Atm Pressure Research Articles

Room‐Temperature Reversible Hydrogen Storage in Scandium‐Decorated [6]Cycloparaphenylene: Computational Insights

ABSTRACTThis study discusses the hydrogen storage and delivery capacity of Sc‐decorated [6]cycloparaphenylene ([6]CPP) using dispersion‐corrected density functional theory calculations (DFT + D3). The scandium atoms are decorated over [6]CPP via Dewar coordination with an average binding energy of 1.33 eV. Each Sc atom stores up to 5H2 molecules in quasi‐molecular form at an average adsorption energy ranging from 0.23 to 0.36 eV/H2. The system's stability before and after H2 adsorption is checked using reactivity parameters. The maximum hydrogen gravimetric capacity of the system is found to be 7.68 wt% at low temperatures at 1–60 bar pressure. With an increase in temperature (300–420 K), the gravimetric density is more than 5.5 wt% (US‐DOE target) below 60 bar. Atom‐Centered Density Matrix Propagation (ADMP)‐molecular dynamics (MD) simulations reveal that the desorption of H2 molecules from [6]CPP starts at around 300 K/1 bar, and complete desorption occurs above 480 K. The minimum Van't Hoff desorption temperature for [6]CPP‐Sc is 296.9 K at 1 atm pressure. Insignificant change in the structure of [6]CPP‐Sc during adsorption and desorption processes promises stability and reversibility of the system. Hence, we believe that Sc‐decorated [6]CPP can be a promising candidate for hydrogen storage applications.

Adsorption-absorption technique for effective CO2 capture

ABSTRACT This paper presents a study on the removal of CO2 gas from gas mixture (CO2/N2) of 14% CO2 using adsorption onto zeolite 13X in a fluidized bed at 298 K and 1 atm pressure. The effects of static bed height (5–25 cm) and rate of flow of the gas mixture (6–14 L/min) on the breakthrough time were studied. The desorption of CO2 was performed by absorbing the adsorbed CO2 molecules using NaOH solution (0.1 M). The absorption process which was accompanied with chemical reaction achieved two objectives. The first was converting CO2 gas into a valuable substance (Na2CO3) which could be used in many industries. The second was the storage of CO2 gas in what was called a chemical carrier which could emit the gas when it was needed. The effect of static bed height (5–25 cm) on the absorption process in the fluidized bed was also studied. For the adsorption process, the results showed that the breakthrough time increased with decreasing the flow rate but with increasing the static bed height. In the desorption process, the total amount of absorbed CO2 molecules was 396 mg, achieving a recovery of 90.8% at 5 cm static bed height.

Theoretical Kinetics of Radical-Radical Reaction NH2ṄH + ṄH2 and Its Implications for Monomethylhydrazine Pyrolysis Mechanism.

Significant discrepancies were observed between the experiments and the simulations for ṄH2 time-histories in monomethylhydrazine pyrolysis with the robust mechanism proposed by Pascal and Catoire. The rate of formation analyses for ṄH2 indicated the significance of the reaction NH2ṄH + ṄH2 = H2NN + NH3, which has not been well-defined. In this study, ab initio calculations were performed for the theoretical description of the NH2ṄH + ṄH2 chemistry. Most stationary points on the potential energy surface were quantified at the CCSD(T)/CBS//M06-2X/aug-cc-pVTZ level, and the multireference methods were employed for barrier-less reaction and some transition states. The temperature- and pressure-dependent rate coefficients were determined using classical and microcanonical variational transition state theories. Four primary reaction channels were identified as competitive: 1) The H atom abstraction reaction yielding N2H2(T) + NH3, dominating at 1350-3000 K across the 0.001-100 atm pressure range. 2) The H atom abstraction reaction forming N2H2(S) + NH3, dominating at 800-1350 K and competing with the processes of chemical activation and collisional stabilization below 800 K. 3) The chemical-activated reaction resulting in H2NN(S) + NH3, dominating below 800 K at 0.001 atm. 4) The collisional-stabilized recombination reaction leading to N3H5, becoming significant as pressure increases and dominating below 600 and 650 K at 1 and 100 atm, respectively. The implications of newly calculated NH2ṄH + ṄH2 kinetics for the monomethylhydrazine pyrolysis mechanism were evaluated, and updates were implemented. Sensitivity analyses indicated the necessity of additional research efforts to comprehend the dynamics of CH3NH2 unimolecular and N2H2 + ṄH2 reaction systems. The rate coefficients presented in this study can be employed to develop the chemical kinetic model of nitryl-containing systems.

Long-term hypothermic storage of oocytes of the European common frog Rana temporaria at various pressure regimes in gas mixtures based on oxygen, carbon monoxide, and nitrous oxide

In recent years, the challenge of preserving amphibian biodiversity has increasingly been addressed through technologies for the short-term storage of unfertilized spawn at low positive temperatures. Previously the possibility of using a 6.5 atm gaseous mixture of carbon monoxide and oxygen for prolonged hypothermic preservation of unfertilized oocytes for more than 4 days was shown. This study aimed to investigate the viability of oocytes R. temporaria preserved under conditions of hypothermia at 2.5, 3 and 6.5 excess atm pressure in the various gas mixture compositions (CO, N2O, O2) and pure oxygen. The use of pressure up to 3 excess atmospheres was significantly beneficial compared to 6.5 atm at the 7 days storage period. The results indicate that oxygen pressure is a critical factor in maintaining oocyte viability. Admixing CO or N2O to oxygen reduced variability in the results but did not significantly affect the measured indicators (fertilization, hatching) in the experimental groups. The composition CO + O2 (0.5/3.5 ratio, 3 excess atm) reliably extended the shelf life of viable oocytes, indistinguishable from native controls by fertilization and hatching rates, to 4 days. After 7 days, oocytes exhibited fertilization and hatching rates that were 79 % and 48 % compared to native control. Reducing the pressure of the preserving gas mixture to 3 atm, as utilized in this study, simplifies the practical implementation of gas preservation technology for maintaining endangered amphibian species during breeding in laboratory conditions.

Thermal Safety Study of Emulsion Explosive Matrix under the Coupled Effects of Environmental Pressure and Bubble Content with Internal Heat Source

Emulsion explosives have become a hot topic in various studies due to their explosive combustion characteristics and detonation performance under different environmental pressures. The thermal safety of an emulsified matrix was studied with ignition energy as the characterization. A minimum ignition energy test experimental system for emulsion matrices was established in this research. The system simulated the occurrence of hot spots inside emulsion matrices using an electric heating wire. The effect of bubbles on the thermal safety of the emulsified matrix was studied by adding expanded perlite additive to the emulsified matrix. This study investigated the variation trend in the minimum ignition energy of the emulsion matrix under the coupled effect of bubbles and ambient pressure using the orthogonal experimental method. The impacts of two factors on the thermal safety of the emulsion matrix were studied at different hot-spot temperatures. Coupled analysis experiments were conducted on emulsion matrices containing 0%, 1.5%, and 3% expanded perlite under pressure environments of 1 atm, 2 atm, and 3 atm. The critical hot-spot temperature of the emulsion matrix significantly decreases with increasing bubble content at 1 atm and 2 atm pressures, as revealed by intuitive analysis and analysis of variance. However, at 3 atm of pressure, the bubble content in the emulsion matrix has no significant effect on its critical hot-spot temperature. The results show that the thermal safety of the emulsified matrix decreases with the increase in the content of expanded perlite and environmental pressure, and the influence of environmental pressure is more significant than that of the bubble content. This paper’s research content serves as a reference for a safe emulsified matrix and as an experimental basis for establishing a production line for developing new equipment.

Investigating the potential of NH2-Functionalized MIL-53(Fe) nanoparticle as a carrier for 5-fluorouracil through molecular dynamics simulation

This study investigates the role of the NH2-functionalized MIL-53(Fe) nanoparticle as a carrier for the anti-cancer drug 5-fluorouracil (5-Fu) through molecular dynamics (MD) simulation. The Atom in Molecules (AIM) method was used to determine the interaction type between 5-Fu and NH2-MIL-53(Fe). The Steered Molecular Dynamics (SMD) approach was employed to calculate the free energy of drug encapsulation. The simulation included the NH2-MIL-53(Fe) nanoparticle containing 5-FU molecules and water molecules at different temperatures and 1 atm pressure. The properties analyzed included density, radial distribution functions, displacement, diffusion, and binding energy of the drug with NH2-MIL-55(Fe). It is shown that the drug was encapsulated in the framework channels and the variation of density of the system with temperature in the presence of nanoparticles decreased. The drug's mean square displacement, total self-diffusion coefficient, and diffusion coefficient in channel direction increased with time as temperature rose. The drug was aligned to have its oxygen atoms towards the metal nodes of the framework. However, The nitrogen atom of the amine functional group in NH2-MIL-53(Fe) interacts more with the F atom of 5-Fu which shows the effect of this functional group on the adsorption of the 5-Fu. The drug's adsorption percentage increased from 298 K to 328 K. The calculated binding energy increased with temperatures and was desirable as it countered the drug's repulsive forces with atoms of NH2-MIL-53(Fe). The results of the molecular docking simulation confirmed MD simulation.

Study of dual osmium and boron co-doped SWCNTs for reversible hydrogen storage

The dual osmium/boron doped/co-doped armchair single walled carbon nanotubes (SWCNTs) have been explored for hydrogen storage applications via ab-initio method. We thoroughly screen dual osmium/boron doping at two different opposite positions in SWCNTs and analyze bond distances, binding energy, band gaps, electrophilicity, density of states, adsorption energies, adsorption enthalpy, Gibbs free energy and storage capacity. The results summit Osmium doped CNTs as hopeful nominees for hydrogen storage applications. The findings indicates that Osmium atoms doping in opposite sides of CNT along with boron atoms at ortho position (2Os-2BCNT) show 1.95 wt% gravimetric hydrogen storage capacity at 298.15 Kelvin temperature and 1 atm pressure. Furthermore, the feasibility of doped SWCNTs have been explored for storage applications by performing average Van't Hoff desorption temperature calculations and molecular dynamics simulations for 2Os-2BCNT at maximum desorption temperature and 1 atm pressure.

Theoretical and Molecular Dynamics Simulation Approaches to Praseodymium Content Effect on Radiation Shielding and Time Dependent Volume‐Collapse for a Newly Produced Borate Glass

AbstractGamma‐ray, fast neutron and charged particle shielding characteristics of Praseodymium (Pr3+) activated glasses with composition 10ZnF2‐(10‐x)SrO‐15Li2O‐65H3BO3‐xPr2O3(where x = 0.1, 0.5, 1.0, 1.5, and 2.0) are investigated. For this, the radiation shielding parameters are estimated by using Photon Shielding and Dosimetry (Phy‐X/PSD), Interaction of Proton, Alpha, Gamma rays, Electrons, and X‐rays with matter (PAGEX), Stopping Powers and Ranges for Electrons (ESTAR), and The Stopping and Range of Ions in Matter (SRIM) codes. Furthermore, the results are compared comprehensively and comparatively. The glasses with increasing Pr3+ content exhibited higher shielding potential. It can be said that the ZFLHBPr2.0 sample could be used as a shielding material in various applied fields. Additionally, the effect of Pr composition on structural transitions and time‐dependent volume‐collapse of this new family of borate glass doped with Pr is analyzed by molecular dynamics study (MD) based density functional tight binding method. The simulation results show that the addition of Pr led to the cubic‐orthorhombic transformation of simulation cell at determined temperature and 1 atm pressure. Also, a sudden decrease in volume are observed within a short time at 8% Pr composition (x = 2.0) atmospheric pressure. This result provides a strong connection between Pr composition and volume change with time and at constant low pressure.

Investigating the Atmospheric Fate and Kinetics of OH Radical-Initiated Oxidation Reactions for Epoxybutane Isomers: Theoretical Insight.

Epoxides, which belong to the category of oxygenated volatile organic compounds (OVOCs), are emitted into the atmosphere by an array of sources and can impact both human and environmental well-being significantly. This study involves comprehensive computational analyses aimed at investigating the mechanism, thermodynamic aspects, and reaction kinetics associated with hydrogen abstraction reactions of cis-2,3-epoxybutane, trans-2,3-epoxybutane, and 1,2-epoxybutane by OH radicals. The potential energy diagrams involving all of the species for each specific pathway were constructed at the CCSD(T)/aug-cc-pVTZ//M06-2X/cc-pVTZ level of theory. The rate coefficients for all possible pathways were calculated using the Rice-Ramsperger-Kassel-Marcus master equation (RRKM-ME) corrected by Eckart tunneling within the 200-350 K temperature range and 1 atm pressure. The overall rate coefficients of the reaction of cis-2,3-epoxybutane, trans-2,3-epoxybutane, and 1,2-epoxybutane with OH radicals at 298.15 K were found to be 0.32 × 10-12, 0.33 × 10-12, and 0.66 × 10-12 cm3 molecule-1 s-1, respectively. We also studied the atmospheric lifetime and photochemical ozone creation potential (POCP) of all three compounds. In addition, we have provided extensive degradation pathways for the product radicals formed from the initial reaction with OH radicals in the presence of O2 and NO. The study showed that the product radicals can result in various harmful end products, including grade 1 and grade 2 carcinogens, as listed by the World Health Organization (WHO).

Fabrication of polysulfone-cellulose acetate based TiO2 @SiO2-CuS and Fe3O4 @XG membrane and its application in wastewater treatment

Membrane technology emerged as a preferred method for wastewater treatment due to its efficiency, and low energy consumption, particularly in pharmaceutical industries. In this study, two types of membranes were developed and compared: cellulose acetate with dimethyl sulfoxide, glycerol, and polysulfone with dimethylformamide, and polyvinyl pyrrolidone. These membranes were augmented with nanocomposites, such as Fe3O4 @XG and TiO2 @SiO2-CuS, to enhance performance. Experimental investigations involved doping membranes with nanocomposites at varying concentrations (0.1 wt%, 0.5 wt%, and 1.0 wt%). Atomic force microscopy revealed that increasing nanocomposite content led to smoother surfaces and improved anti-fouling properties. Incorporating nanocomposites reduced the contact angle, with 1.0 wt% PSF/TiO2 @SiO2-CuS exhibiting the lowest angle at 33.134°. Physical property assessments, including density, viscosity, pH, and porosity, were conducted to evaluate the impact of nanocomposites. Under 4 atm pressure, 1.0 wt% CA-TiO2 @SiO2-CuS demonstrated a maximum pure water flux of 3300 ± 50 lit/m2.hr compared to the pure membrane. Furthermore, biodegradability tests indicated a significant weight loss of the nanocomposite membranes, with a 13.89 % increase in CA membrane weight loss compared to a 0.20 % increase in PSF membrane weight loss. The study highlights the potential of these membranes for diverse applications, particularly in wastewater treatment, underscoring their efficiency and suitability for pharmaceutical industry use.

Experimental and theoretical thermal performance analysis of additively manufactured polymer vacuum insulation panels

Vacuum Insulation Panels (VIPs) are characterized by low thermal conductivity, which makes them attractive for applications in buildings, refrigerators, and cold chain logistics. The study of new technologies to manufacture VIPs has grown considerably in recent years. This work presents a feasibility analysis of additive manufacturing technique to manufacture polymer VIPs. The 3D printable multilayered VIPs, in which several interlayers are utilized to suppress gas conduction and thermal radiation, are designed and then manufactured using a commercial fused deposition modeling 3D printer. The effective thermal conductivity of the 3D printed VIPs is evaluated at various vacuum levels (1 atm, 10,000 Pa, 1000 Pa, 100 Pa and 10 Pa) using the standard test method (ASTM C518). Additionally, an analytical model and numerical simulation are performed to analyze heat transfer in these 3D printed VIPs and optimize the VIP design. The experimental results show that an effective thermal conductivity of 0.0155 W/m/K is achieved for the 3D printed VIP with 8 solid interlayers at 10 Pa, which is about 60 % of the thermal conductivity of air at 1 atm pressure. It is also found that there exists an optimal number of interlayers in the multilayered VIPs when its pressure is >1000 Pa. At lower pressures, the effective thermal conductivity of the multilayered VIPs decreases monotonically with increasing number of interlayers. This work is the first one to employ 3D printing techniques to manufacture polymer VIPs, and it is expected to offer a pathway for wider adoptions of VIPs due to its advantage low cost and high manufacturing flexibility.

Hydrogen adsorption, desorption, sensor and storage properties of Cu doped / decorated boron nitride nanocone materials: A density functional theory and molecular dynamic study

The hydrogen storage and sensor properties of Cu-modified boron nitride nanocone (BNNC) structure were comprehensively investigated using the density functional theory method (DFT). By replacing nitrogen atoms with copper atoms on the BNNC structure, the hydrogen molecule's adsorption enthalpy and Gibbs free energy values were calculated as −48.6 and −16.9 kJ/mol, respectively. 4 Cu-doped BNNC structure achieved a notable hydrogen storage capacity of 5.38 wt%. The molecular dynamics calculations demonstrate that the structure modified with four Cu atoms maintains its dynamic stability. Furthermore, this study reveals that the desorption temperatures tend to rise with an increase in the number of adsorbed hydrogen molecules, and the average desorption temperature under 1 atm pressure is determined to be 332 K. The changes of work function values after hydrogen adsorption point out that the Cu-modified BNNC has Φ-sensor feature. Overall, Cu-modified BNNC structures show promising potential as hydrogen storage materials in ambient conditions.

Structural characterization and keto-enol tautomerization of 4-substituted pyrazolone derivatives with DFT approach

The synthesis of two pyrazolone derivative compounds, PYR-I(4-Acetyl-1-(4-chlorophenyl)-3-isopropyl-1H-pyrazol-5(4H)-one) and PYR-II1-(4-Chlorophenyl))-3-isopropyl-5-oxo-4,5-5-dihydro-1H-pyrazole-4-carbaldehyde, their characterization by FT-IR, NMR, UV–Vis and GC-MS techniques, and the evaluation of the keto-enol tautomerization process of the structures along with the DFT approach and spectral data were reported in this paper. Spectral findings indicated that PYR-I was stable at the keto state. The IR spectrum recorded in solid form showed that the PYR-II structure was stable in the enol state, while the NMR spectrum in the solution medium showed that it was stable in the keto state. DFT-based analyses were realized with the B3LYP hybrid functional and the 6–311++G(d,p) basis set. The modelled keto, transition and enol state molecular geometries of structures were optimized in the gas phase and different solvent media and the total energy and dipole moment values were investigated at the specified theoretical level. The possible keto-enol tautomerism mechanism of the structures was evaluated through some thermodynamic parameters such as the difference in free Gibbs energy (ΔG), enthalpy (ΔH), entropy (ΔS), and predictive tautomeric equilibrium constants (Keq), acidity constants (pKa) and percentages of tautomers at 298.15 K and 1 atm pressure. The results of these analyses based on the DFT approach indicated that the keto-enol tautomer equilibrium heavily favours the keto form for PYR-I and the enol form for PYR-II in all cases. Moreover, natural bond orbital (NBO) analysis was performed for the tautomers, and the chemical reactivity profiles of the most stable tautomers were examined with the values of frontier molecular orbital energy and some reactivity descriptors.

Hydrogen Adsorption on Type-5 Penta-MgN8 Sheet, Nanotube, and 3D Porous Structure.

Motivated by the recent report on penta-MgN8 sheet [Mater. Today Phys. 2023, 38, 101259] that is the first realization of type-5 pentagonal 2D tessellation with exposed regularly distributed Mg ions, we carried out density functional theory studies on the interactions of H2 molecules with 1D penta-nanotube, 2D penta-sheet, and 3D porous structures based on penta-MgN8. We found that when the penta-MgN8 sheet is assembled to a 3D porous structure or curved to a nanotube, the bandgap increases from 1.18 to 1.35 and 1.88 eV, and the resulting derivatives are stable dynamically. When H2 molecules are introduced, the nanotube behaves best in adsorption, where each Mg ion can adsorb three H2 molecules: two on the outer surface and one on the inner surface. The curved geometry of the nanotube makes the Mg ion on the outer surface more exposed as compared with the situations of the 2D sheet and 3D porous structure, resulting in stronger adsorptions to H2. The gravimetric capacity (volumetric capacity) is 4.25 wt % (63 g/L) and 4.25 wt % (65 g/L) for the studied penta-sheet and penta-nanotube, and the corresponding desorption temperature is 115 and 162 K at 1 atm pressure, respectively, while for the 3D porous structure, the adsorption performance is poor due to the limited space and the less curvature, leading to strong steric hindrance and less exposed configuration for Mg ions. Moreover, the effects of temperature and pressure on adsorption are also discussed.

Quantum computational, charge density, optical, molecular reactivity and thermodynamical analysis of Di-Halogen substituted nicotinic acid derivatives

6-Chloro-3-fluoro-2-(trifluoromethyl) isonicotinic acid (6C3F2TINA) and 6-Chloro-5-fluoronicotinic acid (6C5FNA) are currently being studied using the DFT method for the detailed examination of structural and molecular character alterationsin gas as well as in several organic solvent media. Implementing electrostatic potential maps and Fukui functions analyses the reactive environment of compounds. The occurrence of the transfer of electrons and holes within the molecule is reported by a charge transfer study along with the heat maps. The orbital study investigates the electronic density and interactions within themolecules. Optical examination of compounds revealed an enhancement with the solvents. Thebonding typefound in molecules isdetermined by topographical investigation, which examines the concentration and localisationof electrons present in them. The UV–Vis spectra exhibit the absorption characteristics of these compounds. The thermodynamic investigation reveals the compound’s stability at various temperatures at 1 atm pressure.

Comparison of the Snare Loop Technique and the Hungaroring Reinforcement for Physician-Modified Endograft Fenestrations-An In Vitro Study.

We conducted an in vitro comparison of the snare loop reinforcement against a closed-loop reinforcement (Hungaroring) for physician-modified endograft (PMEG) fenestrations regarding preparation time and stability during flaring balloon dilatation. The time to complete a PMEG fenestration with reinforcement was measured and compared between the Hungaroring and snare loop groups. The number of stitches was counted. Each fenestration was dilated using a 10 mm high-pressure, non-compliant balloon up to 21 atm in pressure, and fluoroscopic images were taken. The presence of indentation on the oversized balloon at the level of the reinforcement was evaluated at each fenestration. Five fenestrations were created in each group (n = 5) for a total of ten pieces. The completion time in the snare loop group was 1070 s (IQR:1010-1090) compared to 760 s (IQR:685-784) in the Hungaroring group (p = 0.008). Faster completion time was achieved by faster stitching (23.2 s/stitch (IQR 22.8-27.3) for the snare loop group and 17.3 s/stitch (IQR 17.3-20.1) for the Hungaroring group (p = 0.016). None of the fluoroscopic images of the snare loop reinforcement showed an indentation on the balloon during the overexpansion; on the contrary, the Hungaroring showed indentation in every case, even at 21 atm. Fenestrations reinforced with Hungaroring can be completed significantly faster. Furthermore, the Hungaroring resists over-dilation even at high pressures, while snare loop reinforcements dilate at nominal pressure.

Growth of diamond in liquid metal at 1 atm pressure.

Natural diamonds were (and are) formed (thousands of million years ago) in the upper mantle of Earth in metallic melts at temperatures of 900-1,400 °C and at pressures of 5-6 GPa (refs. 1,2). Diamond is thermodynamically stable under high-pressure and high-temperature conditions as per the phase diagram of carbon3. Scientists at General Electric invented and used a high-pressure and high-temperature apparatus in 1955 to synthesize diamonds by using molten iron sulfide at about 7 GPa and 1,600 °C (refs. 4-6). There is an existing model that diamond can be grown using liquid metals only at both high pressure and high temperature7. Here we describe the growth of diamond crystals and polycrystalline diamond films with no seed particles using liquid metal but at 1 atm pressure and at 1,025 °C, breaking this pattern. Diamond grew in the subsurface of liquid metal composed of gallium, iron, nickel and silicon, by catalytic activation of methane and diffusion of carbon atoms into and within the subsurface regions. We found that the supersaturation of carbon in the liquid metal subsurface leads to the nucleation and growth of diamonds, with Si playing an important part in stabilizing tetravalently bonded carbon clusters that play a part in nucleation. Growth of (metastable) diamond in liquid metal at moderate temperature and 1 atm pressure opens many possibilities for further basic science studies and for the scaling of this type of growth.

Hydrogen storage properties of Ti-doped C20 nanocage and its derivatives: A comprehensive density functional theory investigation

We have innovatively designed and assessed the hydrogen storage properties of a single Ti-doped C20 nanocage and its B, N or B and N heteroatom substituted derivatives with the help of the density functional theory approach for the first time to the best of our knowledge. Out of fifteen designed structures by substituting heteroatoms, only 8 structures are found to be suitable for Ti doping and H2 adsorption viz. C20, C12N8, C12B8, C12B4N4, C10B5N5, C10B10, B10C10 and B10N10. Their formation energy and cohesive energy values confirm the stability of all the structures. Ti atom binds more strongly with B, N or B and N heteroatom substituted C20 nanocage than unsubstituted C20 nanocage which is necessary to avoid clustering for multiple Ti doped nanocages. Among the eight Ti doped nanocages considered, H2 molecules strongly interact with Ti-doped C12B4N4 nanocage. The binding strength of Ti atom with nanocages decreases during the hydrogen adsorption process. The obtained H2 adsorption energy values for all the structures are within the range of 0.2–0.7 eV, which is conducive to reversible hydrogen storage. Calculated Gibbs free energy-corrected H2 adsorption energy values at different temperature and pressure indicate favorable H2 adsorption over the entire pressure range at room temperature. For Ti doped C20, C12N8, C12B8, C10B5N5, C10B10, B10N10, and B10C10 nanocages, H2 adsorption is thermodynamically favorable below 360, 350, 300, 285, 235, 277, and 251 K, respectively at 1 atm pressure. From PDOS analysis, it is observed that the 1s orbital of H overlaps with 3d orbital of Ti atom. The highest H2 desorption temperature is observed for the C12B4N4Ti nanocage, and the lowest for C10B10Ti, aligning well with the calculated adsorption energy values. As H2 desorption temperature is high, the stability of Ti-doped nanocages at high temperature (634 K) is confirmed using ab initio molecular dynamics simulations. Bader's quantum theory in atoms in molecules is used to prove the weak non-covalent interaction between all the atoms.

Static state synthesis of STT zeolite membranes for high-pressure H2/CH4 separation

STT zeolite membrane with seven-membered rings (7 MR) and nine-membered rings (9 MR) is an ideal alternative for the separation of hydrogen (H2) and methane (CH4). However, the successful synthesis is only possible in rotation conditions, which is difficult to achieve at an industrial scale. Herein we developed a static synthesis approach to prepare high-quality STT zeolite membranes. The precursor transformed in-situ from a liquid state to a semi-solid state to efficiently suppress the nucleation in the bulk gel. This did not affect the growth of the seed layer to form a continuous membrane. The water content was modulated between y = 44 and y = 124 in the molar composition of 1 SiO2: 0.2 TMAdaOH: y H2O. The precursor could be re-used one more time to reduce the total amount of chemical waste. The optimal H2 permeance and H2/CH4 mixture selectivity was up to 6.1 × 10−8 mol m−2 s−1 Pa−1 and 115 at atm pressure. The H2 permeation flux monotonically increased to 2.0 Nm3 m−2 h−1 under feed pressure up to 2.1 MPa. This paves the way for zeolite membranes to high-pressure H2 separation in practical applications.

Reduced kinetics of NH3/n-heptane: Model analysis and a new small mechanism for engine applications

A compact reduced mechanism covering a wide range of conditions is developed for use in simulations of NH3/n-heptane combustion in engines. Reduction targets were selected after reviewing available experimental studies of NH3 combustion in engines. Ignition, flames and oxidation of NH3/n-heptane mixtures were targeted. Particularly, mixtures with very low molar percentage of n-heptane which are important for the applications were considered. They have been observed to have a distinct ignition behavior. Target quantities also included pollutants with a goal to account for two possible mechanisms of N2O formation in engines, discussed in literature. The reduced mechanism of this study was developed with ant colony reduction method. It consists of 57 species and 159 reactions, and its range of applicability is 10–100 atm pressure and 0–100 % NH3 in the fuel mixture. The performance of the mechanism was found comparable to larger models from literature. Importance of carbon–nitrogen interactions, influence of key reactions in the NH3 subset and effect of CO on N2O formation were analyzed and discussed in terms of the predictive ability of the reduced mechanism of the present study and those available from literature.