed kinetics of the reaction routes involved in the oxidation of K/A oil by nitric acid, which is essential to obtain an in-depth comprehension of complex reaction mechanisms, having important guiding significance for the two-stage temperature control strategy. 6-hydroxyimino-6-nitrohexanoic acid (AMNA) was identified as a major intermediate and its presence was confirmed through UPLC-MS and 1H NMR characterizations. A multi-step reaction kinetic model was developed, revealing good prediction with the experimental results. Finally, the model was applied to investigate the effects of operating parameters on the reaction routes distribution and reaction rate. The simulation results showed that high temperature and nitric acid concentration contributed to high selectivity of adipic acid through promoting the AMNA route, and greatly reduced the required reaction time, indicating that the accurate control over the conditions in this rapid and strongly exothermic process was of paramount importance.

Ezetimibe Prevents IL-1β-induced Inflammatory Reaction in Mouse Chondrocytes via Modulating NF-κB and Nrf2/HO-1 Signaling Crosstalk.

Osteoarthritis is a type of age-related, chronic, and degenerative joint disease. Ezetimibe, a cholesterol absorption inhibitor, is widely used for the treatment of various diseases. However, the role of ezetimibe in osteoarthritis remains unclear. This study aimed to explore the anti-inflammation effect of ezetimibe on mouse chondrocytes. In the present study, ELISA, qPCR and western blot analysis were performed to evaluate the anti-inflammatory effects of ezetimibe. In addition, enzymes that are highly associated with the anabolism and catabolism of the extracellular matrix of the articular cartilage were also evaluated. Treatment with ezetimibe attenuated the IL-1β-induced degradation of the extracellular matrix, including aggrecan and collagen II. Ezetimibe also attenuated the IL-1β-induced expression levels of MMP3, MMP13 and ADAMTS5, thus exerting protective effects against IL-1β- induced extracellular matrix degradation. The complex mechanism of the anti-inflammatory reaction contributed to the activation of the Nrf2/HO-1 pathway and the suppression of the NF-κB pathway. On the whole, the present study demonstrates that ezetimibe may be a promising agent for further osteoarthritis therapy.

A six-lump kinetic model for HDPE/VGO blend hydrocracking

A six lump-based kinetic model has been developed for the hydrocracking of high-density polyethylene (HDPE) blended with vacuum gas oil (VGO) over a PtPd/HY zeolite catalyst. The blend (20 wt% HDPE and 80 wt% VGO) has been hydrocracked in a semi-continuous stirred tank reactor under the following conditions: 400–440 °C; 80 H2 bar; catalyst to feed (C/F) weight ratio, 0.05–0.1 gcat gfeed−1; reaction time, 15–120 min; and stirring rate, 1300 rpm. The kinetic model, which is an approach to tackle the complex reaction mechanism behind the hydrocracking of a HDPE/VGO blend, predicts the evolution over time of product distribution (gas, naphtha, light cycle oil (LCO), heavy cycle oil (HCO), HDPE and coke). The kinetic model and its computed parameters have been used for the simulation of the HDPE/VGO hydrocracking establishing that a C/F ratio of 0.075 gcat gfeed−1 and temperature–time combinations of 430 °C–10 min and 440 °C–70 min are the optimal operating conditions. Under these conditions, a proper balance between the HCO conversion (>80 %), HDPE conversion (>60 %) and liquid fuel production index (>1.0) would be obtained. This kinetic model could serve as a basis for scaling-up in the valorization of waste plastics by co-feeding them to industrial hydrocracking units, within a Waste-Refinery strategy.

Measurements of projectile fragments from 70 Zn (15 MeV/nucleon) + 64 Ni collisions with the MAGNEX spectrometer at INFN-LNS

The present work is focused on our efforts to produce and identify neutron-richrare isotopes from peripheral reactions below the Fermi energy. High-quality experimental data were obtained from a recent experiment with the MAGNEX spectrometer at INFN-LNS in Catania, Italy. The main goal of this effort is to describe the adopted identification techniques used to analyze the data from the reaction 70 Zn (15 MeV/nucleon) + 64 Ni. The particle identification procedure is based on a novel approach that involves the reconstruction of both the atomic number Z and the ionic charge q of the ions, followed by the identification of themass. Our method was successfully applied to identify neutron-rich ejectiles from multinucleon transfer in the above reaction 70 Zn + 64 Ni at 15 MeV/nucleon. The analysis of the data is ongoing. We expect to obtain the angular and momentum distributions of the fragments, along with their production cross sections. These data, along with comparisons with theoretical models are expected to contribute to a better understanding of the complex reaction mechanisms of multinucleon transfer that dominate this energy regime.

A subset-selection-based derivative-free optimization algorithm for dynamic operation optimization in a steel-making process

ABSTRACT Steel-making production is a dynamic process that has the characteristics of high temperature and heat, and a complex reaction mechanism that causes the mechanism model possibly to be unavailable and the system to be a black box. In this article, a dynamic operation optimization (DOO) problem is refined from the basic oxygen furnace (BOF) steel-making process, and the system model is formulated by a data analytics method. This prevents to solve the optimization problem with derivative-based optimization methods. To circumvent these difficulties, a surrogate-model-based derivative-free optimization algorithm is proposed for solving the DOO problem. In order to establish the surrogate model with the least number of function evaluations, a subset selection strategy is designed to find a sparse structure for the optimization problem, based on which a set of simple bases is determined to establish the surrogate model. Moreover, this also reduces the scale of the parameter optimization problem. Numerical experiments on actual production data verify the applicability and effectiveness of the proposed method.

A REVIEW OF RECENT DEVELOPMENT OF THE SOLVENT-DEFICIENT METHOD

The challenges of modern society and the requirements for high-tech materials have led to a new stage in the development of chemical synthesis methods. This stage is demanding a reliable, controllable, and green approach to the production of necessary materials. One of the recently developed approaches for metal oxide nanoparticles synthesis is the solvent deficient method. A cutting edge of this synthetic method is a synthesis with increased control throughout chemical transformation resulting in optimal conditions for materials production. As a result, oxide nanoparticles are produced fast, environmentally friendly, cost-effective, and with low energy consumption. On the other hand, a complex reaction mechanism is presenting a challenge for reliable kinetic studies. The present review follows the recent trends in the development of the solvent deficient method concerning the binary, ternary, and complex metal oxides. Special attention is given to considering approaches responsible for desirable mechanisms of catalytic applications. In future development, the reported synthesis method is expected to be employed in a high entropy oxides formation. Due to simple preparation steps, it will be possible to automatize the reaction procedure and investigate a large number of possible compositions which is imperative for new complex materials. Finally, precursors heating could be transformed from conventional to microwave. Solvent-deficient method deals with precursors sensitive to microwave irradiation which could ensure rapid heating and transformation to desirable oxide nanomaterials.

(Digital Presentation) Oxygen Evolution Reaction in Ru1-XMxO2 (M = Ti, Zr, Nb, Ta, Cr) Doped Catalysts: Activity and Stability Effects

The complex reaction mechanisms and dissolution pathways that drive oxygen evolution reaction on metal and metal oxide surfaces under acidic conditions challenge the development of a highly active, highly stable, and low cost catalyst for proton-exchange membrane (PEM) water electrolyzers. Currently, ruthenium-based materials present lower overpotentials, lower cost and higher global supply compared to iridium-based materials, though they are also considerably less stable. In order to elucidate a way to improve RuO2 stability under the harsh conditions during water electrolysis, we use a density functional theory (DFT) approach to investigate the effects on catalyst structure, OER activity and stability of transition metal substitution within Ru1-xMxO2 (M = Ti, Zr, Nb, Ta, Cr) at different atomic concentrations. Calculations show that M substitution within rutile RuO2 affects the electronic structure resulting in regions of electron accumulation and depletion at the surface and shifts the Ru d-band and O2p band centers, which are highly dependent on dopant characteristics and doped site. Moreover, dissolution calculations on the Ru1-xTixO2 surfaces show that Ti substitution alter the metal dissolution pathway energetics and thermodynamics bringing stability to the catalyst in terms of reducing material loss. Theoretical XRD patterns, Ru d-band and O p-band center calculations, and activation and reaction energy trends are in excellent agreement with experimental results that includes X-ray diffraction analysis, high resolution transmission electron microscopy images, X-ray photoelectron spectroscopy of core and valence bands, and rotating disk electrode measurements. In this presentation, we focus on the theoretical and computational aspects. The evaluation of the thermodynamics and kinetics of the water splitting, and oxygen evolution mechanism is done with spin-polarized plane-wave DFT calculations, while Ab Initio Molecular Dynamics (AIMD) simulations allow following and complementing the understanding of the dynamics of the initial steps of water dissociation on the various M and Ru sites. Electronic structure changes on the surface due to the presence of M before and during the reaction are analyzed based on the density of states and local magnetic moments, and the activation energies are obtained from the climbing Nudge Elastic Band method. Dissolution calculations are carried out with constrained-AIMD simulations using the slow-growth approach within the “Bluemoon ensemble” as implemented in VASP.

Understanding the Transition Process of Cu Oxide to Metallic Under the CO2 Reduction Conditions Probed By Operando Quick-XAS

During the last decades, significant efforts have been made to directly convert CO2 as a potential feedstock into hydrocarbons as fuels and/or basic chemicals for industrial applications. The electrochemical CO2 reduction reaction (CO2RR) is a promising alternative for a large-scale production of hydrocarbons. However, there are still some challenges including poor product selectivity and highly complex multiple-step reaction mechanisms.[1] In order to convert CO2 on a Cu electrode, high overpotentials up to 1.0 V are required, which make the energy efficiency still rather poor and lead to competition with the H2 evolution.[2] Additionally, the morphology of the Cu materials i.e. structure and ‘chemical state’ (metallic vs oxidized, high vs low coordinated) strongly influence the performance of the CO2RR. Recently, we have shown the critical potential of oxide-metal transition processes for Cu oxide foam annealed at 300°C probed by operando XAS, XRD and Raman spectroscopy.[3,4] All three operando techniques showed an entire reduction of Cu oxide to metallic before the production of hydrocarbons starts. [3,4]In this work, we have investigated the kinetics of both electrochemical oxide-metal reduction and CO2RR on nanoporous Cu foams as catalyst precursor annealed at four different temperatures (100°C, 200°C, 300°C, 450°C) in air using operando Quick X-ray Adsorption Spectroscopy (Quick-XAS). The Quick-XAS measurements were carried out in a custom-made spectro-electrochemical flow cell using 0.5 M KHCO3 as the electrolyte, while the XAS-Spectra were measured in transmission mode. The Quick-XANES data was analyzed by linear combination fit (LCF) and principle component analysis (PCA) to monitor the potential dependent changes of the chemical state and coordination number of the Cu species. Based on the Cu K-edge XANES and EXAFS data, we show that the annealing temperature strongly influences the chemical state of the Cu species. More precisely, the population of the Cu(II) species within the as prepared foams increases with increasing annealing temperature. Starting from the different ratios of Cu(0):Cu(I): Cu(II), the oxide-metal transition processes are shifted in the cathodic direction by applying potential steps of 100 mV. With an increase in annealing temperature, this oxide-metal transition is more rapid and occurs at lower cathodic overpotentials, but still before the production of hydrocarbons begins. In contrast, the potential jump experiments of several hundreds of mV lead to different kinetics of the oxide-metal reduction of Cu species. These transition processes and the resulting structure of porous Cu foams have a huge impact on the product distribution for CO2RR. Altogether, our results provide deeper insights into the oxide-metal transition processes to form the catalytically active Cu species for hydrocarbon formation during CO2RR.Reference:[1] S. Nitopi et al., Chemical Reviews, 2019, 119, 7610. [2] C. W. Li et al., Journal of the American Chemical Society, 2012, 134, 7231. [3] A. Dutta et al., Chimia, 2021, 75, 733. [4] A. Dutta et al., Journal of Catalysis, 2020, 389, 592.

The Ongoing Importance of Lithium Primary Batteries: 50+ Years and Going Strong

Lithium anode primary batteries display numerous outstanding characteristics including high energy density, long shelf life, low self-discharge, and ability to function under a broad temperature operating range. This has led to the design and implementation of lithium primary cells for a variety of applications in the commercial, military, space, and medical fields. The development of these primary batteries has required understanding and resolution of complex reaction mechanisms as well as optimized electrode and cell designs to meet the needs of the target applications. Notably, a variety of cathode materials have been paired with lithium metal anodes including carbon monofluoride (CFx), manganese oxide (MnO2), thionyl chloride (SOCl2), and sulfur dioxide (SO2). A specific application of primary lithium battery systems is to power implantable medical devices. These primary systems utilize lithium metal anodes with cathodes such as iodine, manganese oxide, carbon monofluoride, silver vanadium oxide, and hybrid cathodes. While the specific performance requirements of applications vary, lithium batteries can provide the solutions for single use power source needs.

Perovskite-based electrocatalysts for oxygen evolution reaction in alkaline media: A mini review.

Water electrolysis is one of the attractive technologies for producing clean and sustainable hydrogen fuels with high purity. Among the various kinds of water electrolysis systems, anion exchange membrane water electrolysis has received much attention by combining the advantages of alkaline water electrolysis and proton exchange membrane water electrolysis. However, the sluggish kinetics of the oxygen evolution reaction, which is based on multiple and complex reaction mechanisms, is regarded as a major obstacle for the development of high-efficiency water electrolysis. Therefore, the development of high-performance oxygen evolution reaction electrocatalysts is a prerequisite for the commercialization and wide application of water electrolysis systems. This mini review highlights the current progress of representative oxygen evolution reaction electrocatalysts that are based on a perovskite structure in alkaline media. We first summarize the research status of various kinds of perovskite-based oxygen evolution reaction electrocatalysts, reaction mechanisms and activity descriptors. Finally, the challenges facing the development of perovskite-based oxygen evolution reaction electrocatalysts and a perspective on their future are discussed.

Optimized NiFe-Based Coordination Polymer Catalysts: Sulfur-Tuning and Operando Monitoring of Water Oxidation.

In-depth insights into the structure-activity relationships and complex reaction mechanisms of oxygen evolution reaction (OER) electrocatalysts are indispensable to efficiently generate clean hydrogen through water electrolysis. We introduce a convenient and effective sulfur heteroatom tuning strategy to optimize the performance of active Ni and Fe centers embedded into coordination polymer (CP) catalysts. Operando monitoring then provided the mechanistic understanding as to how exactly our facile sulfur engineering of Ni/Fe-CPs optimizes the local electronic structure of their active centers to facilitate dioxygen formation. The high OER activity of our optimized S-R-NiFe-CPs outperforms the most recent NiFe-based OER electrocatalysts. Specifically, we start from oxygen-deprived Od-R-NiFe-CPs and transform them into highly active Ni/Fe-CPs with tailored sulfur coordination environments and anionic deficiencies. Our operando X-ray absorption spectroscopy analyses reveal that sulfur introduction into our designed S-R-NiFe-CPs facilitates the formation of crucial highly oxidized Ni4+ and Fe4+ species, which generate oxygen-bridged NiIV-O-FeIV moieties that act as the true OER active intermediates. The advantage of our sulfur-doping strategy for enhanced OER is evident from comparison with sulfur-free Od-R-NiFe-CPs, where the formation of essential high-valent OER intermediates is hindered. Moreover, we propose a dual-site mechanism pathway, which is backed up with a combination of pH-dependent performance data and DFT calculations. Computational results support the benefits of sulfur modulation, where a lower energy barrier enables O-O bond formation atop the S-NiIV-O-FeIV-O moieties. Our convenient anionic tuning strategy facilitates the formation of active oxygen-bridged metal motifs and can thus promote the design of flexible and low-cost OER electrocatalysts.

A mechanistic approach to the electrografting of carbon surfaces and electrochemical properties of the grafted films – A critical review

Modification of carbon surfaces by electrografting is a relevant topic due to its potential applications in different fields of science, which has motivated the publication of many works focused on different methodologies to get covalently attached films or to study their properties. Diverse organic molecules have been found to be able to produce grafted films on carbon-based electrodes and their reduction or oxidation involve free radicals that participate in complex reaction mechanisms, from the incipient radical attack of the electrode surface until the film growth. Once the grafted film is generated, electron conduction as well as mass transport through this film are processes that depend on many experimental factors, which are still susceptible of further studies. Hence, the knowledge of the grafting mechanisms is always useful for designing grafted films with more specific and controlled properties. Therefore, this critical review is focused to the main mechanistic aspects of different electrochemical methodologies to get grafted films on carbon surfaces. The use of cyclic voltammetry as tool of modification and characterization of electrochemically active films is summarized. Information about the use of reversible redox probes as indirect method to infer structural information of grafted films is also discussed. Structural reorganization, permeation processes, supporting electrolyte effects and rectification of voltametric responses of redox probes on grafted electrodes were also considered.

Electrochemical performance of high and medium entropy oxides for lithium batteries

Various high and medium entropy oxides with rock salt structures were prepared and studied as anodes for lithium batteries. All the systems had complex reaction mechanisms involving conversion reactions. Their capacity and reduction potential depend on the number of components and microstructure of the initial materials. However, the dependence is difficult to rationalize based on simple stability logic. This paper discusses the implication of our findings in the wider context of the science of high entropy materials.

Discovery of Complex Binding and Reaction Mechanisms from Ternary Gases in Rare Earth Metal-Organic Frameworks.

Understanding the selectivity of metal-organic frameworks (MOFs) to complex acid gas streams will enable their use in industrial applications. Herein, ab initio molecular dynamic simulations (AIMD) were used to simulate ternary gas mixtures (H2 O-NO2 -SO2 )in rare earth 2,5-dihydroxyterephthalic acid (RE-DOBDC) MOFs. Stronger H2 O gas-metal binding arose from thermal vibrations in the MOF sterically hindering access of SO2 and NO2 molecules to the metal sites. Gas-gas and gas-linker interactions within the MOF framework resulted in the formation of multiple secondary gas species including HONO, HNO2 , NOSO, and HNO3 - . Four gas adsorption sites were identified along with a new de-protonation reaction mechanism not observable through experiment. This study not only provides valuable information on competitive gas binding energies in the MOF, it also provides important chemical insights into transient chemical reactions and mechanisms.

A review on bio-crude production from algal biomass using catalytic hydrothermal liquefaction process

The rising demand for cleaner energy among the nations has turned the focus from fossil fuel-based energy sources to renewables like biomass, solar, wind, etc. Biomass conversion to fuel has increased research in recent times due to its ease and availability throughout the year. Hydrothermal liquefaction is the process where biomass converts to a liquid product via complex reaction mechanisms. This review aims to summarize the hydrothermal liquefaction of algal biomass and the improvements in the bio-crude yield using heterogeneous and homogenous catalysts. Many references have been reviewed to provide the sources for the process and have been critically well structured. This review also provided information regarding the reaction pathway for algal biomass and the effects of process parameters like temperature, residence time, pH, etc. The focus of the review is on the effects of various catalysts based on their dosage whose results collected from various sources have been tabulated. The review briefly discusses the applications of products formed during hydrothermal liquefaction after post-processing.

Recent progress of electrochemical reduction of CO2 by single atom catalysts

Powered by electricity from renewable energies, electrochemical reduction of CO2 could not only efficiently alleviate the excess emission of CO2, but also produce many kinds of valuable chemical feedstocks. Among various catalysts, single atom catalysts (SACs) have attracted much attention due to their high atom utilization efficiency and expressive catalytic performances. Additionally, SACs serve as an ideal platform for the investigation of complex reaction pathways and mechanisms thanks to their explicit active sites. In this review, the possible reaction pathways for the generation of various products (mainly C1 products for SACs) were firstly summarized. Then, recent progress of SACs for electrochemical reduction of CO2 was discussed in aspect of different central metal sites. As the most popular and efficient coordination modulation strategy, introducing heteroatom was then reviewed. Moreover, as an extension of SACs, the development of dual atom catalysts was also briefly discussed. At last, some issues and challenges regarding the SACs for CO2 reduction reaction (CO2RR) were listed, followed by corresponding suggestions.

Pathogenic bacteria remodel central metabolic enzyme to build a cyclopropanol warhead

Bacteria of the Burkholderia pseudomallei (BP) group pose a global health threat, causing the infectious diseases melioidosis, a common cause of pneumonia and sepsis, and glanders, a contagious zoonosis. A trait of BP bacteria is a conserved gene cluster coding for the biosynthesis of polyketides (malleicyprols) with a reactive cyclopropanol unit that is critical for virulence. Enzymes building this warhead represent ideal targets for antivirulence strategies but the biochemical basis of cyclopropanol formation is unknown. Here we describe the formation of the malleicyprol warhead. We show that BurG, an unusual NAD+-dependent member of the ketol-acid reductoisomerase family, constructs the strained cyclopropanol ring. Biochemical assays and a suite of eight crystal structures of native and mutated BurG with bound analogues and inhibitors provide snapshots of each step of the complex reaction mechanism, involving a concealed oxidoreduction and a C–S bond cleavage. Our findings illustrate a remarkable case of neofunctionalisation, where a biocatalyst from central metabolism has been evolutionarily repurposed for warhead production in pathogens.

Challenges and advances of organic electrode materials for sustainable secondary batteries.

Organic electrode materials (OEMs) emerge as one of the most promising candidates for the next-generation rechargeable batteries, mainly owing to their advantages of bountiful resources, high theoretical capacity, structural designability, and sustainability. However, OEMs usually suffer from poor electronic conductivity and unsatisfied stability in common organic electrolytes, ultimately leading to their deteriorating output capacity and inferior rate capability. Making clear of the issues from microscale to macroscale level is of great importance for the exploration of novel OEMs. Herein, the challenges and advanced strategies to boost the electrochemical performance of redox-active OEMs for sustainable secondary batteries are systematically summarized. Particularly, the characterization technologies and computational methods to elucidate the complex redox reaction mechanisms and confirm the organic radical intermediates of OEMs have been introduced. Moreover, the structural design of OEMs-based full cells and the outlook for OEMs are further presented. This review will shed light on the in-depth understanding and development of OEMs for sustainable secondary batteries.

Two routes to hydrogen evolution for a Co-polypyridyl complex with two open sites

Cobalt polypyridyl complexes efficiently catalyze hydrogen evolution in aqueous media and exhibit high stability under reducing conditions. Their stability and activity can be tuned through electronic and steric considerations, but the rationalization of these effects requires detailed mechanistic understanding. As an example, tetradentate ligands with two non-permanently occupied coordination sites show higher activity with these sites in cis compared to trans configuration. Here reaction mechanisms of the Co-polypyridyl complex [CoII(bpma)Cl2] (bpma = bipyridinylmethyl-pyridinylmethyl-methyl-amine) have been studied using hybrid density-functional theory. This complex has two exchangeable cis sites, and provides a flexible ligand environment with both pyridyl and amine coordination. Two main pathways with low barriers are found. One pathway, which includes both open sites, is hydrogen evolution from a CoII-H intermediate with a water ligand as the proton donor. In the second pathway H–H bond formation occurs between the hydride and the protonated bpma ligand, with one open site acting as a spectator. The two pathways have similar barriers at higher pH, while the latter becomes more dominant at lower pH. The calculations consider a large number of interconnected variables; protonation sites, isomers, spin multiplicities, and the identities of the open binding sites, as well as their combinations, thus exploring many simultaneous dimensions within each pathway. The results highlight the effects of having two open cis-coordination sites and how their relative binding affinities change during the reaction pathway. They also illustrate why CoII-H intermediates are more active than CoIII-H ones, and why pyridyl protonation gives lower reaction barriers than amine protonation.

Predicting binding motifs of complex adsorbates using machine learning with a physics-inspired graph representation.

Computational screening in heterogeneous catalysis relies increasingly on machine learning models for predicting key input parameters due to the high cost of computing these directly using first-principles methods. This becomes especially relevant when considering complex materials spaces such as alloys, or complex reaction mechanisms with adsorbates that may exhibit bi- or higher-dentate adsorption motifs. Here we present a data-efficient approach to the prediction of binding motifs and associated adsorption enthalpies of complex adsorbates at transition metals and their alloys based on a customized Wasserstein Weisfeiler-Lehman graph kernel and Gaussian process regression. The model shows good predictive performance, not only for the elemental transition metals on which it was trained, but also for an alloy based on these transition metals. Furthermore, incorporation of minimal new training data allows for predicting an out-of-domain transition metal. We believe the model may be useful in active learning approaches, for which we present an ensemble uncertainty estimation approach.