Low Activation Energy Barrier Research Articles

Two-dimensional conductive π-conjugated metal-organic frameworks as promising electrocatalysts for highly efficient hydrogen evolution reaction

Two-dimensional conductive π-conjugated metal-organic frameworks (2D c-MOFs), as a new promising electrocatalytic materials, have spurred great research interests, but the systematic research on the structure-property relationship of c-MOF-based electrocatalysts is scarcely reported. Herein we conduct a first-principles study on the screening of a family of 2D c-MOFs (TM3(HITN)2) as HER electrocatalysts, which are constructed by TM atoms and 2,3,8,9,14,15-hexaiminotrinaphthylene (HITN) functional groups. The data suggests that all these 2D TM3(HITN)2 possess metallic with good conductivity for electrochemical reactions due to their intrinsic π-electron conjugation and sufficient interaction between the TM atoms and the organic linkers. Through the complete computational screening, the Zr3(HITN)2 stands out because of its near-zero ΔG*H value and low activation energy barrier. Moreover, the distinguished HER performance of Zr3(HITN)2 can be attributed to the extremely enhanced electron density derived from the C-2p orbitals near the Fermi level accompanied by the size increase of the tri-dentated aromatic linkers. Hence, this study not only highlights a family of promising 2D c-MOF electrocatalysts toward HER, but also supplies a valuable insight on the design of novel and high-performance c-MOF-based materials for better electrocatalysis.

Embedding amorphous SnS in electrospun porous carbon nanofibers for efficient potassium storage with ultralong cycle life

Potassium-ion batteries (PIBs) have gained substantial research interest for scalable and affordable stationary applications owing to their low cost, natural abundance, and high energy density. However, the large size of potassium (K) ion hampers its diffusion and causes significant strain in conventional electrode materials, resulting in low capacity, poor rate capability, and short lifespan. Herein, we develop a new strategy by confining amorphous tin sulfide (a-SnS) in electrospun porous carbon nanofibers (denoted as a-SnS@pCNFs) to realize the highly reversible potassiation/depotassiation of SnS. The amorphous nature of a-SnS enables a lower activation energy barrier towards structural rearrangement during any possible conversion reaction, which facilitates an increased electrochemical stability. Moreover, the pCNF skeleton not only improves the overall electrical conductivity of a-SnS@pCNFs, but also accommodates the volume variation of the SnS during the repeated cycles of charge/discharge. Combining these benefits of a-SnS and the tailored pore structures in pCNFs, the a-SnS@pCNFs composite delivers a high reversible capacity (∼300 mAh g−1 at 1 A g−1), a remarkable rate capability (∼85.4 mAh g−1 at 10 A g−1) and an ultralong lifespan (2000 cycles at 3 A g−1). This work provides a viable strategy to stabilize the conversion and alloying materials with fast and reversible K-ion storage towards practical applications.

Density functional theory study of P-embedded SiC monolayer as a robust metal free catalyst for N2O reduction and CO oxidation

In this work, spin-polarized density functional theory calculations are conducted to evaluate the possible applicability of a single P atom doped silicon carbide (P-SiC) monolayer for reduction of nitrous oxide (N2O). The calculations show that P-doping in SiC monolayer is energetically favorable, and the resulting P-SiC is both dynamically and thermodynamically stable. According to our findings, N2O spontaneously dissociates when it interacts with the P-SiC from its O site without the need for an energy barrier, releasing -2.59 eV of energy. The adsorption energy of CO molecule on the P-SiC is less negative than that of N2O, implying that N2O will predominately occupy the catalyst surface. The CO + Oad reaction is used to remove the remaining oxygen atom (Oad) from the P-SiC surface. The calculations show that the reaction proceeds through a low activation energy barrier of 0.33 eV, which is much lower than the previously reported catalysts. This demonstrates the high catalytic activity of P-SiC surface. Furthermore, the adsorption of H2O and O2 species on the P-SiC nanosheet is investigated. The results show that the presence of these species has no effect on the catalytic activity of the P-SiC surface for N2O reduction. These results show that the proposed novel P-SiC catalyst can be regarded as an efficient material in the development of promising active catalysts for N2O elimination from the environment.

Ni-Al mixed metal oxide with rich oxygen vacancies: CO methanation performance and density functional theory study

Ni-Al mixed metal oxides have been successfully prepared by high shear mixer (HSM) and coprecipitation (CP) methods for low temperature CO methanation. In this work, Ni-Al (HSM-CP) catalyst presented small Ni crystallite size and high surface area, which all contribute to the methanation reaction at low temperature conditions. The obtained Ni-Al (HSM-CP) sample exhibited a mass of defective oxygen, thereby accelerating the dissociation of CO and ultimately increasing the activity of the catalyst. Ni-Al (HSM-CP) catalyst offered the best activity with CO conversion = 100% and CH 4 selectivity = 93% at 300 °C, and the CH 4 selectivity can reach 81.8% at 200 °C. In situ Fourier transform infrared spectroscopy and density functional theory show that CHO and COH intermediates with lower activation energy barriers are produced during the reaction, and hydrogen-assisted carbon–oxygen bond scission is more favorable.

Packaging contests between viral RNA molecules and kinetic selectivity.

The paper presents a statistical-mechanics model for the kinetic selection of viral RNA molecules by packaging signals during the nucleation stage of the assembly of small RNA viruses. The effects of the RNA secondary structure and folding geometry of the packaging signals on the assembly activation energy barrier are encoded by a pair of characteristics: the wrapping number and the maximum ladder distance. Kinetic selection is found to be optimal when assembly takes place under conditions of supersaturation and also when the concentration ratio of capsid protein and viral RNA concentrations equals the stoichiometric ratio of assembled viral particles. As a function of the height of the activation energy barrier, there is a form of order-disorder transition such that for sufficiently low activation energy barriers, kinetic selectivity is erased by entropic effects associated with the number of assembly pathways.

Non-energetic Formation of Ethanol via CCH Reaction with Interstellar H2O Ices. A Computational Chemistry Study.

Ethanol (CH3CH2OH) is a relatively common molecule, often found in star-forming regions. Recent studies suggest that it could be a parent molecule of several so-called interstellar complex organic molecules (iCOMs). However, the formation route of this species remains under debate. In the present work, we study the formation of ethanol through the reaction of CCH with one H2O molecule belonging to the ice as a test case to investigate the viability of chemical reactions based on a “radical + ice component” scheme as an alternative mechanism for the synthesis of iCOMs, beyond the usual radical–radical coupling. This has been done by means of DFT calculations adopting two clusters of 18 and 33 water molecules as ice models. Results indicate that CH3CH2OH can potentially be formed by this proposed reaction mechanism. The reaction of CCH with H2O on the water ice clusters can be barrierless (because of the help of boundary icy water molecules acting as proton-transfer assistants), leading to the formation of vinyl alcohol precursors (H2CCOH and CHCHOH). Subsequent hydrogenation of vinyl alcohol yielding ethanol is the only step presenting a low activation energy barrier. We finally discuss the astrophysical implications of these findings.

Designing a durable high-rate K0.45Ni0.1Fe0.1Mn0.8O2 cathode for K-ion batteries: A joint study of theory and experiment

K-ion batteries (KIBs) hold great promise for large-scale energy storage. However, the absence of suitable cathode materials limits their practical application. Meanwhile, rationally designing advanced cathode materials for KIBs remains an open question. In this work, based on density functional theory calculations, we find that the bond stability of Fe−O is higher than that of Co−O in layered transitional metal (TM) oxides. Additionally, the K-ion migration in the Fe-based layered TM oxide has a significantly lower activation energy barrier than that in the Co-based one. Based on this theoretical prediction, we successfully synthesized a low-cost K0.45Ni0.1Fe0.1Mn0.8O2 cathode, which shows excellent structural stability and superior K-storage properties, including durable cycle life and high-rate capability. Moreover, the designed K0.45Ni0.1Fe0.1Mn0.8O2 cathode possesses a great full-cell performance with a discharge capacity of ∼75 mA h g−1 and capacity retention of ∼80% after 100 cycles. The results show that Fe has better structural stability and K-ion diffusion than high-cost Co in layered oxide cathodes, and this finding provides new insights into the design of low-cost and high-performance KIB layered cathodes. This work highlights the feasibility of a theory-guided experiment in screening promising battery materials.

Co complex modified on Eupergit C as a highly active catalyst for enhanced hydrogen production

In present paper, the preparation and catalytic activity of Eupergit C polymer (EC) modified Co complex was reported. Scanning Electron Microscope (SEM), X-Ray Diffraction (XRD), Brunauer-Emmett-Teller Surface Area Analysis (BET), Fourier Transform Infrared Spectroscopy (FT-IR), Transmission Electron Microscopy (TEM) coupled with energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) were used to characterization of catalyst. EC modified-Co complex was the first time examined as a catalyst in NaBH 4 hydrolysis to H 2 evolution. The kinetic calculations were determined by using two different kinetic methods. The low activation energy barriers were achieved as 21.673 kJ mol −1 for nth order model and as 21.061kJmol −1 for Langmuir-Hinshelwood (L-H) model at low temperatures. EC modified-Co complex catalyst exhibited high performance with H 2 evolution rates of 3914 mL H 2 g cat −1 min −1 and 9183 mLH 2 g cat −1 min −1 at 30 °C–50 °C. Additionally, Langmuir–Hinshelwood mechanism was explained for EC modified Co complex catalyzed sodium borohydride hydrolysis reaction. The reusability experiments showed that EC modified-Co complex catalyst maintained excellent stability with 100% conversion and without significant lost after the 6th run. • Preparation of Eupergit C polymer (EC) modified Co complex catalyst. • The first time examination of EC modified Co complex catalyst in NaBH 4 hydrolysis. • Attainment to high H 2 evolution rate of 9183mL H 2 . g cat −1 min −1 at low temperature. • Achievement of low activation energy barriers of 21.673 and 21.061;kJmol −1 . • Excellent stability without significant lost after the 6th run in NaBH 4 hydrolysis.

Design metal-free single-atom catalyst P@BN for CO oxidation: A DFT-D study

Single-atom catalysts (SACs) have arisen significant interest in catalysis and have the superior advantage for CO oxidation. In the current study, beyond the normal single-metal atom catalyst, we designed a new type of metal-free single-atom catalyst based on P doped BN surface. The catalytic mechanism and electronic analysis of CO oxidation on P doped BN metal-free single-atom catalyst is studied by using DFT-D simulation. We found that the phosphorus is preferable to anchor on the boron vacancy of h-BN, and the 3p states of the P dopant would be the key to activate the pre-adsorbed O2. Due to the high catalytic performance and stability of metal-free single-atom, fast charge-transfer kinetics is permissible via catalysis. CO oxidation on the P doped Bv/BN is found to be feasible with the direct formation of CO2 from the cleavage of P–O bonds (ER2 pathway: O2 + CO → CO2 + O) and followed by the reaction process (O + CO → CO2) with low activation energy barriers, indicating that the CO oxidation might be ready at a low temperature. Our work is helpful to reveal the significant role of P dopant for the CO oxidation and shed light on design the new type metal-free single-atom catalyst with low cost, high-performance catalytic activities.

N2O Hydrogenation on Silver Doped Gold Catalysts, a DFT Study

In this study, the full reaction mechanism for N2O hydrogenation on silver doped Au(210) surfaces was investigated in order to clarify the experimental observations. Density functional theory (DFT) calculations were used to state the most favorable reaction paths for individual steps involved in the N2O hydrogenation. From the DFT results, the activation energy barriers, rate constants and reaction energies for the individual steps were determined, which made it possible to elucidate the most favorable reaction mechanism for the global catalytic process. It was found that the N2O dissociation occurs in surface regions where silver atoms are present, while hydrogen dissociation occurs in pure gold regions of the catalyst or in regions with a low silver content. Likewise, N2O dissociation is the rate determining step of the global process, while water formation from O adatoms double hydrogenation and N2 and H2O desorptions are reaction steps limited by low activation energy barriers, and therefore, the latter are easily carried out. Moreover, water formation occurs in the edges between the regions where hydrogen and N2O are dissociated. Interestingly, a good dispersion of the silver atoms in the surface is necessary to avoid catalyst poison by O adatoms accumulation, which are strongly adsorbed on the surface.

A computational study on the potential application of carbon nitride nanosheets in Na-ion batteries.

In the current study, the C3N monolayer, as a two-dimensional material, was considered as a suitable anode material in sodium-ion (Na-ion) batteries (NIBs) by performing first-principles density functional theory (DFT) computations. It was shown that the metallic feature of the Na-ion is retained after its adsorption onto various sites on the surface of the C3N monolayer. The C3N monolayer has negative adsorption energy values for the Na-ion. Afterwards, the C3N monolayer was shown to have a greater maximum theoretical capacity of 543.89 mAh/g for the Na-ion in comparison with other materials based on our computations. Due to the low activation energy barrier of approximately 0.112eV, migration of the Na-ion, which includes diffusion on the surface of the C3N monolayer, is rapid, demonstrating its great capability for fast charge-discharge processes. Ultimately, it was shown that, for the Na, the C3N monolayer possesses a low average open-circuit voltage, i.e., 0.83V. These results show that it is possible to utilize the C3N monolayer in NIBs as an anode material.

Solar assisted green photocatalysis for deducing carbamate insecticide from agriculture stream into water reclaiming opportunity

ABSTRACT ‘Ultraviolet’ and ‘Solar’ wastewater treatment units are used augmented with nanocrystals of magnetite, Fe2O3, which were previously synthesised via a cost-efficient co-perception route. The nanocrystals produced were used as a Fenton reagent source for the oxidising carbamate pesticide in aqueous solution through a combination of natural abundant solar radiation as well as artificial UV source. System parameters were examined and the optimal operating conditions were investigated to maximise the system yield. The objective optimisation was attained using a Box-Behnken factoring design (BBD) based on Response Surface Methodology, RSM. A mathematical model was developed and the maximal removal efficiency reached to 84.1% within 15 min of reaction time. Furthermore, the chemical oxygen demand was then investigated and it was oxidised and deduced to 57%. Analysis of the experimental data revealed that a second-order reaction model is best described the reaction kinetics. The calculated thermodynamic parameters suggested that the non-spontaneous nature of oxidation at high temperature was corroborated by positive Gibbs free energy change ∆G• and negative entropy, ∆S• values. Also, the negative values of enthalpy, ∆H•, indicated that the reaction was exothermic. The low activation energy barrier (−35.85 kJ/mol) indicated that the reaction proceeds at a low energy level.

DFT study on reaction mechanism of di-tert-butylphenol to di-tert-butylhydroxybenzoic acid

Experimental studies on the Kolbe–Schmitt reaction and its side reactions have made great progresses; however, the relative theoretical studies fall behind. In order to study the mechanism of the Kolbe–Schmitt reaction with 2,6-di-tert-butylphenol and 2,4-di-tert-butylphenol as reactants, we carried out theoretical calculation studies at the M06-2X/Def2-SVP/SMD level of theory using the Gaussian 09 D.01 software package. For the reactant 2,6-di-tert-butylphenol, there is a dynamic equilibrium between the main product and side product, which can rapidly transform into each other at 160 °C by crossing the Gibbs free energy barrier of 14.1 kcal/mol. Moreover, the relative Gibbs free energy of the main product and side product is close; both of them may be observed in the experimental system. However, for 2,4-di-tert-butylphenol, the main product is thermodynamically favorable due to its lower Gibbs free energy, while the side product is kinetically favorable due to the lower activation energy barrier; the main product and the side product compete with each other. We hope the study can shed light on the Kolbe–Schmitt reaction.

Porous Edge Confinement: High Carrier Potential and Low Activation Energy Barrier Synergistically Boosting the Efficiency of Selective Photocatalytic Co2 Conversion

Porous Edge Confinement: High Carrier Potential and Low Activation Energy Barrier Synergistically Boosting the Efficiency of Selective Photocatalytic Co2 Conversion

A novel PdC monolayer with fully dispersed Pd atoms and a rigid carbon backbone: an intrinsic versatile electrocatalyst for overall water splitting and the corresponding reverse reaction.

The electrocatalytic overall water splitting and the corresponding reverse reaction play a vital role in future renewable energy systems and, hence, are frontiers of catalysis research. In this work, we identify a heretofore unknown two-dimensional palladium carbide using the structure swarm intelligence algorithm. The proposed monolayer, named α-PdC, consists of fully dispersed Pd atoms and a rigid carbon backbone, exhibiting high mechanical, dynamical, and thermal stability with desirable electrical conductivity. Further calculations show that the proposed monolayer is an intrinsic multifunctional electrocatalyst. It possesses an excellent catalytic performance toward the hydrogen evolution reaction (HER), the oxygen evolution reaction (OER), and the oxygen reduction reaction (ORR) with low overpotentials. Specifically, the overpotential for the HER is only -0.01 V, and the significantly low activation energy barrier (0.16 eV) on α-PdC elucidates the fast kinetics. Moreover, α-PdC could also be highly active towards the OER and ORR with comparable overpotentials (0.38 and 0.27 V, respectively). This study identifies an intrinsic versatile electrocatalyst with potential applications in the fields of energy conversion and storage.

Quantum Mechanical Investigation on Decomposition Pathways of BuNENA

AbstractThe unimolecular decomposition pathways of n‐butyl nitroxyethylnitramine (BuNENA) were computationally investigated. The O−NO2 bond dissociation energies (BDEs) are found to be smaller than the N−NO2 BDEs. The consecutive NO2 elimination via TSA1 is more favorable kinetically than that via TSA2 although both of them form the same intermediate of n‐butyl‐aminoacetaldehyde (BuAAA). Isomerization of n‐butyl‐nitramineethyloxidanyl radical (BuNEȮ) formed by homolytic cleavage of O−NO2 bond was found to eliminate NO2 with a negative bond dissociation energy. Among the NO2 elimination pathways, the formation of C4H9NCH2 (PB2b), CH2O, and NO2 from BuNEȮ via the saddle point TSB2a was found to be the most kinetically favorable with a low activation energy barrier. In contrast, the consecutive HONO elimination is the most thermodynamically favorable with a high exothermicity (−▵H0). The first‐principle kinetic Monte Carlo (kMC) simulations show that the NO2 elimination of BuNEȮ via TSB2a plays an important role in driving the decomposition of BuNENA.

Intermetallic Nanocatalyst for Highly Active Heterogeneous Hydroformylation.

Hydroformylation is an imperative chemical process traditionally catalyzed by homogeneous catalysts. Designing a heterogeneous catalyst with high activity and selectivity in hydroformylation is challenging but essential to allow the convenient separation and recycling of precious catalysts. Here, we report the development of an outstanding catalyst for efficient heterogeneous hydroformylation, RhZn intermetallic nanoparticles. In the hydroformylation of styrene, it shows three times higher turnover frequency (3090 h-1) compared to the benchmark homogeneous Wilkinson's catalyst (966 h-1), as well as a high chemoselectivity toward aldehyde products. RhZn is active for a variety of olefin substrates and can be recycled without a significant loss of activity. Density functional theory calculations show that the RhZn surfaces reduce the binding strength of reaction intermediates and have lower hydroformylation activation energy barriers compared to pure Rh(111), leading to more favorable reaction energetics on RhZn. The calculations also predict potential catalyst design strategies to achieve high regioselectivity.

Molybdenum‐Promoted Surface Reconstruction in Polymorphic Cobalt for Initiating Rapid Oxygen Evolution

AbstractIt has been well recognized that the surface reconstruction of electrocatalysts at the initial stage in the form of phase transitions, defect migrations, valence regulations, etc., plays a critical role in generating real, surface active catalytic centers and achieving steady surface reactions. It is also expected that a low activation energy barrier for initiating surface reconstruction is crucial for rapid and stable electrochemical catalysis. Despite this, the surface reconstruction kinetics and their effects on catalytic reactions have been rarely investigated. Herein, using phase modulated polymorphic cobalt‐based catalysts with tailorable nitrogen‐metal bonds through a cationic molybdenum‐substitution strategy, real‐time X‐ray photoelectron spectroscopy (XPS) structural monitoring of the surface chemical state evolution during the catalytic reaction is performed to track the initial surface reconstruction kinetics during the alkaline oxygen evolution reaction (OER). It is concluded that the molybdenum‐modulated cobalt‐based nanocatalyst can be tuned with favorable initial surface reconstruction and stabilized active centers to reach optimized OER catalysis, accompanied by a low onset overpotential of only 210 mV and a favorable overpotential at 10 mA cm–2 of 290 mV, outperforming the commercial, noble‐metallic RuO2 catalyst. This study thus provides new conceptual insights into rationally regulating the initial surface reconstruction kinetics for high‐performance electrocatalysis reactions.

Room-temperature preparation of highly efficient NH2-MIL-101(Fe) catalyst: The important role of –NH2 in accelerating Fe(III)/Fe(II) cycling

The slow redox rate of Fe(III)/Fe(II) couples is a rate-limiting step for Fenton-like performance of Fe-MOFs. In this study, a series of catalysts (MIL-101) with various p-phthalic acid/2-aminoterephthalic acid (H2BDC/NH2–H2BDC) molar ratios were prepared using a simple and mild chemical method and applied for catalyzed degradation of bisphenol A (BPA). Interestingly, the –NH2 modified MIL-101(Fe) can adjust Fe-Oxo node by increasing the electron density of Fe(III) in the presence of –NH2 group with high electron density, thus forming Fe(II) in situ in MOFs. Meanwhile, the –NH2 groups used as electron-donors can promote electron transfer, resulting in faster Fe(III)→Fe(II) half-reaction and active H2O2 to continuously generate •OH radical. The BPA degradation and rate constant of Fe-BDC-NH2/H2O2 system are 15.4-fold and 86.8-fold higher than that of Fe-BDC/H2O2 system, respectively. The density functional theory (DFT) calculations showed that Fe-BDC-NH2 possesses higher Fermi level energy (−4.88 eV) and lower activation energy barriers (0.32 eV) compared with Fe-BDC. Moreover, Fe-BDC-NH2 showed good reusability and stability. This work offers a highly efficient and stable MOFs-based Fenton-like catalyst to rapidly degrade organic pollutants over a wide pH range for potential applications in wastewater treatment.

Rate enhancement of phenol hydrogenation on Pt by hydronium ions in the aqueous phase

Metal-containing zeolites exhibit remarkable catalytic activity for hydrogenation owing to the synergistic interactions between acid and metal sites. In the aqueous phase, the presence of water and, in particular, hydronium ions, complicate the adsorption of H2 and organic substrates. It is shown how hydrated hydronium ions formed from zeolite Brønsted acid sites promote the rate of hydrogenation of phenol on Pt by modifying reaction pathways in the aqueous phase. Hydrogen is preferentially added to the ortho-C of phenol at low concentrations of hydronium ions, while at high concentrations of hydronium ions hydrogen adds to both ortho- and para-C of phenol with equal probability. A proton coupled electron transfer (PCET) pathway is hypothesized to occur at metal surfaces associated with large concentrations of hydrated hydronium ions and adsorbed H, establishing a (quasi-) equilibrium open circuit potential. In the presence of lower concentrations of hydrated hydronium ions, the reaction follows a Langmuir-Hinshelwood mechanism in which adsorbed H atoms add to co-adsorbed phenol. DFT calculations show a lower activation energy barrier for the PCET pathway in the presence of hydronium ions compared to the pathway following a Langmuir-Hinshelwood type mechanism.