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Gas hydrates are a very promising energy source, but its exploitation also faces some challenges in marine geotechnics. The dissociation and formation of hydrates can significantly change the mechanical properties of sediment layers. Large-scale extraction of natural gas hydrate may trigger submarine landslides; therefore, an appropriate constitutive model is necessary for the safe exploitation of natural gas hydrates. In this paper, a bounding surface model of gas-hydrate-bearing sediments (GHBSs) is developed based on the modified Cam-clay model. The size of the bounding surface is related to hydrate saturation by introducing an additional hardening parameter. It is assumed that the additional hardening parameter is related to the hydrate saturation level and plastic volumetric strain. The method for determining the model parameters is given. The model is used to simulate the triaxial compression drainage test of GHBS under different test conditions. It is demonstrated that the model can adequately capture the main deformation characteristics of GHBS. The proposed model is implemented into a finite-element method software program, and finite-element modelling of the plane strain test is carried out. The comparison of results shows the validity of the model.

The impact of gas hydrate dissociation on submarine landslides has become an increasingly significant issue. However, previous models cannot interpret the newly discovered non-conformity between the slide surface and the base of the gas hydrate stability zone. Here, the authors design an experimental approach for visualising fluid migration during hydrate dissociation at atmospheric pressure. The results identify the lateral and vertical fluid migration pathways. Weak layers propagate nearly laterally beyond the hydrate zone, which lengthens the potential slide surface. Vertical pathways branch and deviate from their original paths, generating a shallower slide surface. Furthermore, the findings show that fluid overpressure under the overlying layer leads to steepening slopes. The lubrication effect and the underestimated inclination of slopes at failure may account for the low-angle failure of clay slopes. The results support a new conceptual model that reconciles the non-conformity between the slide surface and the base of the gas hydrate stability zone and offer a new perspective for the large-scale failure of low-angle submarine slopes. It will be interesting and important to confirm these implications in the future.

Safety plays an important role in determining the applicability of energetic compounds, and the bond dissociation enthalpy (BDE) of the “trigger bond” X-NO2 provides useful information to evaluate various safety properties. Accurate and rapid calculation of the BDE of X-NO2 is of great significance to perform the high-throughput design of energetic compounds, which becomes an increasingly popular means of materials design. We conduct a benchmark BDE calculation for 44 X-NO2 samples extracted from the iBond database, with the accuracies of 55 quantum chemistry calculation levels evaluated by the experimentally measured values. Only four levels have the global mean-absolute deviation (MAD) less than 10 kJ/mol, but no calculation level can achieve that all the local MADs of each category less than 10 kJ/mol. We propose a simple correction strategy for the original calculation deviations, and apply it to 30 calculation levels screened out through a series of accuracy assessments and obtain the corrected MAD

Although the direct synthesis of hydrogen peroxide (DSHP) is a potential alternative to the current anthraquinone auto-oxidation process, the low H2O2 selectivity of the former presents a major challenge. Previous studies have reported that the addition of halides improves the H2O2 selectivity of Pd-based catalysts. In this study, the H2O2 selectivity of Pd/SiO2 and PdBrx/SiO2 catalysts was observed to increase with the Br content. Furthermore, density functional theory (DFT) calculations on clean and Br-adsorbed Pd (1 1 1), (1 0 0), and (2 1 1) surfaces confirmed that the activation energies of the side reactions on the Pd (1 1 1) surface increased slightly after Br adsorption, whereas those of the main reactions were less affected. The repulsion between Br and O on the Pd (1 0 0) surface increased the O2 dissociation barrier by changing reaction configurations. Considering that the Pd (1 0 0) surface adsorbed O2 more strongly than did the Pd (1 1 1) surface, inhibiting O2 dissociation on the Pd (1 0 0) surface improved the H2O2 selectivity of PdBrx/SiO2 catalysts. On the Pd (2 1 1) surface, Br blocked an edge site and induced the reactions on the Pd (1 1 1) surface. In conclusion, DFT calculation confirmed that the repulsion and site blocking by adsorbed Br improved the H2O2 selectivity of PdBrx/SiO2 catalysts.

The catalytic properties of bifunctional ZSM-5@t-ZrO2 catalyst for methanol thiolation were revealed by using methanol and H2S as probe molecules. Taking the ZSM-5/t-ZrO2 physically-blended catalyst, pure ZSM-5 and t-ZrO2 as control catalysts, we investigated the characteristics of adsorption and transformation of different reaction molecules on or over different catalysts by combination of in-situ diffuse reflectance Fourier transform infrared spectroscopy (Drifts) and a variety of techniques including XRD, XPS, XRF, FT-IR, N2 adsorption-desorption, CO2/NH3-TPD, and DSC. The results showed that the synergistic effect of acid sites between ZSM-5 phase and t-ZrO2 phase in the bifunctional catalyst enhanced the adsorption and dissociation of methanol molecules, while the base sites in t-ZrO2 phase were mainly responsible for the adsorption and dissociation of H2S molecules. Due to the small specific surface area of pure t-ZrO2 catalyst, precursor species for sulfur deposition and carbon deposition were easily formed. Presulfurization could improve the initial activity of methanol thiolation and shorten the induction period. The dissociation of H2S at the base sites was the rate-determining step of the bimolecular reaction, and the appropriate increase of base sites in the bifunctional components could construct the matching formation rate of sulfhydryl and methoxy groups. At the same time, the special composite structure and meso-microporous system of ZSM-5@t-ZrO2 could effectively reduce the formation rate of carbon and sulfur deposits.

The cognition of active sites in the Ni-based catalysts plays a vital role and remains a huge challenge in improving catalytic performance of low temperature CO2 dry reforming of methane (LTDRM). In this work, typical catalysts of SiO2 and γ-Al2O3 supported Ni and Ni-Ce were designed and prepared. Importantly, the difference in the chemical speciations of active sites on the Ni-based catalysts is revealed by advanced characterizations and further estimates respective catalytic performance for LTDRM. Results show that larger [ Ni n 0 ] particles mixed with [Ni-O-Sin]) species on the Ni/SiO2(R) make CH4 excessive decomposition, leading to poor activity and stability. Once the Ce species is doped, however, superior activity (59.0% CH4 and 59.8% CO2 conversions), stability and high H2/CO ratio (0.96) at 600 °C can be achieved on the Ni-Ce/SiO2(R), in comparison with other catalysts and even reported studies. The improved performance can be ascribed to the formation of integral ( [ Ni n 0 ] -[CeIII-□-CeIII]) species on the Ni-Ce/SiO2(R) catalyst, containing highly dispersed [ Ni n 0 ] particles and rich oxygen vacancies, which can synergistically establish a new stable balance between gasification of carbon species and CO2 dissociation. With respect to Ni-Ce/γ-Al2O3(R), the Ni and Ce precursors are easily captured by extra-framework Aln-OH groups and further form stable isolated ( [ Ni n 0 ] -[Ni-O-Aln]) and [CeIII-O-Aln] species. In such a case, both of them preferentially accelerate CO2 adsorption and dissociation, causing more carbon deposition due to the disproportionation of superfluous CO product. This deep distinguishment of chemical speciations of active sites can guide us to further develop new efficient Ni-based catalysts for LTDRM in the future.

International audience; The mechanisms of H 2 dissociation on three stoichiometric anatase TiO 2 terminations, (001), (100) and (101), have been studied by means of density functional theory (PBE+U) calculations. A two-step process was considered: first, H 2 dissociation into H + and H − pair, and second the H − species migrates to a neighboring O site, transferring the electrons to the substrate. On (001), it shows the lowest activation barriers for hydrogen dissociation, 0.37 eV, whereas the highest value was found on (101), 0.98 eV. For hydrogen transfer from Ti to near O, the activation barriers are higher (from 1.10 to 2.37 eV), which indicates the dissociation step is kinetically more favorable than the H transfer process, although the latter is thermodynamically more favorable. Electronic structure, vibrational frequency analysis as well as temperature effects are studied to characterize the reactivity. The relationship between electronic structure, geometry and reactivity is analyzed by means of reactivity descriptors, and the results are compared with ceria and rutile TiO 2 facets.

Along this research the (110), (101) (200) and (211) surfaces were chosen to be studied by considering their atomic surface density. The surfaces were studied using CASTEP for the transition state search by DFT calculations, the initial coordinates that establish the SnO2-Methane distance were obtained with Adsorption Locator, a software able to calculate adsorption configurations using Monte Carlo methods. The results show that in terms of overall energy change, surface (101) presents the most favorable configuration with an exothermic total-energy change (form CH4 on the surface to a CO and H2O molecules on the surface) of − 18.47 kcal/mol, being the worst case the CH4 on a (200) surface with an endothermic total energy-change of 128.86 kcal/mol. In terms of the TS energy, the (101) surface remains as the most favorable system with energy maximums on the TS reaction path of 99.25 kcal/mol for the dissociation and adsorption of the CH4 molecule on the surface, and a maximum of 266.42 kcal/mol for the desorption and formation of the CH4 and H2O molecules on the SnO2 surface.

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 CH4 selectivity=93 % at 300 ℃, and the CH4 selectivity can reach 81.8 % at 200 °C. In situ Fourier transform infrared spectroscopy (FTIR) and density functional theory (DFT) 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.

Density functional theory (DFT) calculations have been performed to investigate the hydrogen dissociation and diffusion on Mg (0001) surface with Ni incorporating at various locations. The results show that Ni atom is preferentially located inside Mg matrix rather than in/over the topmost surface. Further calculations reveal that Ni atom locating in/over the topmost Mg (0001) surface exhibits excellent catalytic effect on hydrogen dissociation with an energy barrier of less than 0.05 eV. In these cases, the rate-limiting step has been converted from hydrogen dissociation to surface diffusion. In contrast, Ni doping inside Mg bulk not only does little help to hydrogen dissociation but also exhibits detrimental effect on hydrogen diffusion. Therefore, it is crucial to stabilize the Ni atom on the surface or in the topmost layer of Mg (0001) surface to maintain its catalytic effect. For all the case of Ni-incorporated Mg (0001) surfaces, the hydrogen atom prefers firstly immigrate along the surface and then penetrate into the bulk. It is expected that the theoretical findings in the present study could offer fundamental guidance to future designing on efficient Mg-based hydrogen storage materials.

Coherent light-matter interaction of molecular media in infrared (IR) cavities is a promising tool for manipulating and controlling chemical reactivity and light emission. We study the wavepacket dynamics of a single hydrogen fluoride (HF) molecule in electromagnetic environment, using the multiconfiguration time-dependent Hartree (MCTDH) method. We show that in the absence of additional thermal or coherent external sources, a single-mode cavity vacuum can efficiently dissociate a HF bond that is suddenly prepared in the vibrational ground level. We predict dissociation probabilities of up to 20% in less than 200 fs for a bare vacuum field that is resonant with the fundamental vibration frequency at the onset of the ultrastrong coupling regime. Additional enhancements of the dissociation probability can be expected for cavity with thermal excitations and multimode cavities. The results are understood analytically as the result of a Bloch-Siegert shift by using the extended-multi-level quantum Rabi model in a polaron frame that highlights the influence of the permanent dipole moments in the light-matter dynamics. Our work highlights the fundamental differences that can be expected for reactive dynamical processes inside infrared cavities and plasmonic nanostructures relative to free space.

Catechol pollutants (CATPs) serving as chelating agents could coordinate with many metal ions to form various CATPs-metal complexes. Little information is available on the effects of complexation of metal ions on CATPs degradation. This work presents a systematical study of •OH-mediated degradation of catechol and catechol-metal complexes over the whole pH range in advanced oxidation processes (AOPs). Results show that the pH-dependent complexation of metal ions (Zn2+, Cu2+, Ti4+ and Fe3+) promotes the deprotonation of catechol under neutral and even acidic conditions. The radical adduct formation (RAF) reactions are both thermodynamically and kinetically favorable for all dissociation and complexation species, and OH/ O− group-containing C positions are more vulnerable to •OH attack. The kinetic results show that the complexation of the four metal ions offers a wide pH range of effectiveness for catechol degradation. At pH 7, the apparent rate constant (kapp) values for different systems follow the order of catechol+Ti4+ ≈ catechol+Zn2+ > catechol+Cu2+ > catechol+Fe3+ > catechol. The mechanistic and kinetic results would greatly improve our understanding of the degradation of CATPs-metal and other organics-metal complexes in AOPs. The toxicity assessment indicates that the •OH-based AOPs have the ability for decreasing the toxicity and increasing the biodegradability during the processes of catechol degradation.

Nickel molybdate (NiMoO4) attracts superior hydrogen desorption behavior but noticeably poor for efficiently driving the hydrogen evolution reaction (HER) in alkaline media due to the sluggish water dissociation step. Herein, we successfully accelerate the water dissociation kinetics of NiMoO4 for prominent HER catalytic properties via simultaneous in situ interfacial engineering with molybdenum dioxide (MoO2) and doping with phosphorus (P). The as-synthesized P-doped NiMoO4/MoO2 heterostructure nanorods exhibit outstanding HER performance with an extraordinary low overpotential of −23 mV at a current density of 10 mA cm−2, which is highly comparable to the performance of the state-of-art Pt/C coated on nickel foam (NF) catalyst. The density functional theory (DFT) analysis reveals the enhanced performance is attributed to the formation of MoO2 during the in situ epitaxial growth that substantially reduces the energy barrier of the Volmer pathway, and the introduction of P that provides efficient hydrogen desorption of NiMoO4. This present work creates valuable insight into the utilization of interfacial and doping systems for hydrogen evolution catalysis and beyond.

The dissociation of gas hydrates can increase pore pressures greatly, thereby causing the shallow layers of submarine slopes to fail. Given the high failure risk of shallow subsea soils, it is important to understand the stratum response mechanisms after hydrate dissociation. In this paper, submarine slope failure triggered by overpressure fluid associated with gas hydrate dissociation is investigated in laboratory experiments. A two-layer geological model is built based on actual geological data, and pressurised air is injected into the model to simulate the overpressure fluid. The pore pressures, surface displacements and internal deformations of soils are measured and compared under different conditions, and their evolution processes are analysed for various parameter values. The results show that the accumulation of pore pressure increases with the thickness of the soil layer and leads to layered fractures. The failure pattern can be generalised into two types: (a) disc-shaped failure and (b) penetration failure. In disc-shaped failure, a major failure occurs when the shear stress reaches the shear strength, whereas tensile fracturing is a major effect in penetration failure. This achievement is very important for a deep understanding of submarine landslides induced by overpressure fluid, as well as for risk assessments of ocean engineering sites.

CO2 electroreduction reaction (CO2RR), combined with solid oxide electrolysis cells (SOECs), is a feasible technology for the storage of renewable electric energy, while its development is limited by the catalytic activity and stability on cathodes. Here, a novel garnet oxide (Gd3Fe5O12) cathode is designed, where the garnet oxide is converted to perovskite oxide and iron via in situ electrochemical phase transition during CO2 electroreduction, resulting in high activity with Faradaic efficiency close to 100% and great stability over 1000 h galvanostatic test. A variety of experimental characterizations and density functional theory calculations indicate that in situ exsolved Fe clusters can effectively enhance the adsorption energies of intermediates and lowering the CO2 dissociation barriers. Microkinetic modelling confirms that CO2RR goes through a dissociative adsorption mechanism and the electronic transfer for CO2 dissociation is the rate-determining step.

Summary Although advances in coating technologies have allowed us to match—or even exceed—the lubricity of Nature’s low-friction surfaces, the performance of synthetic materials inevitably diminishes over time as the surfaces are worn and damaged by irreversible breakage of covalent bonds. Synthetic systems lack the bespoke repair mechanisms that replenish hydration lubrication surfaces in Nature. Here, we demonstrate dynamic repair of low-friction surfaces prepared through a surface-selective self-assembly strategy. Monolayers of lubricating polymers associate with functionalized surfaces through strong and specific host–guest interactions, leading to hydration lubrication surfaces with low coefficients of friction (0.024–0.028). Following friction-induced dissociation of the polymers, the polymer-to-surface interaction is restored by the reformation of host–guest complexes, thus repairing the monolayer, renewing the lubricity, and reducing the effects of wear. Such dynamically restored low-friction materials will be an essential tool in decreasing global energy use—a fifth of which is expended overcoming friction.

SrFeO3-δ perovskite material is considered as a potential substitute for Ni-based fuel electrodes, while the problem of Sr segregation limits the development of material. Herein, different high-valence elements Ti4+, Nb5+and Mo6+ are gradient doped into La0.5Sr0.5FeO3-δ (LSF) to solve Sr segregation and study the influence mechanism for high valence elements. After the LSF is doped by high-valence elements, the reduction stability and CO2 tolerance are found to be obviously improved in a CO2:CO = 1:1 atm. Under the premise of stability, lower-valence element doping requires less Fe4+ reduction and lattice oxygen to match the charge, therefore, La0.5Sr0.5Fe0.9Ti0.1O3-δ (LSFTi5591) possesses more oxygen vacancies than La0.5Sr0.5Fe0.9Nb0.1O3-δ (LSFNb5591) and La0.5Sr0.5Fe0.9Mo0.1O3-δ(LSFMo5591). Since Ti ions possess a weaker binding force with O ions, LSFTi5591 more easily loses lattice oxygen and generates oxygen vacancies under high-temperature and reduction conditions, which results in stronger CO2 adsorption. Using LSCF-GDC as the oxygen electrode of electrolytic cells, the LSFTi5591 cell (1.35 A cm−2) exhibits higher electrochemical performance than LSFNb5591 (1.18 A cm−2) and LSFMo5591 (1.04 A cm−2) cells due to stronger CO2 adsorption and dissociation in the medium-frequency resistance range.

We have prepared well-resolved Nb n + (n = 1–10) clusters and report here an in-depth study on the essentially different reactivity with N2 and O2, by utilizing a multiple-ion laminar flow tube reactor in tandem with a customized triple quadrupole mass spectrometer (MIFT-TQMS). As results, the Nb n + clusters are found to readily react with N2 and form adsorption products NbnN 2 m + ; in contrast, the reactions with O2 give rise to NbnO 1 − 4 + products, and the odd-oxygen products indicate O-O bond dissociation, as well as increased mass abundance of NbO+ pertaining to oxygen-etching reactions. We illustrate how N2 prefers a physical adsorption on Nb n + clusters with an end-on orientation for all the products, and allow for size-selective Nb n + clusters to act as electron donor or acceptor in forming NbnN 2 m + . In contrast to these nitrides, the dioxides Nb n O 2 + display much larger binding energies, with O2 always as an electron acceptor, corresponding to superoxide or peroxide states in the initial reactions. Density-of-states and orbital analyses show that the interactions between Nb n + and O2 are dominated by strong π-backdonation indicative of incidental electron transfer; whereas weak π-backdonation and simultaneous σ donation interactions exist in Nb n N 2 + . Further, reaction dynamics analysis illustrates the different interactions for N2 and O2 in approaching the Nb n + clusters, showing the energy diagrams for N2 adsorption and O-O bond dissociation in producing odd-oxygen products. Fragment analyses with orbital correlation and donor-acceptor charge transfer are also performed, giving rise to full insights into the reactivities and interactions of such transition metal clusters with typical diatomic molecules.

Hypothesis Dynamic imine surfactants (DIS) can be constructed by the formation of dynamic imine bonds (Dibs) between aromatic aldehydes and aliphatic amines in water. Because of the nature of Dibs in water, a thermodynamic equilibrium state was achieved between the DIS and aldehyde and amine precursors to form a dynamic combinatorial library (DCL). When the DIS served as sole emulsifier to form oil–H2O emulsions, the precursors migrated between the H2O phase and the oil phase, which altered the DCL equilibrium. The DIS concentration and emulsion stability also changed. Experiments By mixing 4-(2-sulfobetaine-ethoxy)-benzaldehyde (SBBA) and aliphatic amines of CnH2n+1NH2 (n = 4, BA; n = 6, HA; n = 8, OA; n = 10, DA) in water, four amphoteric DIS (SBBA–BA/HA/OA/DA) were prepared. Dib formation was characterized using 1H NMR. The DIS surface activity was studied by surface tension and fluorescence probe methods. The reversible switching of DIS and its wormlike micelles were explored. Findings SBBA–OA (or SBBA–DA) DIS was not a suitable emulsifier for stable hydrocarbon (HC)–H2O emulsions. OA and DA were more soluble in the HC phase than the H2O phase. The precursors of OA and DA migrated from the H2O to the HC phase, and the thermodynamic equilibrium state of DCL shifted towards Dib dissociation. The Dib could be regenerated by HC phase removal. A novel strategy where volatile HC (such as pentane) was used as a trigger was developed to switch the DIS reversibly and its self-assemblies (such as wormlike micelles) in water without inorganic salt accumulation. The SBBA–HA (or SBBA–BA) DIS was a suitable emulsifier for stable emulsions because HA and BA were more soluble in the H2O phase.

In this study, Co2P/CoP hybrid nanoparticles (NPs) imbedded on the surface of core-shell metal-organic frameworks (MOFs) derived three-dimensional N, P co-doped graphitized carbon (Co2P/CoP@NPGC) are prepared via direct pyrolysis of P-containing MOF precursors. P dopant dosage is tailored to adjust active sites and crystalline phases of Co2P/CoP@NPGC. The active Co2P and CoP NPs and the synergistic effect from the Co-Nx/C and Co-P/C active sites and porous NPGC make the dominant contributions to the ORR/OER. For ORR, the half-wave potential of Co2P/CoP@NPGC-1 is 0.93V, which is superior to that of Pt/C (E1/2 = 0.875 V). As for OER, Co2P/CoP@NPGC-1 displays a lower overpotential (ƞ = 340 mV) compared to RuO2 (ƞ = 380 mV, at 10 mA cm-2). The Co2P@CoOOH heterojunction guarantees intrinsic conductivity. Furthermore, doping with N and P can modify the surface electronic structure of catalyst to lower the energy of oxygen adsorption and dissociation, which are beneficial to enhance the ORR and OER activity. Additionally, its bifunctional activity parameter (ΔE) for ORR and OER is only 0.64 V, which is lower than that of Pt/C and RuO2 (0.76 V). Therefore, this work proposes a new sight into constructing a competitive core-shell MOFs derived electrocatalyst for ORR/OER.

Design of the catalyst for efficient water dissociation and hydrogen recombination is paramount in enhancement of the alkaline water electrolysis kinetics. Herein, we reported a delicate hierarchical (VO)2P2O7-Ni2P@NF (VPO-Ni2P@NF) hybrid catalyst that operated efficiently in alkaline media. The VPO and Ni2P respectively act as the water dissociation promoter and the hydrogen recombination center, which synergistically propel water adsorption/dissociation and H intermediates recombination. The resulting synergistic interfaces between VPO and Ni2P are verified to afford the catalyst an outstanding performance for hydrogen evolution reaction in alkaline media with an overpotential of 154 mV at 10 mA cm−2, Tafel slope of 65 mV dec−1, and remarkable durability. Furthermore, the catalyst presents the potential for overall water splitting. This work may shed fresh light on the high-performance electrocatalyst design and the application of VPO on water electrolysis.

A Single-Event MicroKinetic (SEMK) model has been extended towards the simulation of Steady State Isotopic Transient Kinetic Analysis (SSITKA) data for Co catalyzed Fischer-Tropsch Synthesis (FTS). The extended model considers two types of sites and both direct and H-assisted CO dissociation. Regression of the model parameters to the data obtained from 17 steady state and 11 SSITKA experiments resulted in physicochemically meaningful estimates for the activation energies and atomic chemisorption enthalpies. The application of the phenomenological UBI-QEP method allows to physically interpret the nature of the two site types considered in the model, i.e., terrace and step sites. A reaction path analysis shows that over 80 percent of the CO reacts on the step sites. Furthermore, chain growth exclusively occurs on these sites. The terrace sites are less reactive for CO dissociation and are identified as responsible for methane production. A fraction of the alkenes, produced on the step sites, is hydrogenated to alkanes on the terrace sites. Based on model simulations, the metal particle size effect, i.e., a lower TOF, higher methane selectivity and increasing alkane to alkene ratio with decreasing metal particle size, is attributed to an increasing relative importance of the terrace sites on the reaction kinetics.

The first-order phase transition plays a pivotal role in material behaviors, yet that of carbides, a type of important materials, has not been systematically studied. Herein, the melting process and structural properties of binary iron carbide (FexCy) nanoparticles are characterized by reactive molecular dynamics simulation. It was found that the melting point of FexCy nanoparticle decreased with decreasing size and increased with increasing Fe/C ratio, which were consistent with the experimental results. The melting process starts at the surface and proceeds inwards. The carbon atoms are fully activated before reaching the melting point and the iron core melts last. At high temperatures, carbon atoms exhibit significant outward diffusion behavior and form carbon deposition on the surface. When the temperature exceeds the pre-melting point, although the high temperature gives the nanoparticles more atomic active sites with low coordination, the surface carbon accumulation, such as C2, blocks the active sites leading to a lower turn-over frequency of FexCy for CO dissociation. These findings provide an atomistic comprehension of the melting mechanisms and behaviors of binary FexCy nanoparticles, as well as a theoretical foundation for understanding their structural transformation as a catalyst, which is caused by the heat released from catalytic exothermic reactions.

A simplified computational scheme for “deposition” of a metallic (Pd) monolayer on semi-ionic supports is considered. An arbitrary selection of the initial position of the deposited layer relative to the surface of the support cannot provide the best solution for an optimal atom–atom binding. The energy and/or geometry changes were checked relative to a slide of the mono- and bilayers in parallel to the support layer and re-optimization. Two types of possible consequences are shown at the slide length of 1–3 A for γ-Al2O3(110), monoclinic ZrO2(001) (or m-ZrO2), and rutile TiO2(001) (or TiO2 below). First consequence option: either the Pd monolayer completely collapses after the shift/optimization, or it yields a new geometry (at γ-Al2O3(110) and m-ZrO2) at different steps. Second consequence option: the shift leads to a loss of the Pd stabilization while the ordered monolayer's geometry is retained (at TiO2 and m-ZrO2). The extent of such destabilization varies depending on the strength of the interaction with the support. It is thus recommended to verify Pd stabilization energy by sliding/optimizing the monolayer along one or two monolayer directions in order to avoid its energy underestimation. The activity of such monolayers for modelling catalysis is demonstrated using H2O dissociation in the Pd monolayer/rutile system.

In this work, we have performed density functional theory (DFT) calculations to investigate the methanol electro-oxidation reaction (MOR) catalyzed by the Pt, PtCu alloy and Cu. The complex reaction networks, including the intermediate dehydrogenation, water dissociation and anti-poison reaction steps, are systematically investigated to explore the mechanisms. At the standard condition of pH = 0 and zero potential, for Cu, most dehydrogenation steps along the favorable pathway are endergonic, making it less active in MOR. For the Pt and PtCu alloy, their dehydrogenation steps are mainly exergonic, but the formed CO intermediate binds too tightly on Pt, that can accumulate on active sites to poison the electro-catalyst. The CO can be consumed by the thermodynamic reaction with OH*, which comes from water dissociation. DFT calculation shows alloying the Pt with Cu could not only reduce the free energy barrier for binding between CO* and OH*, but also assist the water dissociation to produce more OH* for that anti-poison reaction. That makes the PtCu alloy more active than the pure Pt electrode in experiment. The results reveal the importance of anti-poison reaction and water dissociation in MOR, which could be applied to the rational design of more active alloy electro-catalysts in future.

How to utilize inexhaustible solar light as a means of disinfection technology for its cheap and green remains a challenge. In this work, core-shell ZnO@ZIF-8 was synthesized and used for bacterial inactivation synergizing with peroxymonosulfate (PMS) under visible light irradiation. It took 50 min to achieve thorough sterilization for 7.5-log {\it{Escherichia coli (E. coli)}} cells in vis/PMS/ZnO@ZIF-8 system, compared with that 4.5-log reduction completed in Vis/PMS/ZnO system under the same conditions. The enhanced photocatalytic disinfection mechanisms of fabricated ZnO@ZIF-8 were investigated by UV–vis diffuse reflectance spectra, electrochemical impedance spectra and Mott-Schottky plots. The promoted bactericidal efficiency was attributed to higher charge-separation efficiency and stronger oxidation ability of photo-generated holes. Moreover, it was found that 1O2 and •OH induced bacterial cell lesion process, and the former was the main active species. The external reactive oxygen species (ROS) caused a series of cell wall damage, intercellular ROS up-regulation and genome DNA unwinding, finally resulted in irreversible bacterial death. A two-route mechanism in vis/PMS/ZnO@ZIF-8 system was proposed, in which the generation of 1O2 was supposed as the product of the oxygen oxidation of photo-generated holes and PMS dissociation. Our work is expected to provide advanced information about a low-cost water disinfection technology of visible light photocatalysis.

Fabricating heterostructures with dense interfacial catalytic sites is vitally essential for implementation of high-performance hydrogen evolution reaction (HER). However, the strong correlation between the adsorbed hydrogen atoms and electronegative nonmetal atoms gives rise to the unfavorable hydrogen desorption behavior on heterointerface, especially on the metal sulfides heterointerface, which severely restricts the alkaline Volmer and Heyrovsky reaction kinetics. Herein, we present a simple way to incorporate nitrogen into the NiS2/CoS2 heterostructure (N-NiS2/CoS2) to form an electron-reconfigured heterointerface. The electronic structure of active sites on N-NiS2/CoS2 interface can be effectively tuned by N dopant, thus realizing a promoted water adsorption and dissociation capability, and near-optimal hydrogen desorption behavior on N-NiS2/CoS2 interface. Consequently, the as-prepared N-NiS2/CoS2 heterointerface demonstrates an impressive HER performance with a low overpotential of 73 mV at the current density of 10 mA cm-2 and a small Tafel slope of 64.8 mV dec-1. This work sheds light on the strategies of element doping on interfacial engineering HER, and also provides valuable insights for rational design of a high-performance heterointerface electrocatalyst.

To understand the microscopic mechanism of the CO oxidation reaction at PtCu nanoparticles, which have unique geometric and electronic structures compared to their component metals, we present here a theoretical study, based on density functional theory calculations, of the main reaction steps of this reaction. We examine the O2 dissociation, the CO adsorption and the CO + O2 reaction at an atomic level and use the computed geometries, Bader charges, and vibrational frequencies to rationalize the role of the intermetallic nanoparticles surface structure on the experimentally observed much higher activity of these nanoparticles as catalysts of the preferential oxidation of CO. By comparing with clean Pt (111) surface and with different Cu-doped models of this same surface, our results show that, at the surface, the presence of Cu induces the segregation of CO molecules at Pt sites and of O2 molecules at Cu sites. Contrarily to Pt surfaces, the unassisted O2 dissociation has a high barrier at the intermetallic nanoparticle surface and proceeds through a CO-assisted mechanism in which the new CO bond is formed while the O O bond is broken with a kinetic barrier much lower than on either Pt (111) or in Pt-doped surfaces. The particular structure of the intermetallic surface is shown to have a significant role in the low kinetic barrier for the reaction, allowing for an easy approach of the CO to the adsorbed O2 molecule that permits an early transition state with a low energetic barrier.

Significant efforts have been directed towards the use of transition metal nitrides as electrocatalysts for hydrogen evolution reaction (HER). Molybdenum nitride, despite its promise for scalable production, suffers from the bottleneck of poor catalytic activity. Furthermore the kinetics of water dissociation process ought to be improved for enhancing its potential. Here, we report a facile method for the incorporation of trace amount of Pd nanoparticle into Mo3N2 nanobelts (0.75Pd/Mo3N2,) for enhanced HER in both acidic and alkaline solutions. When employed for HER, the 0.75 wt%Pd/Mo3N2 nanobelt delivers excellent catalytic activity with overpotentials of 45 and65 mV in 0.5 M H2SO4 and 1 M KOH at a current density of 10 mA cm-2. As-prepared 0.75 wt%Pd/Mo3N2 displays a smaller Tafel slope and offers substantial stability in both acidic and alkaline media under the same operating conditions. The improved performance of the as-prepared 0.75 wt%Pd/Mo3N2 points to fast charge transfer, higher electrical conductivity and synergistic effects between Pd and Mo. This work displays a direct method for reducing the use and cost associated with use of platinum-group metals while also delivering superior HER catalytic performance.

Exploring the initial reactions of H-free and nitro-free energetic materials could enrich our understanding into the thermal decomposition mechanism of various energetic materials (EMs). In this work, two furoxan compounds, 3,4-dinitrofurazanfuroxan (DNTF) and benzotrifuroxan (BTF), were investigated to shed light on the decay mechanism of furoxan compounds based on the self-consistent charge density functional tight binding molecular dynamic simulations. Results show that DNTF and BTF decay in a unimolecular mechanism, and the transformation of furoxan ring to nitro group are suggested as a novel initial channel. Five initial steps of DNTF are observed, including NO2 loss and the N(O)-O bond cleavage of central and peripheral rings. The bond cleavage of peripheral rings dominates the decay at low temperature, while the central ring opening and C-NO2 dissociation governs the high temperature decay. Besides, NO2, CO and NO fragments are mainly yield at high temperature, while CO3N2 is dominant at low temperature. The three-stage characteristics of the exothermic of BTF decay are described under programmed heating conditions for the first time. Four initial steps of BTF were identified, including furoxan ring opening reactions and the breakage of 6-membered ring C-C bond. The cleavage of N(O)-O bond rules the initial step of BTF under different heating conditions, and the frequency increased with the temperature increasing. In addition, the amount of CON, ON and CO are higher at high temperature, while C2O2N2 shows a opposite trend. What obtained this work promote deepen insights into the complicated sensitivity mechanism of EMs.

Hydrogen evolution from electrochemical water splitting under alkaline conditions is an ongoing challenge for the requirement of a simultaneous balance to be achieved between the water dissociation step and the hydrogen adsorption on the catalysts. Herein, Bi2O3, an inactive catalyst for hydrogen evolution reaction (HER) aroused by its unfavourable hydrogen adsorption Gibbs free energy (ΔGH*), is activated by an in-situ phase engineering strategy for efficient HER electrocatalysis in alkaline media. Via this strategy, two-dimensional (2D) dual active Bi2O3 nanosheets with both BixNi alloy phases and α-Bi2O3 were fabricated to simultaneously catalyse the water dissociation step and the hydrogen formation step during the alkaline HER. In combining with the advantages of 2D nanomaterials and dual active catalytic sites, this phase engineered Bi2O3-based catalyst exhibited simultaneously accelerated water dissociation and optimized ΔGH* and thus excellent HER performance. The modulated catalyst demonstrated an overpotential of 127 mV (at j = 10 mA cm-2) and a Tafel slope of 92 mV dec-1 in 1 M KOH, which is exceptional compared with other Bi2O3-based HER electrocatalysts. This work not only provides an innovative way to activate HER-inferior bismuth oxide-based catalysts, but also offers new insights into the design of dual active catalysts for sluggish alkaline HER catalysis.