Activation Barrier Of Reaction Research Articles

Preferred Electric Field Mechanism for Frustrated Lewis Pair Reactivity.

This study employs computational methods to investigate the mechanism of H2 activation by frustrated Lewis pair (FLP) species, including both intermolecular and intramolecular nitrothane/borane FLP systems. Previous studies have proposed two qualitative reactivity mechanism models to explain the facile cleavage of H2 by FLPs. The findings of this study support the electric field mechanism as the favorable pathway for H2 cleavage. Utilizing frontier molecular orbital theory and energy decomposition analysis, the study explores the electronic structure and nature of the reactions under an external electric field (EEF). Analysis using the activation strain model highlights the significant influence of geometrical deformation energies of FLPs on the activation barriers of H2 activation reactions. Computational results suggest that H2 activation by FLP molecules follows the electric field mechanism, indicating the potential of the FLP/EEF combination as an effective activator for inert molecules.

Insights into the mechanism, selectivity, and substituent effects in the Diels-Alder reaction of azatrienes with electron-rich dienophiles: An MEDT study

The reactivity and mechanistic intricacies of azatrienes in Diels-Alder reactions have been relatively unexplored despite their intriguing potential applications. In this study, we employ Molecular Electron Density Theory to theoretically investigate the hetero-Diels–Alder reaction involving azatrienes with ethyl vinyl ether and allenyl methyl ether. Analysis of Conceptual Density Functional Theory, energetic profiles, and the topological characteristics is conducted to elucidate the reactions. The revealed mechanism manifests as a polar one-step two-stages process under kinetic control. We establish a clear relationship of between the periselectivity, regioselectivity, and stereoselectivity on one hand and the characteristics of the reactions mechanism on the other hand. The influence of weak interactions on reaction activation barriers and bonding evolution are discussed in detail. We demonstrate that substituents enhancing the reverse electron density flux facilitate the feasibility of the reactions. The results lay ground for a meticulous control of the reaction of azatriene in similar synthetic scenarios.

DFT Simulations on the Nitrogen Reduction Reaction Activity of Transition Metal Nitride and Oxynitride

Transition metal nitride (TMN) is a promising material towards the energy related applications including catalysis and energy storage.1 The sluggish nitrogen reduction reaction (NRR) due to the high energy input to activate N2 remains a significant challenge for NRR electrocatalysts. The surface N of TMN can be a solution to this with initial N vacancy formation via hydrogenation steps and ammonia formation. In addition, with a small amount of surface oxygen present in the catalyst surface, the resulting oxynitride seems very interesting and active towards NRR.2 But the mechanism behind this is not yet understood.In this study, we first focused on the modelling of the structure of metal nitride (ZrN) and oxynitride (ZrOxNy/ZrN) surfaces. The structure of oxynitride is obtained by running molecular dynamics (MD) calculations at both room temperature and experimental deposition temperature (90°C and 750°C). NRR reaction is then studied via the Mars-Van Krevelen (MvK) mechanism with introducing surface N vacancy and subsequent N2 adsorption and N filling. With computing the reaction energy and activation barriers of key reaction steps on both ZrN and ZrOxNy/ZrN, we can find a clue on how surface N of TMN helps to activate N2 and the role of small amount of surface oxygen on activating N2. To study the origin of small amount of oxygen, reaction energies and full reaction pathway along the deposition process are computed and plotted. Finally, dopant effect will be modeled with transition metal dopants (e.g. Cu and Hf) at surface region to study any localized electronic effect on NRR.These results can be useful to design and deposit ZrN acting as effective NRR electrocatalysts.

Double-proton transfer triggering mechanism of nitromethane caused by intermolecular hydrogen bonding at low temperature

The initial triggering mechanism of nitromethane is investigated by first-principles molecular dynamics simulations and temperature-dependent Raman spectroscopy experiment. The Raman spectra at different temperature are obtained by Car-Parrinello molecular dynamics simulation to explore the activated vibration modes caused by low-temperature heat. The temperature-dependent Raman spectra experiment is constructed to compare with the theoretical data. Each possible initial reaction path caused by the activated vibration mode is analyzed to reveal the triggering mechanism of the initial chemical bond breaking for nitromethane. The results show that the intermolecular double-proton transfer is the first reaction step which is triggered by the intermolecular hydrogen bond reinforced with the active C–H stretching vibration (near 3000 cm−1), which is not reported before. The scanning energy barrier related to the increase of C–H bond lengths is about 60 kcal/mol, which is consistent with the calculated activation barrier (59.8 kcal/mol) of intermolecular proton transfer reaction. This proves the reliability of our conclusions. The results provide a new interpretation for the long-debated initial decomposition mechanism of nitromethane.

Importance of hydrogen bonding in base-catalyzed transesterification reactions with vicinal diols

The transesterification reaction kinetics of 2-(benzoyloxy)ethyl benzoate with various alcohols (ethylene glycol, 1,3-propanediol, 1-butanol, propylene glycol and 1,2-butylene glycol) using various cyclic amidine catalysts were investigated. For transesterification with excess glycol (glycolysis), the rate was nearly zero order in diester and glycol concentration, which is substantially different from classical transesterification kinetics with mono-alcohols. The measured kinetic parameters during glycolysis are consistent with a reaction path that is kinetically limited by the decomposition of the reaction intermediate formed from the alkoxide and diester. The DFT-calculated reaction energy and activation barrier for decomposition of this intermediate reveal a critical role of intramolecular hydrogen-bond stabilization made possible by the vicinal –OH of the glycol that effectively increases the concentration of the intermediate during reaction resulting in acceleration of the overall transesterification rate. These findings indicate the nature of both the alcohol solvent and the catalyst influence transesterification rate, and results suggest they are also important in the deconstruction of carbonyl-containing condensation polymers.

Mechanism of Interaction of Nitro Compounds with Olefins in Acetonitrile

The interaction of 4-fluorostyrene with 4-CN-PhNO2 in the presence of various solvents has been simulated by quantum chemistry methods. The reaction mechanism and activation barriers of its stages are proposed. The software package Gaussian03 was used for calculations. The optimal geometric parameters of the structures under study were obtained by means of the DFT/WB97XD/DGDZVP2 methods, the TDSCF/DFT/WB97XD/DGDZVP2 and TD-SCF/DFT/PBEPBE/6-311g++(3d2f,3p2d) methods were used to calculate excited singlet and triplet states, and the IEFPCM model was employed to account for the solvent effects. The transition states were calculated by the TS method using the DFT/PBEPBE/6-311g++(3d2f,3p2d) method.

Insights into Electrolyte Reactivity and Solid Electrolyte Interphase Formation at the Li Metal Anode Surface from DFT Simulations

Solid electrolyte interphase (SEI) is a critical component of lithium ion batteries, yet is poorly characterized and not well understood. We use plane wave density functional theory simulations to perform a comprehensive study of the degradation reaction mechanisms of four electrolyte solvents and additives, ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and vinylene carbonate (VC), at the Li (001) metal anode surface. The calculations provide fundamental insights into electrolyte decomposition and spontaneous SEI formation. Utilizing automated workflows implemented in the Schrödinger Materials Science Suite, we compute the adsorption energies and calculate the reaction energies for each decomposition pathway. Furthermore, we employ nudged elastic band calculations to compute the decomposition reaction barriers and provide mechanistic insights into the onset of SEI formation. We analyze trends in decomposition reaction energies and the relationships between the reaction energies and the activation barriers for the various electrolyte molecules as a function of applied bias potential. We find that the preferred decomposition pathways are different for the solvent molecules (EC and PC) than for the additives (FEC and VC). Calculations also suggest that applied bias reduces decomposition reaction barriers thus enhancing SEI formation. Such a comprehensive dataset of reaction energies and activation barriers provides useful benchmarks for the development and validation of reactive machine learned force fields for modeling advanced battery chemistries at a larger scale.

Reactivity of the Intramolecular Vicinal Group-13/P- and B/Group-15-Based Frustrate Lewis Pairs with Sulfur Dioxide: Mechanistic Insight from DFT.

The emission of SO2 gas by industrialized societies contributes to the occurrence of acid rain in natural environments. In this study, we put forward a theoretical investigation into the capture reactions of SO2. Our analysis centers on the energy profiles of intramolecular 1,2-cyclohexylene-bridged FLP-associated molecules. We will particularly examine the reactions involving G13/P-based (with G13 denoting Group 13 element) and B/G15-based (with G15 representing Group 15 element) FLP-associated molecules. Except for Tl/P-FLP, B/N-FLP, and B/Bi-FLP, our theoretical examinations indicate that the remaining six FLP-associated molecules, namely G13'/P-FLP (G13' = B, Al, Ga, and In) and B/G15 ' -FLP (G15' = P, As, and Sb), can easily undergo SO2 capture reactions due to their energetic feasibility. Particularly, our theoretical findings suggested that 1,2-cyclohexylene-bridged Al/P-FLP, Ga/P-FLP, B/As-FLP, and B/Sb-FLP are capable of undergoing a reversible reaction and returning to the initial reactant state. Our theoretical evidence indicates that the G13-G15 bond length in the 1,2-cyclohexylene-linked G13/G15-FLP can serve as a basis for evaluating the free activation barrier associated with its reaction with SO2. Two theoretical methods, namely, the frontier molecular orbital theory and the energy decomposition analysis-natural orbitals of chemical valence approach, are utilized to investigate the electronic structure and bonding nature of the reactions under consideration. Moreover, the analyses based on the activation strain model revealed that it is the geometrical deformation energies of G13/G15-FLP, which is the key factor that greatly influences the activation barriers of such SO2 capture reactions. Further, our theoretical computations indicate that such capturing reactions of SO2 by intramolecular 1,2-cyclohexylene-linked G13/G15-based FLP-type molecules obey the Hammond postulate.

Mean field model parameterization to recover coverage-dependent kinetics

Lateral interactions between adsorbates introduce coverage dependence into adsorption energies and activation barriers of surface reactions. Lattice-based kinetic Monte Carlo (kMC) simulations can capture these interactions quantitatively but are laborious to parameterize and solve. Mean field models are more tractable, but protocols to construct and parameterize them are unclear. Here we explore the ability of a coverage-aware mean-field model to map to a lattice-kMC model of a generic two-step reaction network, including quasi-equilibrated adsorption and rate-limiting dissociation steps. We derive expressions for mean-field and coverage-dependent adsorption energies and dissociation barriers and parameterize against lattice-kMC predictions. We show that the parameterized mean-field rates correlate with ground truth lattice-kMC results across a wide range of reaction conditions and identify regions where the mean field fails. The mean field model similarly captures kMC-derived rate-order, Arrhenius and Sabatier plots at a greatly reduced computational cost. The results provide guidance for parameterizing mean-field models, benchmarked against explicit lattice-based approaches for incorporating the influence of coverage effects.

A quantum chemical perspective on the potential application of Fe-decorated C24N24 porous fullerene for catalytic ethylene epoxidation

Density functional theory calculations are used to investigate the reaction mechanisms and activation barriers of ethylene (C2H4) epoxidation by molecular oxygen (O2) using Fe-decorated C24N24 porous fullerene. Calculated adsorption energies demonstrate that the decorated Fe atom has a greater propensity to adsorb O2 molecules than C2H4. The results, on the other hand, indicate that ethylene epoxidation by O2 proceed through the Langmuir Hinshelwood (LH) mechanism. The whole ethylene epoxidation reaction is exothermic, with activation energies ranging from 0.36 to 0.68 eV, showing that this process is both thermodynamically and kinetically favorable. The side reaction, i.e., formation of acetaldehyde, is almost impossible over the proposed catalyst due to its large activation energy.

Cooperative Activation of Small Molecules by Base-Stabilized Borylenes.

Computational investigations were carried out using density functional theory (ωB97XD(toluene)/6-311+G*) on a series of base-stabilized borylenes to understand their ligand properties and potential toward the activation of enthalpically strong E-H bonds (E = H, NH2, SiH2Ph, and CH3) as well as binding with small molecules such as CO and CNMe. The calculated reaction free energies and activation barriers suggest the ability of hitherto unexplored carbene-stabilized borylenes to not only split such bonds but also bind with CO and CNMe. A detailed mechanistic study of these bond activation processes reveals the noninnocent behavior of the carbene moiety attached to the boron center, thereby leading to cooperative splitting of the bonds of interest. The binding of CO and CNMe to the base-stabilized borylenes was investigated by energy decomposition analysis (EDA) with natural orbitals for chemical valence (NOCV), which gave appreciable interaction energy (ΔEint) values, thereby indicating strong binding of CO and CNMe to these borylenes.

Heterostructured mixed metal oxide electrocatalyst for the hydrogen evolution reaction.

The hydrogen evolution reaction (HER) has attracted considerable attention lately because of the high energy density and environmental friendliness of hydrogen energy. However, lack of efficient electrocatalysts and high price hinder its wide application. Compared to a single-phase metal oxide catalyst, mixed metal oxide (MMO) electrocatalysts emerge as a potential HER catalyst, especially providing heterostructured interfaces that can efficiently overcome the activation barrier for the hydrogen evolution reaction. In this mini-review, several design strategies for the synergistic effect of the MMO catalyst on the HER are summarized. In particular, metal oxide/metal oxide and metal/metal oxide interfaces are explained with fundamental mechanistic insights. Finally, existing challenges and future perspectives for the HER are discussed.

First-principles insights into sulfur oxides (SO2 and SO3) adsorption and dissociation on layered iron sulfide (FeS) catalyst

The adsorption of sulfur oxides (SOx) represents the fundamental step towards their conversion to lower-risk sulfur-containing species. Herein, we investigate the adsorption and dissociation mechanism of sulfur dioxide (SO2) and sulfur trioxide (SO3) on layered iron sulfide (FeS) nanocatalyst (001), (011), and (111) surfaces using density functional theory methodology. Both SO2 and SO3 exhibit strong reactivity towards the (011) and (111) surfaces, with the most stable geometry for SO2 and SO3 on the (011) surface predicted to be a tridentate η23(S,O,O) and a bidentate η22(O,O) configuration, respectively, whereas on the (111) surface, they are predicted to be coordinated in a monodentate η21(S) and η21(O) geometry, respectively. Significant charge donation from the FeS surface to the SOx species is observed, which resulted in elongation of S−O bond lengths, confirmed by vibrational frequency analyses. Favourable reaction energy and activation barrier is predicted for SO2 dissociation at the (111) surface.

Ultrathin MoS2 nanosheets decorated on NiSe nanowire arrays as advanced trifunctional electrocatalyst for overall water splitting and urea electrolysis

Developing highly-efficient and low-cost electrocatalysts act as pressing impacts on the flourishing of hydrogen energy, including electrochemical water splitting is a kind of prevailing energy conversion technology. However, it is hampered by the high activation barrier of oxygen evolution reaction (OER). Herein, a hybrid electrocatalyst with trifunctional and 3D core–shell structure is designed by hydrothermal process in order to achieve outstanding OER, hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) properties. NiSe@MoS2/NF catalyst is composed of the heterogeneous interface formed by NiSe nanowire arrays which supported by nickel foam and MoS2 nanosheets. The synergistic effect and strong electronic interaction between the interface display the dominant impact of OER, HER and UOR. Especially in basic electrolyte, the potential is as low as 310 mV at 100 mA cm−2, even Tafel slope is 70.8 mV dec-1, representing the predominant OER property. The HER and UOR also demonstrate enormous prospect with 210, 233 mV at 100 mA cm−2. When NiSe@MoS2/NF||NiSe@MoS2/NF catalyst as anode and cathode, only requires potential of 1.48 V at 10 mA cm−2 for overall water splitting test. The work offers a plain, high-efficiency and inexpensive method to evolve the progressive trifunctional electrocatalysts for other energy-related applications.

In situ formation of cocatalytic sites boosts single-atom catalysts for nitrogen oxide reduction

Nitrogen oxide (NOx) pollution presents a severe threat to the environment and human health. Catalytic reduction of NOx with H2 using single-atom catalysts poses considerable potential in the remediation of air pollution; however, the unfavorable process of H2 dissociation limits its practical application. Herein, we report that the insitu formation of PtTi cocatalytic sites (which are stabilized by Pt-Ti bonds) over Pt1/TiO2 significantly increases NOx conversion by reducing the energy barrier of H2 activation. We demonstrate that two H atoms of H2 molecule are absorbed by adjacent Pt atoms in Pt-O and Pt-Ti, respectively, which can promote the cleave of H-H bonds. Besides, PtTi sites facilitate the adsorption of NO molecules and further lower the activation barrier of the whole de-NOx reaction. Extending the concept to Pt1/Nb2O5 and Pd1/TiO2 systems also sees enhanced catalytic activities, demonstrating that engineering the cocatalytic sites can be a general strategy for the design of high-efficiency catalysts that can benefit environmental sustainability.

Synergetic effects of Fe[sbnd]N[sbnd]C and LiFePO4 in modified separator on improved adsorption and catalytic conversion reaction of soluble LiPSs for Lithium-sulfur batteries

“Shuttle effect” is a serious obstacle in the development of high-performance lithium-sulfur batteries and modified separator is considered an effective strategy to prevent the shuttle effect of soluble polysulfides (LiPSs). Herein, we demonstrate a modified polypropylene (PP) separator composed of nitrogen-doped carbon coated LiFePO4 (NC-LFP), Ketjen black carbon (KB) and polyvinylidene fluoride (PVDF) (NC-LFP interlayer), which can improve adsorption and catalytic conversion toward LiPSs. The analysis shows that NC-LFP interlayer could effectively adsorb LiPSs and therefore suppress its shuttle effects due to the FeNC functional groups in the nitrogen-doped carbon coated on LFP polar particles. The DFT analysis and the electrochemical performance test demonstrate the FeNC functional groups in NC-LFP interlayer provide lower activation barrier for catalytic conversion reaction of LiPSs to Li2S and vice versa. The coin cells with NC-LFP modified separator exhibit an initial discharge specific capacity of 907 mAh/g at 1C. After 500 cycles, the specific capacity is 702 mAh/g with a retention rate of 79.5 %. Moreover, at 8C rate, the discharge-specific capacity of 667.5 mAh/g is achieved. The use of NC-LFP interlayer modified separators realizes lithium-sulfur batteries with long-cycle life and high-rate performance, providing an emerging strategy for high-performance Li-S batteries.

A theoretical study of the NbS2 monolayer as a promising anchoring material for lithium-sulfur batteries.

Developing efficient cathode materials with good conductivity to restrain the shuttle effect and promote the reaction kinetics has been a key scientific issue for the development of lithium-sulfur (Li-S) batteries. Here, by means of first-principles computations, we demonstrate that the NbS2 monolayer is a promising cathode anchoring material for Li-S batteries. It has a metallic feature that improves the conductivity of sulfur and lithium polysulfides (LiPSs) and promotes the electron transfer ability. The discharge products LiPSs are strongly anchored on the NbS2 monolayer without structural distortion, which effectively alleviates the shuttle effect. Remarkably, the reductions of sulfur to soluble LiPSs are spontaneous exothermic reactions while the subsequent reductions to insoluble LiPSs are endothermic reactions with low Gibbs free energy barriers (0.09-0.18 eV) and reaction activation barriers (0.83-0.93 eV), ensuring the rapid discharge process. In addition, the barriers of Li2S decomposition and Li atom diffusion are only 0.64 and 0.18 eV, respectively, which improve the reaction kinetics in the charging process and the cycling life of batteries. These results suggest that the NbS2 monolayer can be utilized as a promising anchoring material for Li-S batteries to achieve high reversible capacity and conversion efficiency.

Nickel-decorated RuO2 nanocrystals with rich oxygen vacancies for high-efficiency overall water splitting.

Designing transition metal-oxide-based bifunctional electrocatalysts with excellent activity and stability for OER/HER to achieve efficient water splitting is of great importance for renewable energy technologies. Herein, a highly efficient bifunctional catalysts with oxygen-rich vacancies of nickel-decorated RuO2 (NiRuO2-x) prepared by a unique one-pot glucose-blowing approach were investigated. Remarkably, the NiRuO2-x catalysts exhibited excellent HER and OER activity at 10mAcm-2 in alkaline solution with only a minimum overpotential of 51mV and 245mV, respectively. Furthermore, the NiRuO2-x overall water splitting exhibited an ultra-low voltage of 1.6V to obtain 10mAcm-2 and stability for more than 10h. XPS measurement and theoretical calculations demonstrated that the introduction of Ni-dopant and oxygen vacancies make the d-band center to lie close to the Fermi energy level, the chemical bonds between the active site and the adsorbed oxygen intermediate state are enhanced, thereby lowering the reaction activation barriers of HER and OER. The assembly of solar-driven alkaline electrolyzers facilitate the application of the NiRuO2-x bifunctional catalysts.

Remarkable Single Atom Catalyst of Transition Metal (Fe, Co & Ni) Doped on C2N Surface for Hydrogen Dissociation Reaction.

Currently, hydrogen is recognized as the best alternative for fossil fuels because of its sustainable nature and environmentally friendly processing. In this study, hydrogen dissociation reaction is studied theoretically on the transition metal doped carbon nitride (C2N) surface through single atom catalysis. Each TMs@C2N complex is evaluated to obtain the most stable spin state for catalytic reaction. In addition, electronic properties (natural bond orbital NBO & frontier molecular orbital FMO) of the most stable spin state complex are further explored. During dissociation, hydrogen is primarily adsorbed on metal doped C2N surface and then dissociated heterolytically between metal and nitrogen atom of C2N surface. Results revealed that theFe@C2N surface is the most suitable catalyst for H2 dissociation reaction with activation barrier of 0.36 eV compared with Ni@C2N (0.40 eV) and Co@C2N (0.45 eV) complexes. The activation barrier for H2 dissociation reaction is quite low in case of Fe@C2N surface, which is comparatively better than already reported noble metal catalysts.

Computational Investigation of Site-Dependent Activation Barriers of Zeolite-Catalyzed Protolytic Cracking Reactions

Proton-exchanged zeolites are effective Brønsted-acid catalysts that exhibit molecular-level shape selectivity. Yet, the nonuniform, heterogeneous porous environment makes it challenging to understand and predict site-dependent reactivity that originates from the intricate, noncovalent interactions exerted by the catalyst pore walls, especially with large, flexible reactants. In this work, we developed a computational procedure consisting of generating quasi-transition-state (TS) complexes using force-field-based configurational-biased sampling and subsequent reaction path optimization using a density-functional theory-based nudged-elastic-band method. This approach allows us to capture how the TS configurations adapt to the local environment and to obtain a rough estimate of TS entropy via the number of accessible TS configurations at each active site. The resulting site-dependent TS energetics further enable the calculation of ensemble-averaged activation barriers. Using this approach, we studied the protolytic cracking of n-butane in TON, MFI, LTA, and FAU zeolites. It is found that in the MFI zeolite, while the tighter zig-zag and straight channels have lower TS energies, the more spacious intersection region potentially supports a much larger number of TS configurations. In addition, it is also found that if the reactant state is restricted to the vicinity of an active site, the computed site-specific barriers show a large variation across different zeolites and among different sites within the same zeolite, with values ranging from 182 to 218 kJ/mol. We argued that for kinetics-limited reactions, the reactant state should be taken to be the globally most stable configuration and showed that this treatment leads to ensemble-averaged barriers that are substantially more similar across zeolites, with the FAU and LTA zeolites having intrinsic barriers around 220 kJ/mol and the MFI and TON zeolites around 200 kJ/mol.