Atomic-level insight into the carburization process of iron-based catalysts: A ReaxFF molecular dynamics study

Exploring carbon dioxide generation in combustion of long-flame coal in Huating mining area by using ReaxFF MD

To investigate the antioxidant mechanisms of phenolic antioxidants in base oils, this study employed the reactive force field (ReaxFF) molecular dynamics (MD) simulations to reveal the reaction pathways and product distributions of trihydroxymethylpropyl trioleate (TMPTO, base oil) and antioxidants AO-80 and XH-245 under high-temperature conditions. A multi-output regression prediction model (MORP) was developed to achieve accurate prediction of carbon atom types and chemical bond types in the reaction systems. Furthermore, a chemical reaction prediction model (CRPM) based on graph neural networks (GNN) was developed to predict the product types and distributions at different times during the antioxidant process of lubricating oils. The results show that the oxidative decomposition of TMPTO is characterised by the cleavage of C–C bonds and C–O bonds. The main small-molecule oxidation products include CO2, C2H4, H2O, CO, formaldehyde, formic acid, and other C2 and C3 compounds. The ArOH groups in phenolic antioxidant molecules can delay the oxidative cleavage process of base oil through hydrogen transfer steps. The system with the two types of antioxidants exhibits better antioxidant effects than the single antioxidant system under the same conditions. The MORP and CRPM models provide good prediction results for carbon atom types, chemical bond types, and product distributions.

Effect of Fe and its oxides on steam gasification mechanism of lignin using ReaxFF molecular dynamics simulations

Initiation mechanisms of enhanced pyrolysis and oxidation of JP-10 (exo-tetrahydrodicyclopentadiene) on functionalized graphene sheets: Insights from ReaxFF molecular dynamics simulations

Reactive force field (ReaxFF) molecular dynamics investigation of bituminous coal combustion under oxygen-deficient conditions

Algorithms of GPU-enabled reactive force field (ReaxFF) molecular dynamics

Nitramine compounds are typical high-energy-density materials (HEDMs) and are widely used as explosives because of their superior explosive performance over conventional energetic materials. In this work, the thermal properties of 1-nitropiperidine (NPIP), 1,4-dinitropiperazine (DNP), and 1,3,5-trinitro-1,3,5-triazinane (RDX) were investigated from quantum mechanics (QM) and reactive force field (ReaxFF) molecular dynamics simulations. We found that the bond dissociation energy of the N-NO2 bond, heat of formation, released energy, produced fragments, and oxygen balance are closely related to the incremental nitramine group. The nitramine group has a significant effect on the energetic performance of these nitramine compounds. In addition, the increase of the nitramine group will improve thermal decomposition activity, promote the generation of small molecules, and restrain the formation of carbon clusters. We hope that this work can shed new light on the design of energetic materials.

This work presents a dynamic and kinetic study on the dimerization of polycyclic aromatic hydrocarbon (PAH) molecules and radicals under flame conditions using reactive force field (ReaxFF) molecular dynamics (MD) simulations. The accuracy of the ReaxFF force field is evaluated through comparing with quantum chemistry (QC) calculations of the barrier heights and species concentrations of PAHs reacting with H and OH radicals. A series of homobinary collisions between PAH molecules/radicals are performed to reveal the influence of temperature, molecular size, PAH composition, and the number of radical sites on the dynamics and kinetics of PAH dimerization. Instead of directly forming the strong covalent bonds, the majority of the binary collisions between PAH radicals are bound with weak intermolecular interactions. Effects of oxygen on PAH radical dimerization are also investigated, which indicates that the oxygenated PAH radicals are less likely to contribute to soot nucleation. In addition, thetemperature, PAH characteristic, and radical site dependent collision efficiency for PAH radical-radical combinations isextracted from this study.

We explore here, through reactive force field (ReaxFF) molecular dynamics simulations, oleic acid upgrading on beta zeolite (BEA) regulated with nine silica-to-aluminium ratios (SARs) to investigate their acid-catalyzed deoxygenation and coking susceptibility. The selected computational descriptors involved conversion, hydrodeoxygenation, and decarboxylation/decarbonylation selectivity, biofuels yield, and coke deposition characteristics. Simulations were validated by 20.3 SAR available experimental data and used for the systematic study. High deoxygenation selectivity was found to be related to the structural sensitivity of BEA(100) on the upgrading mechanism. ReaxFF simulations revealed that altering the Al-substitution could greatly promote biofuel formation. Specifically, SARs towards the mid-region (SAR 47) favored gasoline production, while 31 SAR exploited diesel-like hydrocarbons. An optimum ratio of 37.4 SAR achieved maximum oleic acid conversion (69.8%), with high yields of gasoline and diesel fuels (15.6 and 20.4 wt%, respectively) and moderate coking (8.6 wt%). Density functional theory screening of metallic dopants allowed investigating of their deoxygenation and coke susceptibility, obtaining that Cu-BEA structure favored the optimal carbon and O-moiety adsorption (-3.89 and -1.8 eV, respectively). Furthermore, the economic and environmental analysis showed that Cu-dopped BEA displayed the lowest market price and global warming potential (71 USD/kg and 2.8 kg CO2-eq/kg).

Thermal decomposition of vegetable insulating oils from reactive molecular dynamics

Theoretical study of the CO formation mechanism in the CO2 gasification of lignite

In this study, we employed the advanced reactive force field (ReaxFF) molecular dynamics (MD) simulations to investigate the adsorption mechanisms of acetone, ethanol, methanol and propanol molecules on newly-designed tubular helix nanostructure doped by sulfur substituting carbon atoms. The adsorption processes of four different volatile organic compounds (VOCs) on tubular helix nanostructure are simulated at temperature of 300 K, containing fixed 100 adsorbate molecules. The adsorption energy of acetone is calculated as -4.4 eV which is higher than that of other molecules and it exhibits very strong adsorption of acetone on active sites of tubular helix nanostructure attracting this molecule. Moreover, some MD structural analysis methods, such as partial correlation function (PCF) and diffusion coefficients from mean square displacement (MSD) reveal that O atom in acetone molecule strongly interactions with C and S atoms on tubular helix nanostructure in short distance of 1.17 Å. Addition, the diffusion coefficient of acetone molecule into tubular helix nanostructure is more than that of other molecules indicating faster and easier movement in helical environment. Finally, molecular entrapment capability of tubular helix nanostructure and the surrounding level of acetone molecules the tubular helix nanostructure were revealed by computational method. The computational results help understand the great potential of gas sensor device of newly-designed tubular helix nanostructure in the context of pioneer experimental studies.

In this work, we present the parametrization of Ca-O/H interactions within the reactive force field ReaxFF, and its application to study the hydration of calcium oxide surface. The force field has been fitted using density functional theory calculations on gas phase calcium-water clusters, calcium oxide bulk and surface properties, calcium hydroxide, bcc and fcc Ca, and proton transfer reactions in the presence of calcium. Then, the reactive force field has been used to study the hydration of the calcium oxide {001} surface with different water contents. Calcium oxide is used as a catalyzer in many applications such as CO(2) sequestration and biodiesel production, and the degree of surface hydroxylation is a key factor in its catalytic performance. The results show that the water dissociates very fast on CaO {001} bare surfaces without any defect or vacancy. The surface structure is maintained up to a certain amount of water, after which the surface undergoes a structural rearrangement, becoming a disordered calcium hydroxyl layer. This transformation is the most probable reason for the CaO catalytic activity decrease.

Elucidating the role of extended surface defects at Fe surfaces on CO adsorption and dissociation

The interaction of water molecules on a nickel surface was studied using ReaxFF (reactive force field) molecular dynamics. This approach was originally developed by van Duin et al. to study the hydrocarbon chemistry and the catalytic properties of organic compounds. To our knowledge, this method has not been used to study the corrosion processes of nickel exposed to water, which is what we set out to achieve in the present investigation. To do so, calculations were first performed using ReaxFF in order to reproduce certain well-known properties of pure nickel and nickel-water systems. This allowed us to study the adsorption of a single water molecule interacting with an optimized nickel surface. We also investigated the interaction of 405 molecules of water (ρ=0.99 g.cm-3) on the (100), (110) and (111) surfaces of a single crystal of nickel at 300 K. The results show that a water bilayer is adsorbed on nickel surfaces: the first water layer is directly bonded to the surface, whereas the molecules in the first and second layers are held together by hydrogen bonds.