Gas Molecules Research Articles

CO in situ directed highly efficient CrOx@silicalite-1 for propane oxidation dehydrogenation by CO2

The propane oxidation dehydrogenation assisted by CO2 (CO2-ODHP) is currently a hot research topic, not only to meet growing demand of propylene but also to favor the CO2 neutralization. In present work, a series of CrOx@S1-n-1.0 with different Cr contents (n= 2.2, 3.6 and 4.5 wt%) is synthesized based on a small gas molecule directing synthesis strategy, wherein the gaseous CO of 1.0 MPa was in situ introduced in the synthesis system to regulate the interaction and dispersion of CrOx over silicalite-1 (S1) support. The characterization results of XRD, XPS, H2-TPR, and Raman indicate that the CO can affect the oxidation state and dispersion of Cr species. As observed, the Cr species were highly dispersed over CrOx@S1–3.6 %-1.0 (in the form of Cr6+ valance state), which however would aggregate to generate Cr2O3 nanoparticles over the CrOx@S1–3.6 %-0a prepared by impregnation method in absence of CO. The activity measurement indicates that the CrOx@S1–3.6 %-1.0 possesses the highest activity by displaying an average propane conversion of 50.4 % and CO2 conversion of 23.6 % at 600 °C, which surpasses most of the literature reports. The CO2-ODHP reaction mechanism was further investigated by in situ DRIFTS, which indicates that dissociated H of propane can react with CO2 to form formate (-COOH), in turn further reacts with H to produce byproducts CO and H2O, and the formate species can also react with the CrO3 active site to form bicarbonate species (HCO-3). Generally, present work has proposed a small gas molecule directing strategy to adjust the dispersions and chemical states of the loaded guest meals over catalytic support. The study of present work would contribute to other highly efficient catalyst design.

Mechanisms of CO2-rich industrial waste gas enhanced shale oil recovery in kerogen slit based on adsorption behavior, gas flooding and surfactant synergy study

Enhanced oil recovery (EOR) by injection of CO2-rich industrial waste gas has been proposed as an energy-efficient and environmentally friendly method for shale oil reservoirs, in which the waste gas can be utilized and sequestered to reduce greenhouse gas emissions. In this work, the adsorption behaviors of shale oil and waste gas components in kerogen slits and the effects of gas flooding on EOR were investigated using molecular dynamics (MD) method, which can provide technical guide for shale oil development. In terms of the adsorption behaviors, an intensity decrease of oil adsorption is observed in kerogen slits after the injection of the waste gas components. Desorption of shale oil during injection of SO2 and CO2 is more pronounced in shallow reservoirs, whereas it is more evident for NO and N2 in deep reservoirs. The desorption efficiency can be 10.91 % for pure CO2 injection and 9.09 % for NO injection at a depth of 1000 m, and the relative stability ratios of CO2 and NO sequestration are 77.09 % and 76.06 %, respectively. For gas flooding, the existence of pressure difference provides favorable conditions for gas molecules to pass through the oil zone, and waste gas can be more effective than pure CO2 as driving gas. For the waste gas injection, the percentage of CO2 retained in the kerogen nanopores is much higher than that of pure CO2 injection, suggesting that more CO2 molecules can enter into kerogen matrix to take part in the displacement process. Furthermore, the effect of surfactants on oil desorption and displacement was also investigated and the interaction energy of the surfactant/oil/gas system was calculated and analyzed, finding that addition of the oil-soluble surfactants can be beneficial to shale oil displacement. This work can provide a comprehensive evaluation of the feasibility of CO2-rich industrial waste gas application for EOR, which is of great significance in the effective production of shale oil and the sequestration of waste gas in shale reservoirs.

Proposal and application of a novel isothermal model for the thermodynamic study of ion exchange reactions

Ion exchange is a separation and purification technique widely employed in chemistry, environment and metallurgy. Commonly, the isotherm models used for thermodynamic study are the Langmuir model and the Freundlich model. However, these two models are initially used to study the adsorption of gas molecules onto solids, and there are some limitations if they are applied to ion exchange reactions. In this paper, a novel isotherm model (NIM) for ion exchange reactions was derived based on the process of ion exchange, the principle of electroneutrality and the law of conservation of mass. The NIM was utilized to study the reactions of anions (F-, WO42-, MoO42-, PO43-, AsO43-, MoS2O22-, MoS42-) with chloride-form strongly basic anion exchange resins. Moreover, the reactions of cations (K+, Ca2+) with sodium-form cation exchange resins were also explored. The results indicated that the calculation data based on the NIM matched up well with the experiments, even though the ions have various valences and different affinities for the resin, which proved the reliability of the model. In addition, the compatibility of the NIM with the Langmuir and Freundlich models was theoretically analyzed, and the conclusions were also verified by the experimental data. By contrast, the physical meaning of the parameters involved in the NIM was clear and had a good generality, which can be applicable to various situations of ion exchange reactions. Therefore, the NIM proposed in this work can effectively obtain the thermodynamic parameters of ion exchange reactions, and is expected to provide theoretical basis for the design, optimization and control of ion exchange processes.

Gas Detecting Evaluation by Graphitic-based Silicon Carbide Nanosurface doped with Manganese: A Promising Device for Air Pollution Monitoring

Silicon carbide (SiC) as a direct broad bandgap semiconducting material has the potential to bring a considerable developement into optoelectronic and electronic devices. This article aims to investigate Physico-chemical properties of manganese (Mn)–doped graphene-like silicon carbide (SiC) monolayer sheet by the first-principles methods based on the density functional theory (DFT) for scavenging of CO, CO2, NO, NO2 gas molecules. The results recommend that the adsorption of these gas molecules on Mn-embedded SiC sheet monolayer is more energetically desired than that on the pristine ones. Gas molecules of CO, CO2, NO, NO2 have been adsorbed on the Mn site of doped SiC monolayer through the formation of covalent bonds. The assumption of chemical adsorptions has been approved by the projected density of states (PDOS) and charge density difference plots. Charge density difference calculations also indicate that the electronic densities were mainly accumulated on the adsorbate of CO, CO2, NO, NO2 gas molecules. The ability of SiC nanosheet for monitoring of CO, CO2, NO and NO2 is fluctuated by their selectivity and sensitivity through NMR, NQR, IR and HOMO/LUMO approaches which can represent the efficiency of Mn–doped SiC surface as the promising sensors toward air pollution detecting.

Effects of leucine on hydrate formation: A combined experimental and molecular dynamics study

Compared to conventional natural gas storage and transportation methods, hydrates offer a safer, more compact alternative with broad future potential. To enhance hydrate formation, there has been considerable interest in environmentally friendly and cost-effective amino acid promoters, such as leucine. This study utilized a transparent vessel for CH4 hydrate formation experiments, identifying the optimal 0.5–0.6 wt% leucine concentration, which led to enhanced gas consumption, shorter induction time, and maximum gas storage density. In the leucine system, hydrates exhibited distinctive branching growth on container walls, both upward and downward. The formation of numerous microchannels amplified capillary effects, enhancing gas–liquid contact and fostering hydrate formation. Simultaneously, isobaric-isothermal molecular dynamics (MD) simulations integrated system growth configurations, structural parameters, radial distribution functions, energy barriers and mean square displacements, unveiling leucine’s microscopic impact on hydrate formation. Simulation results unequivocally show that leucine significantly accelerates CH4 hydrate growth by momentarily adsorbing at the solid–liquid interface, expediting water molecule ordering into cage-like structures. Leucine also enhances water molecule structural order around the mobile leucine molecule. Moreover, leucine lowers the energy barrier for methane transitioning from gas to liquid, facilitating gas molecule diffusion into the liquid phase and affording plenty interaction time for water and methane molecules, thereby providing favorable conditions for hydrate formation. These findings provide crucial perspectives for future research in the field of eco-friendly hydrate promoters, paving the way for innovative solutions in natural gas storage and transportation.

Constructing gradient porosity beyond sieving-kinetics trade-off: Rapidly precise CO2/CH4 separation on carbon nanofibers

Adsorption-based capture of carbon dioxide (CO2) to upgrade natural gas offer a promising solution for energy crisis and the reduction of CO2 emission. However, trade-off between high adsorption selectivity and rapid kinetic is an inherent shortcoming of size-sieving based adsorptive separation of gas molecules at similar sizes, hindering the launch of sieving adsorbent for practical challenging selective gas capture. Herein, a gradiently porous carbon nanofiber PCF-800 with interconnected sieving ultramicropores and low-proportion surficial mesopores is tailor-made to simultaneously realize the exclusive and rapid capture of CO2 from CH4. Arising from the unique interconnected micro-mesoporous structure, the as-prepared PCF-800 not only achieves remarkable uptake ratio of 45 (298 K, 1 bar) for CO2/CH4 separation via size-sieving effect but also shows fast kinetic with diffusion rate of 1.35 × 10-3 s−1, outperforming the conventional ultramicroporous counterpart. Moreover, the impressive dynamic CO2/CH4 separation factor up to 21.7 and satisfying cycling durability revealed by the breakthrough experiments further imply the industrial potential of PCF-800 in practical CH4 purification. This work may shed light on the design of gradient sieving carbonaceous adsorbent with high selectivity and fast kinetic for extensive high-performance small gas separation.

CO oxidation mechanism of silver-substituted Mo/Cu CO-dehydrogenase. Analogies and differences to the native enzyme.

The aerobic oxidation of carbon monoxide to carbon dioxide is catalysed by the Mo/Cu-containing CO-dehydrogenase enzyme in the soil bacterium Oligotropha carboxidovorans, enabling the organism to grow on the small gas molecule as carbon and energy source. It was shown experimentally that silver can be substituted for copper in the active site of Mo/Cu CODH to yield a functional enzyme. In this study, we employed QM/MM calculations to investigate whether the reaction mechanism of the silver-substituted enzyme is similar to that of the native enzyme. Our results suggest that the Ag-substituted enzyme can oxidize CO and release CO2 following the same reaction steps as the native enzyme, with a computed rate-limiting step of 10.4 kcal/mol, consistent with experimental findings. Surprisingly, lower activation energies for C-O bond formation have been found in the presence of silver. Furthermore, comparison of rate constants for reduction of copper- and silver-containing enzymes suggests a discrepancy in the transition state stabilization upon silver substitution. We also evaluated the effects that differences in the water-active site interaction may exert on the overall energy profile of catalysis. Finally, the formation of a thiocarbonate intermediate along the catalytic pathway was found to be energetically unfavorable for the Ag-substituted enzyme.

Microscopic dynamics of gas molecules confined in porous channel-like ice structure

Microscopic dynamics of gas molecules confined in porous channel-like ice structure

A comparative study of NH3 and H2S sensing performance on monolayer nanosheets through first-principle studies

This study investigates the sensing of H2S and NH3 over 2D nanosheets, namely graphene (GRA), boron nitride (BN), silicon carbide (SiC) and boron carbon nitride (BCN), using the first principle density functional theory. A CAM-B3LYP/6–31 G level of theory was used for all the computations and evaluation of the geometric and electronic properties. The optimized clusters indicated the chemisorption between the gas molecules and the SiC nanosheet. The Fourier transform infrared (FTIR) spectra were obtained to study the N-H and S-H shifts in the post-adsorption clusters. Based on the magnitude of the computed adsorption energies, SiC (-0.61 eV for the H2S cluster and −1.21 eV for the NH3 cluster) was found to adsorb both the gas molecules most effectively. The electrostatic potential maps and the molecular orbitals' distribution were studied to investigate the electronic properties. The analysis showed that the adsorption of H2S and NH3 over GRA, BN, and BCN was physical, whereas, on SiC, nanosheet chemisorption was observed. Atom-In-Molecule (AIM) analysis was carried out to account for the possible weak interactions. The study concluded that the SiC nanosheet was the most suitable for the adsorption of H2S and NH3 gases.

Pt, Pd and Au decorated reduced graphene oxide: Sensing properties for phenol gas detection at room temperature

The adsorbent and sensor properties of metal decorated (Pt, Au and Pd) reduced graphene oxide (rGO) structures for phenol gas were investigated using Density Functional Theory (DFT) method with WB97XD formalism. The NBO charge values suggest the occurrence of charge transfer from the phenol molecule to the rGO structures. After the adsorption of phenol, the HOMO-LUMO gap values of the Pt-decorated rGO structure were observed to decrease, while the work function values of the Pt-decorated rGO structure were found to increase. The recovery time for phenol molecule on the Pt-rGO structure was determined to be 0.0019 seconds. These results imply that the Pt-decorated rGO structure can function as a work function sensor in addition to an electronic sensor for phenol gas molecule.

Electrochemical C(sp3)−H Functionalization Using Acetic Acid as a Hydrogen Atom Transfer Reagent

AbstractIn this study, we developed a novel electrochemical protocol that enables the functionalization of inherently inert C(sp3)−H bonds. In this protocol, one‐electron oxidation of acetic acid was used to successfully generate methyl radical, which cleaves the benzylic C(sp3)−H bonds of the substrates via a hydrogen atom transfer (HAT) process, and further reaction with the formed species yields the targeted C(sp3)−H functionalized products. To the best of our knowledge, this is the first example of the use of acetic acid in a HAT process. Notably the reaction has environment‐friendly and fine atom economy nature: the reaction is driven by the electrochemical conditions in the absence of expensive or hazardous reagents, producing only gaseous small molecules, hydrogen, carbon dioxide, and methane, as side products.

Ionization Processes of Negative Corona Discharge Part 1. Review and Experiment

The purpose of the research is an experimental study of physical processes in the near-electrode zones of negative point electrodes in an electronegative gas (air) under the condition of a high-voltage field.Methods. Video image analysis, current-voltage characteristics measurements, and spectroscopy are used. The current-voltage characteristics of the corona discharge ignition voltage in the environment are measured, the problem of experimental identification of surface charges, the mechanism of negative corona discharge ignition, and the ionic structure of streamers is studied, degradation of electrodes during negative corona discharge, spectrum of corona discharge creation and electromagnetic sound.Results. It is shown that at small radii of curvature of needle electrodes, the development of a negative corona discharge is due to the cold emission of electrons, and on flat and slightly curved negative electrodes, due to the capture of surface electrons by electron-withdrawing molecules. The mechanism of ignition of a corona discharge in an electronegative gas with a negative needle, the structure of streamers from negative needles, the emission spectrum and ethonic degradation of electrodes have been studied.Conclusions. The ignition of a negative corona discharge at small radii of the tips of the pointed needles (ro less than tens of microns) is due to the cold emission of electrons followed by impact ionization of neutral molecules. With slightly curved electrodes, the appearance of a negative corona discharge is due to the capture of surface electrons by electronegative gas molecules with subsequent plasma-chemical reactions. The formation of surface electrons depends on many factors: the presence and structure of oxide films (roughness, defects, etc.), which determine the electron work function and form local fields at the tips of microtips. The appearance of a corona discharge leads to degradation of the corona electrodes, expressed in the spraying of the tips of the points and the melting of the needles. In the dark region of the negative corona discharge (U < U*), photons in the in the ultraviolet spectrum (UV spectrum) are emitted, and when U > U*, in addition to UV photons, photons in the visible region of the spectrum are emitted. Glow fluctuations are caused by the chaotic dynamics of the formation of injection centers (melted tubercles - ectons) on the surface of the corona electrode. The ignition of a corona discharge is accompanied by sound emission with a frequency of about 300 Hz.

Toward a Comprehensive Understanding of the Anomalously Small Contact Angle of Surface Nanobubbles.

Experimental studies have demonstrated that the gas phase contact angle (CA) of a surface nanobubble (SNB) is much smaller than that of a macroscopic gas bubble. This reduced CA plays a crucial role in prolonging the lifetime of SNBs by lowering the bubble pressure and preventing gas molecules from dissolving in the surrounding liquids. Despite extensive efforts to explain the anomalously small CA, a consensus about the underlying reasons is yet to be reached. In this study, we conducted experimental investigations to explore the influence of gas molecules adsorbed at the solid-liquid interface on the CA of SNBs created through the solvent exchange (SE) method and temperature difference (TD). Interestingly, no significant change is observed in the CA of SNBs on highly oriented pyrolytic graphite (HOPG) surfaces. Even for nanobubbles on micro/nano pancakes, the CA only exhibited a slight reduction compared to SNBs on bare HOPG surfaces. These findings suggest that gas adsorption at the immersed solid surface may not be the primary factor contributing to the small CA of the SNBs. Furthermore, the CA of SNBs formed on polystyrene (PS) and octadecyltrichlorosilane (OTS) substrates was also investigated, and a considerable increase in CA was observed. In addition, the effects of other factors including impurity, electric double layer (EDL) line tension, and pinning force upon the CA of SNBs were discussed, and a comprehensive model about multiple factors affecting the CA of SNBs was proposed, which is helpful for understanding the abnormally small CA and the stability of SNBs.

Graphene in gas separation membranes—State-of-the-art and potential spoors

Graphene and derivatives have been frequently used to form advanced nanocomposites. A very significant utilization of polymer/graphene nanocomposite was found in the membrane sector. The up-to-date overview essentially highpoints the design, features, and advanced functions of graphene nanocomposite membranes towards gas separations. In this concern, pristine thin layer graphene as well as graphene nanocomposites with poly(dimethyl siloxane), polysulfone, poly(methyl methacrylate), polyimide, and other matrices have been perceived as gas separation membranes. In these membranes, the graphene dispersion and interaction with polymers through applying the appropriate processing techniques have led to optimum porosity, pore sizes, and pore distribution, i.e., suitable for selective separation of gaseous molecules. Consequently, the graphene derived nanocomposites brought about numerous revolutions in high performance gas separation membranes. The structural diversity of polymer/graphene nanocomposites has facilitated the membrane selective separation, permeation, and barrier processes especially in the separation of desired gaseous molecules, ions, and contaminants. Future research on the innovative nanoporous graphene-based membrane can overcome design/performance related challenging factors for technical utilizations.

Ti-substituted organosilica membranes for H2 sieving: Sol-gel and DFT insights

The fabrication of gas-sieving amorphous silica membranes exhibiting superior thermal/hydrothermal/chemical stability by the facile, scalable and controllable synthesis strategies is highly desired to bring the silica membranes a step closer to large scale deployment. Sol-gel modification of bis(triethoxylsilyl)ethane (BTESE) membrane pore network with Ti substitution resulted with a shift in the molecular level cut-off to smaller molecules establishing ideal selectivity improvement from 13 ± 2 to 20 for H2/N2 and 17 ± 4 to 28 for H2/CH4 at 200 °C. BTESE and analogous Ti-substituted BTESE membranes (BTESE-Ti) exhibited H2 permeances of (0.9–1.2)x10−6 mol/(m2sPa) and 5.8 × 10−7 mol/(m2sPa), respectively, reflecting a difference in their thickness. Decrease in the sol concentration by 2-fold led to an increase in the H2 permeance value to 8.9 × 10−7mol/(m2sPa) at 200 °C for BTESE-Ti membranes. We further theoretically designed amorphous BTESE and BTESE-Ti structures, and simulated their interactions with the gas molecules along with the pore diffusion of H2 as a model system to elucidate the membrane performance through the density functional theory (DFT) calculations. Theoretical findings suggest that the only transport mechanism is the direct transport from the gas phase to the pore entrance by excluding the surface diffusion possibility.

Molecular simulations of hydrogen diffusion in underground porous media: Implications for storage under varying pressure, confinement, and surface chemistry conditions

Assessing the feasibility of porous formations for hydrogen geo-storage demands a comprehensive understanding of hydrogen (H2) transport behavior in porous media at subsurface conditions. In this study, we employ molecular dynamics simulations to evaluate the effects of pressure (20–500 atm), pore size (2–20 nm), and surface composition on H2 diffusion and interactions within organic and inorganic slit pores. Our analysis of H2 density profiles and interaction energies reveals a distinct preference for H2 molecules to adsorb more readily onto graphene surfaces than kaolinite surfaces. However, self-diffusion results demonstrate that H2 molecules interact relatively weakly with both substrate types. Further insights are provided by velocity autocorrelation functions, emphasizing the occurrence of wall-mediated collisions as H2 molecules diffuse along the pore surfaces, particularly within kaolinite. This highlights the significance of surface roughness in mitigating H2 loss via diffusion in subsurface nanopores, given the small molecular size of H2 and its limited interactions with both organic and inorganic materials. Furthermore, the results demonstrate that self-diffusion coefficients in both pore types increase with pore size and decrease with pressure. Notably, surface composition plays a critical role in low-pressure environments, with self-diffusion coefficients beginning to converge beyond a pressure of 100 atm. Self-diffusion coefficients also become less sensitive to slit aperture beyond a pressure of 50 atm. In high-pressure environments, hydrogen transport is governed by thermal collisions between gas molecules, leading to negligible property variations between pore types. These findings hold significance in the investigation of efficient H2 storage within porous media and caprock formations.

Gas-Induced Electrical and Magnetic Modulation of Two-Dimensional Conductive Metal-Organic Framework.

Controlled modulation of electronic and magnetic properties in stimuli-responsive materials provides valuable insights for the design of magnetoelectric or multiferroic devices. This paper demonstrates the modulation of electrical and magnetic properties of a semiconductive, paramagnetic metal-organic framework Cu3(C6O6)2 with small gaseous molecules, NH3, H2S, and NO. This study merges chemiresistive and magnetic tests to reveal that the MOF undergoes simultaneous changes in electrical conductance and magnetization that are uniquely modulated by each gas. The features of response, including direction, magnitude, and kinetics, are modulated by the physicochemical properties of the gaseous molecules. This study advances the design of multifunctional materials capable of undergoing simultaneous changes in electrical and magnetic properties in response to chemical stimuli.

Enantioselective Nickel‐Catalyzed Denitrogenative Transannulation En Route to N‐N Atropisomers

Nickel‐catalyzed transannulation reactions triggered by the extrusion of small gaseous molecules have emerged as a powerful strategy for the efficient construction of heterocyclic compounds. However, it’s asymmetric synthesis remains challenging because of the difficulty in controlling stereo‐ and regioselectivity. Herein, we report the first nickel‐catalyzed asymmetric synthesis of N–N atropisomers by the denitrogenative transannulation of benzotriazones with internal alkynes. A broad range of N–N atropisomers was obtained with excellent regio‐ and enantioselectivity under mild conditions. Moreover, density functional theory (DFT) calculations provided insights into the nickel‐catalyzed reaction mechanism and enantioselectivity control.

Enantioselective Nickel-Catalyzed Denitrogenative Transannulation En Route to N-N Atropisomers.

Nickel-catalyzed transannulation reactions triggered by the extrusion of small gaseous molecules have emerged as a powerful strategy for the efficient construction of heterocyclic compounds. However, it's asymmetric synthesis remains challenging because of the difficulty in controlling stereo- and regioselectivity. Herein, we report the first nickel-catalyzed asymmetric synthesis of N-N atropisomers by the denitrogenative transannulation of benzotriazones with internal alkynes. A broad range of N-N atropisomers was obtained with excellent regio- and enantioselectivity under mild conditions. Moreover, density functional theory (DFT) calculations provided insights into the nickel-catalyzed reaction mechanism and enantioselectivity control.

Low experimental thermal conductivity of zirconium metal-organic framework UiO-66

Using laser flash analysis, the low thermal conductivity of the pressed Zirconium metal-organic framework (UiO-66) powder pellet was obtained. As a result, the density ρ, thermal diffusivity α, specific heat capacity cP, and low thermal conductivity κexp of the pressed UiO-66 powder pellet at 300 K are observed to be 1.258 g/cm3, 0.001 59 cm2/s, 0.7765 J/g K, and 0.156 W/m K, respectively. Due to the presence of the 12-coordinated nodes with six transfer pathways, the thermal transport of the UiO-66 particles is preferred through linkers to metal sites. The low thermal conductivity follows the trend of vacuum < argon (Ar) < air < helium (He) since the entrapped gas molecules provide additional heat transfer channels inside the particles and between the particles. The low thermal conductivity along with a weak temperature-dependent thermal conductivity are elucidated in terms of boundary scattering.