Reaction Pathways Research Articles

Catalytic performance of low loading palladium-carbon catalyst in rosin disproportionation: Characterization, process enhancement, and reaction pathway

Catalytic performance of low loading palladium-carbon catalyst in rosin disproportionation: Characterization, process enhancement, and reaction pathway

Understanding key interactions between NOx and C2-C5 alkanes and alkenes: The ab initio kinetics and influences of H-atom abstractions by NO2

This study aims to reveal the important role and the respective rate rules of H-atom abstractions by NO2 for better understanding NOX/hydrocarbon interactions. To this end, H-atom abstractions from C2-C5 alkanes and alkenes (15 species) by NO2, leading to the formation of three HNO2 isomers (trans-HONO, HNO2, and cis-HONO) and their respective products (45 reactions), are first characterized through quantum chemistry computation, where electronic structures, single point energies, C-H bond dissociation energies and 1-D hindered rotor potentials are determined at DLPNO-CCSD(T)/cc-pVDZ//M06–2X/6−311++g(d,p). The rate coefficients for all studied reactions, over a temperature range from 298.15 to 2000 K, are computed using transition state theory with the Master Equation System Solver program. Comprehensive analysis of branching ratios elucidates the diversity and similarities between different species, HNO2 isomers, and abstraction sites, from which accurate rate rules are determined. With the rate rules, the rate coefficients at various reaction sites on heavier hydrocarbons (e.g., > C5) can be reliably estimated by analogy. Incorporating the updated rate parameters into a detailed chemical kinetic model reveals the significant influences of this type of reaction on model prediction results, where the simulated ignition delay times are either prolonged or reduced, depending on the original rate parameters presented in the selected model. Sensitivity and flux analysis further highlight the critical role of this type of reaction in affecting system reactivity and reaction pathways, emphasizing the need for adequately representing these kinetics in existing chemistry models. This can now be sufficiently achieved for alkanes and alkenes based on the results from this study.

Innovative formaldehyde adsorption with optimized deep eutectic solvents: An experiment and multilevel computational chemistry approach.

Formaldehyde, a hazardous gas that is exposed to everyone every day, has been proven to pose an elevated risk of respiratory problems, allergies, and chronic diseases. Adsorption technologies have proven to be a straightforward and labor-saving method to reduce indoor formaldehyde levels. Currently, extensive research has been conducted utilizing Deep Eutectic Solvents (DES) as adsorbents for harmful gases, yet the adsorption and conversion mechanisms for formaldehyde remain unclear. In this study, we highlighted the adsorption and transformation mechanisms of formaldehyde with DES employing quantum chemical and molecular dynamics calculations. Initially, thermodynamic software (CosmoTherm) was employed to calculate the logarithmic activity coefficients (LAC) of formaldehyde and determine the solid-liquid equilibrium (SLE) for 416 combinations of DES. On the basis of the eutectic point and LAC of DES, potential formaldehyde adsorbents were screened. In the second step, the DES screened out has a good formaldehyde adsorption capacity through the experiment. Finally, the reactive sites, reaction pathways, van der Waals interactions, and hydrogen bonds of DES of L-cysteine/diethanolamine (CYS-DEA) and formaldehyde were studied through a theoretical approach. This study comprehensively elucidates the screening of formaldehyde adsorbents, experimental adsorption, and adsorption mechanisms. Significantly shortens the development cycle of DES as formaldehyde adsorbents.

Intra/extracellular transmembrane electron transfer for bioelectric enhancement mediated by in-situ bio-FeS and polypyrrole coating

This study involves the construction of an “inside-out” electronic network channel with in-situ formation of biogenic FeS (bio-FeS) nanoparticles in cells of Shewanella oneidensis MR-1 (S. oneidensis MR-1) and a coating of conductive polypyrrole (PPy) on the outer surface of entire cells. The microbial fuel cell driven by bio-FeS and PPy co-modified S. oneidensis MR-1 (FeS/PPy@MR-1) has a maximum power density 3.6 times higher than that of the native strain. Electrochemical analysis demonstrates that the modifications of bio-FeS and PPy markedly enhance the direct electron transfer and c-type cytochrome-bound flavin-mediated single-electron reaction pathways and expand the electron output flux. The electron-donating ability of FeS/PPy@MR-1 is 7 times greater than that of the native strain. Bio-FeS and PPy can mediate novel intra/extracellular transmembrane electron transport pathways independent of the traditional respiratory chain, bridge spatially discrete redox environments, and optimize electron transfer pathways to intracellular to extracellular transfer electrons rapidly and maximally. These findings provide insights into conductive nanomaterial-mediated intra/extracellular transmembrane electron transfer, which is critical for the environment and bioenergy fields.

Transesterification of glycerol with dimethyl carbonate for the synthesis of glycerol carbonate and glycidol by Iron (III) salen complex

The transesterification of glycerol and dimethyl carbonate (DMC) was investigated in the presence of μ-oxo-Fe(salen)2 under the optimal reaction condition. Several transition metal(salen) were tested, and only Fe (salen) shows an excellent results towards transesterification of glycerol. Therefore, Fe (salen) was characterized by IR, elemental analysis, MS, XPS and Surface Basicity test, and it can be confirmed that the as-synthesized Fe(salen) was existed in the form of μ-oxo-Fe(salen)2. It was proposed that the μ-oxo-Fe(salen)2 can provide two different reaction pathway based on its molecular structures and the electronic configuration of iron itself. μ-oxo-Fe(salen)2 was reacted with the mixture of glycerol and DMC under microwave-heating in 60 min at 100°C and at the molar ratio of glycerol:DMC:μ-oxo-Fe(salen)2 of 1:2:0.01 and obtaining the highest glycerol carbonate yield of 93.8 %.

Key reaction pathways for NO reduction by NH3 in the reduction zone during ammonia-coal co-firing: A combined experimental and DFT study

Key reaction pathways for NO reduction by NH3 in the reduction zone during ammonia-coal co-firing: A combined experimental and DFT study

Investigation of NO emission characteristics from co-combustion of methane and ammonia at high-altitude areas

The high-altitude areas of China are abundant in renewable energy and have a natural advantage in ammonia production. Based on this advantage, this paper proposes a co-combustion strategy for methane and ammonia to reduce carbon emissions in these areas. However, the NO emission characteristics associated with this strategy remain uncertain. A custom-designed combustion system capable of simulating high-altitude environments was used to investigate the effect of ammonia mixing ratio, equivalence ratio, and pressure on NO emission in methane/ammonia/air flames. Additionally, chemical kinetic calculations were conducted to explore the mechanisms of how sub-atmospheric pressure influences NO emission. The results indicate that for stoichiometric flames, NO increases with the ammonia mixing ratio. In fuel-rich flames, NO remains nearly constant once the ammonia mixing ratio exceeds 10%. Sub-atmospheric pressure leads to higher NO, particularly in fuel-rich flames, where the increase can reach up to 24.4%. Analysis of nitrogen reaction pathways and key radical concentrations reveals that sub-atmospheric pressure has a minimal effect on nitrogen conversion pathways. The variation in NO is achieved by altering the pathway contributions and the concentrations of H, NH, and N. This work provides direction and guidance for improving the application of methane and ammonia co-combustion in high-altitude areas.

PH-Controlled DNA Switching Circuits with Multi-State Responsiveness for Logic Computation and Control.

Dynamic control of DNA circuit functionality is essential for constructing chemical reaction networks (CRNs) that implement complex functions. The triplex has been utilized for dynamically regulating the diverse functionalities of DNA circuits due to its distinctive pH responsiveness. However, it is challenging for triplexes to independently regulate the functionality of DNA circuits, as various triplexes were often required for DNA circuits to function in complex environments, which adds complexity to the design and control of dynamic circuits. Here, we proposed a pH-controlled multi-state DNA switching circuit construction strategy to realize dynamic regulation among three states through conformational transitions of the triplex. In addition, by leveraging the regulatory role of multi-state DNA switching circuits on the toehold-mediated strand displacement reaction, we constructed switchable DNA circuits for logic computation and control of hybridization chain reaction (HCR). We confirmed that the designed DNA switching circuits exhibited multi-state responsiveness, allowing for different logical operations at varying pH levels and programmable control of the diverse reaction pathways in the HCR. Our strategy offers a convenient approach for the intelligent response and dynamic regulation of large-scale CRNs and DNA nanostructure self-assembly. It promises applications in biosensing, disease detection and drug delivery.

Manipulating the interfacial integration mode of a bio-templated porous ZSM-5 platform with an Au/CuZnOx catalyst for enhanced efficiency and recycling stability in glycerol conversion to 1,3-dihydroxyacetone.

Despite the potential to significantly enhance the economic viability of biomass-based platforms through the selective conversion of glycerol to 1,3-dihydroxyacetone (DHA), a formidable challenge persists in simultaneously achieving high catalytic activity and stability along this reaction pathway. Herein, we have devised a strategic approach to manipulate the interfacial integration within composite catalysts to address the performance trade-off. Through the modulation of the composite process involving a bio-templated porous ZSM-5 zeolite platform (bZ) and an Au/CuZnOx catalyst, three distinct interfacial bonding modes were achieved: physical milling, encapsulation by zeolite, and in situ growth on zeolite. The catalyst prepared via the physical milling mode (denoted as Au/CuZnOx@bZ) demonstrated remarkable catalytic efficiency with a glycerol conversion rate of 93% and a DHA selectivity of 86%. In particular, Au/CuZnOx@bZ maintained over 72% of glycerol conversion and DHA selectivity even after five cycles, exhibiting superior stability that surpasses the majority of current catalysts. The differences in interfacial integration modes play a crucial role in regulating the surface Au+ content and the reduction temperatures of the catalysts and minimizing Au nanoparticle agglomeration during cycling, as confirmed by comprehensive characterization and experimental analyses.

Mechanistic Insights into the Aerobic Oxidation of 2,5-Bis(hydroxymethyl)furfural to 2,5-Furandicarboxylic Acid on Pd Catalysts.

2,5-Furandicarboxylic acid (FDCA) is one of the top selected value-added chemicals, which can be obtained by the aerobic oxidation of 2,5-bis(hydroxymethyl)furfural (BHMF) over a Pd-based catalyst. However, the elucidation of the reaction mechanism was hindered by its rapid kinetics. Herein, employing the density functional theory (DFT) calculations, we delve into the detailed reaction pathways of the BHMF oxidation into FDCA over Pd(111) and PdHx(111) identifying the rate-determining steps. The results demonstrated that 2,5-diformylfuran (DFF) and 5-formyl-2-furancarboxylic acid (FFCA) are the important intermediates, while the oxidation of FFCA is the rate-limiting step with the energy barrier of 0.68 and 0.51 eV on Pd(111) and PdH1/4(111), respectively. By comparison of the d-band center of Pd(111) and PdHx(111) surfaces and the overall energy barrier of this reaction over these two surfaces, it makes clear that the occupation of H atoms in the Pd bulk changes the surface electronic structures and enhances the binding energy of BHMF with the PdHx surface, which consequently speeds up the conversion of BHMF into FDCA. Water plays a crucial role in facilitating the activation of O2 via the H-transfer by constructing a hydrogen-bonding chain with the O2 and OH*. The activation of molecular oxygen experiences enhancement through the synergy of OH* and H2O, resulting in the production of actomic oxygen (O*). Both O* and OH* actively participate in the BHMF oxidation, where O* improved the activation toward initial critical reaction pathways on Pd(111) while OH* exhibited its pronounced impact on the latter two key processes on both Pd(111) and PdH1/4(111). This study will contribute to well understanding the oxidation mechanism of BHMF into FDCA over Pd-based catalysts and establish a theoretical framework for the potential development of an effective catalyst.

Chemically Triggered Reactive Coacervates Show Life-Like Budding and Membrane Formation.

Phase-separated coacervates can enhance reaction kinetics and guide multilevel self-assembly, mimicking early cellular evolution. In this work, we introduce "reactive" complex coacervates that undergo chemically triggered self-immolative transformations, directing the self-assembly of the reaction products within their matrix. These self-assemblies then evolve to show life-like properties such as budding and membrane formation. We find that the coacervate composition critically influences reaction rates and product distribution and guides the hierarchical self-assembly. This work showcases "reactive" coacervates as a versatile platform to influence reaction and self-assembly pathways for controlled supramolecular synthesis and hierarchical self-organization in confined spaces.

Density Functional Theory Study on Reconstruction and Reversible Transformation Processes of the ZZ57 Edge Structure in Carbon Materials: Effect of Na, K, and Ca.

The edge structures of carbonaceous materials exhibit temperature-dependent behavior on the atomic scale, with variations in the relative ratios of zigzag, reconstructed 5-7 zigzag (ZZ57), and armchair edges observed at different temperatures. Nevertheless, the mechanisms underlying the interconversion of these edge structures and the influence of the surrounding metals remain unclear. This study investigates the reconstruction and reversible transformation processes of ZZ57 edge structures in carbon materials and examines the effects of different metal atoms (Na, K, and Ca) by using density functional theory. The simplified Z57 and A57 models are selected to simulate the microscopic reaction pathways at the isolated system level. Wave function analysis is conducted to determine the physical and chemical characteristics of ZZ57 edge structures and to predict the optimal adsorption positions of the metal atoms. Results indicate that the ZZ57 edge structure reconstruction and reversible transformation are exothermic reactions that proceed favorably in the forward direction. Analysis of the ten-membered ring in the transition state structure shows that the average bond order of the C-C bond is lower than that in the benzene ring system. Thermodynamic analysis shows that Na, K, and Ca atoms reduce the chemical equilibrium constant, thereby hindering the progress of the reactions. These findings not only provide specific theoretical insights into the transformation of the ZZ57 edge structure but also offer guidance for the precise design of carbon edges and the development of practical carbon materials.

Transforming Adsorbate Surface Dynamics in Aqueous Electrocatalysis: Pathways to Unconstrained Performance.

Developing highly efficient catalysts to accelerate sluggish electrode reactions is critical for the deployment of sustainable aqueous electrochemical technologies, yet remains a great challenge. Rationally integrating functional components to tailor surface adsorption behaviors and adsorbate dynamics would divert reaction pathways and alleviate energy barriers, eliminating conventional thermodynamic constraints and ultimately optimizing energy flow within electrochemical systems. This approach has, therefore, garnered significant interest, presenting substantial potential for developing highly efficient catalysts that simultaneously enhance activity, selectivity, and stability. The immense promise and rapid evolution of this design strategy, however, do not overshadow the substantial challenges and ambiguities that persist, impeding the realization of significant breakthroughs in electrocatalyst development. This review explores the latest insights into the principles guiding the design of catalytic surfaces that enable favorable adsorbate dynamics within the contexts of hydrogen and oxygen electrochemistry. Innovative approaches for tailoring adsorbate-surface interactions are discussed, delving into underlying principles that govern these dynamics. Additionally, perspectives on the prevailing challenges are presented and future research directions are proposed. By evaluating the core principles and identifying critical research gaps, this review seeks to inspire rational electrocatalyst design, the discovery of novel reaction mechanisms and concepts, and ultimately, advance the large-scale implementation of electroconversion technologies.

Rational Design Two- or Four-Electron Reaction Pathway Covalent Organic Frameworks for Efficient and Selective Electrocatalytic Hydrogen Peroxide Production.

Covalent organic frameworks (COFs) are often employed in oxygen reduction reactions (ORR) for hydrogen peroxide production due to their tunable structures and compositions. However, COF electrocatalysts require precise structural engineering, such as heteroatoms or metal site doping, to modulate the reaction pathway during the ORR process. In this work, we designed a tetraphenyl-p-phenylenediamine based COF electrocatalyst, namely TPDA-BDA, which exhibited excellent two-electron (2e) ORR performance with high H2O2 selectivity of 89.7% and faraday efficiency (FE) of 86.7%, higher than the reported COFs to date for H2O2 electrosynthesis. The theoretical and experimental results showed that the rate-determining step energy barrier for reduction of O2 to OOH* intermediates was significantly reduced by replacing of bipyridine with biphenyl blocks, changing from 4e to 2e ORR reaction pathway. Also, the donor-acceptor characteristic and narrower optical band gap of TPDA-BDA COF enhanced the electronic conductivity and reduction ability, thus elevating the catalytic activity. As a result, the H2O2 selectivity was maintained above 85% even after 50 h stability test. This work reveals the structure-property relationship of COF electrocatalysts and provides a new strategy for rational design of high performance 2e ORR COF electrocatalysts for efficient and selective hydrogen peroxide production.

Recent Progress of Chemical Reactions Induced by Contact Electrification

Contact electrification (CE) spans from atomic to macroscopic scales, facilitating charge transfer between materials upon contact. This interfacial charge exchange, occurring in solid–solid (S–S) or solid–liquid (S–L) systems, initiates radical generation and chemical reactions, collectively termed contact-electro-chemistry (CE-Chemistry). As an emerging platform for green chemistry, CE-Chemistry facilitates redox, luminescent, synthetic, and catalytic reactions without the need for external power sources as in traditional electrochemistry with noble metal catalysts, significantly reducing energy consumption and environmental impact. Despite its broad applicability, the mechanistic understanding of CE-Chemistry remains incomplete. In S–S systems, CE-Chemistry is primarily driven by surface charges, whether electrons, ions, or radicals, on charged solid interfaces. However, a comprehensive theoretical framework is yet to be established. While S–S CE offers a promising platform for exploring the interplay between chemical reactions and triboelectric charge via surface charge modulation, it faces significant challenges in achieving scalability and optimizing chemical efficiency. In contrast, S–L CE-Chemistry focuses on interfacial electron transfer as a critical step in radical generation and subsequent reactions. This approach is notably versatile, enabling bulk-phase reactions in solutions and offering the flexibility to choose various solvents and/or dielectrics to optimize reaction pathways, such as the degradation of organic pollutants and polymerization, etc. The formation of an interfacial electrical double layer (EDL), driven by surface ion adsorption following electron transfer, plays a pivotal role in CE-Chemical processes within aqueous S–L systems. However, the EDL can exert a screening effect on further electron transfer, thereby inhibiting reaction progress. A comprehensive understanding and optimization of charge transfer mechanisms are pivotal for elucidating reaction pathways and enabling precise control over CE-Chemical processes. As the foundation of CE-Chemistry, charge transfer underpins the development of energy-efficient and environmentally sustainable methodologies, holding transformative potential for advancing green innovation. This review consolidates recent advancements, systematically classifying progress based on interfacial configurations in S–S and S–L systems and the underlying charge transfer dynamics. To unlock the full potential of CE-Chemistry, future research should prioritize the strategic tuning of material electronegativity, the engineering of sophisticated surface architectures, and the enhancement of charge transport mechanisms, paving the way for sustainable chemical innovations.

Unconventional and Powerful Ion Sources for Solid-State Ion Exchange, Cu2SO4 and Cu3PO4: Exemplified by the Synthesis of Metastable β-CuGaO2 from Stable β-LiGaO2.

This study introduces a new method for synthesizing Cu+-containing metastable phases through ion exchange. Traditionally, CuCl has been used as a Cu+ ion source for solid-state ion exchanges; however, its thermodynamic driving force is often insufficient for complete ion exchange with Li+-containing precursors. First-principles calculations have identified Cu2SO4 and Cu3PO4 as more powerful alternatives, providing a higher driving force than CuCl. It has been experimentally demonstrated that these ion sources can open up new reaction pathways through experimental ion exchanges, such as from β-LiGaO2 to β-CuGaO2, which were previously unattainable. An important perspective provided by this study is that the potential of such simple compounds to act as powerful ion sources has been overlooked and that they were identified through straightforward first-principles calculations. This work presents the initial strategic design of an ion-exchange reaction by exploring suitable ion sources, thereby expanding the potential for synthesizing metastable materials.

Rational Design Two‐ or Four‐Electron Reaction Pathway Covalent Organic Frameworks for Efficient and Selective Electrocatalytic Hydrogen Peroxide Production

Covalent organic frameworks (COFs) are often employed in oxygen reduction reactions (ORR) for hydrogen peroxide production due to their tunable structures and compositions. However, COF electrocatalysts require precise structural engineering, such as heteroatoms or metal site doping, to modulate the reaction pathway during the ORR process. In this work, we designed a tetraphenyl‐p‐phenylenediamine based COF electrocatalyst, namely TPDA‐BDA, which exhibited excellent two‐electron (2e) ORR performance with high H2O2 selectivity of 89.7% and faraday efficiency (FE) of 86.7%, higher than the reported COFs to date for H2O2 electrosynthesis. The theoretical and experimental results showed that the rate‐determining step energy barrier for reduction of O2 to OOH* intermediates was significantly reduced by replacing of bipyridine with biphenyl blocks, changing from 4e to 2e ORR reaction pathway. Also, the donor‐acceptor characteristic and narrower optical band gap of TPDA‐BDA COF enhanced the electronic conductivity and reduction ability, thus elevating the catalytic activity. As a result, the H2O2 selectivity was maintained above 85% even after 50 h stability test. This work reveals the structure‐property relationship of COF electrocatalysts and provides a new strategy for rational design of high performance 2e ORR COF electrocatalysts for efficient and selective hydrogen peroxide production.

Formal Transesterification Reaction of But-3-enyl Esters Enabled by a Synergistic Nickel/Zinc Relay.

The transition metal-catalyzed coupling reaction has renewed the role of ester as an electrophilic partner. In this context, we describe a synergistic Ni/Zn-catalyzed formal transesterification reaction of but-3-enyl esters with tetrahydrofuran and alkyl iodides to give 4-alkoxylbutyl esters. The aromatic and aliphatic esters are both competent electrophiles and thus broaden the substrate scope of esters in coupling reactions, because the electrophiles in previously reported work were strictly limited to aromatic ones. Mechanistic studies reveal that the C(acyl)-O bond or even more inert C(alkyl)-O bond of esters could be cleaved under nickel catalysis. Two catalytic cycles are proposed, which represent a new reaction pathway versus the traditional transesterification.

Effect of Water in Coal Matrix on the Physicochemical Adsorption Process During Low-Temperature Oxidation of Coal

ABSTRACT This study investigates the impact of water on oxygen adsorption in coal using quantum simulations, focusing on three typical oxygen-containing functional groups in lignite. Key factors, including equilibrium configurations, electrostatic potential, and reduced density gradients of water and oxygen molecules adsorbed on the coal surface, were analyzed. Thermal analysis and quantum chemical calculations were also performed to determine enthalpy changes and activation energies in oxidation reactions. The results indicate that water influences oxygen adsorption on coal surfaces through both physical and chemical mechanisms. Physically, water molecules form hydrogen bonds with the oxygen-containing groups in coal, altering the electronic density distribution and enhancing oxygen adsorption. Chemically, water reduces activation energy, modifies reaction barriers, and facilitates spontaneous combustion at lower temperatures, while also increasing enthalpy changes of oxidation reactions. Overall, water plays a dual role in regulating coal oxidation: it enhances adsorption through hydrogen bonding while also altering reaction pathways and lowering energy barriers, thereby promoting coal oxidation.

Photoelectrocatalyzed Alkylation of Phosphonites by Direct Decarboxylative C(sp3)-P Coupling.

A photoelectrocatalytic method is presented that achieves direct decarboxylative C(sp3)-P coupling, providing a modular route to alkylphosphinates and alkylphosphonates from readily available carboxylic acids. The success of this reaction hinges on the synergistic combination of electrochemical anodic oxidation and photocatalytic ligand to metal charge transfer (LMCT) decarboxylation. By employing P(III) reagents as limiting reagents, our approach enables efficient alkyl modification of medicinally important nucleosides and complex molecules derived phosphonites, which were challenging to access by existing methods. Detailed mechanistic studies elucidate the critical roles of Fe catalysts and additives, offering valuable insights into the reaction pathway and laying the foundation for future advancements in photoelectrocatalytic C(sp3)-heteroatom bond-forming reactions.