CH4 Molecules Research Articles

Direct Ethylene Purification from a Four-Component Gas Mixture by a Microporous MOF with Aromatic Pore Surface and Carboxylates.

The single-step purification of ethylene (C2H4) from a mixture of carbon dioxide (CO2), acetylene (C2H2), ethylene (C2H4), and ethane (C2H6) was achieved through MOF Compound-1, where the aromatic pore surface and carboxylates selectively recognized C2H6 and CO2, respectively, resulting in a reversal of the adsorption orders for both gases (C2H6 > C2H4 and CO2 > C2H4). Breakthrough testing verified that the C2H4 purification ability could be enhanced 2.6 times after adding impure CO2. Grand Canonical Monte Carlo (GCMC) simulations demonstrate that there are interactions between CO2 and C2H6 molecules as well as between CO2 molecules themselves. These interactions contribute to the enhancement of the C2H4 purification ability upon the addition of CO2 and the increased adsorption of CO2.

Unveiling unconventional CH4–Xe compounds and their thermodynamic properties at extreme conditions

Inert gases (e.g., He and Xe) can exhibit chemical activity at high pressure, reacting with other substances to form compounds of unexpected chemical stoichiometry. This work combines first-principles calculations and crystal structure predictions to propose four unexpected stable compounds of CH4Xe3, (CH4)2Xe, (CH4)3Xe, and (CH4)3Xe2 at pressure ranges from 2 to 100 GPa. All structures are composed of isolated Xe atoms and CH4 molecules except for (CH4)3Xe2, which comprises a polymerization product, C3H8, and hydrogen molecules. Ab initio molecular dynamics simulations indicate that pressure plays a very important role in the different temperature driving state transitions of CH4–Xe compounds. At lower pressures, the compounds follow the state transition of solid–plastic–fluid phases with increasing temperature, while at higher pressures, the stronger Xe–C interaction induces the emergence of a superionic state for CH4Xe3 and (CH4)3Xe2 as temperature increases. These results not only expand the family of CH4–Xe compounds, they also contribute to models of the structures and evolution of planetary interiors.

Chemical simulations of quantum systems using quantum computers - review of algorithms and their experimental verification

Computer simulations using ever-increasing computing power and machine learning techniques allow advanced molecular modelling, molecular dynamics simulations and studies of intermolecular interactions. However, due to the complexity of biological systems and chemical processes at the molecular level, their accurate representation using classical computer models and techniques has faced a number of significant limitations for many years. A new and promising direction for the development of computational science and its potential applications in biochemistry is quantum computing and its integration with classical high-performance supercomputing systems. This article responds to the growing interest in the use of available quantum computers in exemplary applications. In this paper, we aim to provide an overview of the basic notions involved in the development of quantum algorithms and simulations related to issues at the interface of quantum chemistry and biochemistry. In addition, the article introduces the basic principles of performing simulations using the state-of-the-art quantum computers in the era of Noisy Intermediate-Scale Quantum (NISQ). Experimental results of the classical-quantum algorithm Variational Quantum Eigensolver (VQE) for example molecules H2 and CH+ are also presented. Despite the many shortcomings of currently available quantum computers, the analysed VQE algorithm proved to be effective in approximating the ground state of molecules using a minimal functional basis.

The dual action of N2 on morphology regulation and mass-transfer acceleration of CO2 hydrate film

The morphology characteristics of CH4, CO2 and CO2+N2 hydrate film forming on the suspending gas bubbles are studied using microscopic visual method at supercooling conditions from 1.0 to 3.0 K. The hydrate film vertical growth rate and thickness along the planar gas-water interface are measured to study the hydrate formation kinetics and mass transfer process. Adding N2 in the gas mixture plays the same role as lowering the supercooling conditions, both retarding the crystal nucleation and growth rates, which results in larger single crystal size and rough hydrate morphology. N2 in the gas mixture helps to delay the secondary nucleation on the hydrate film, which is beneficial to maintain the pore-throat structure and enhance the mass transfer. The vertical growth rate of hydrate film mainly depends on the supercooling conditions and gas compositions but has weak dependence with the experimental temperature and pressure. Under the same gas composition condition, the final film thickness shows a linear relationship with the supercooling conditions. The mass transfer coefficient of CH4 molecules in hydrates ranges from 4.54 to 7.54×10–8 mol·cm–2·s–1·MPa–1. The maximum mass transfer coefficient for CO2+N2 hydrate occurs at the composition of 60% CO2+40% N2, which is 3.98×10–8 mol·cm–2·s–1·MPa–1.

Photoluminescence of L-Valine Irradiated with Small Doses

The measurement technique and the results obtained by optical spectroscopy during excitation of L-valine molecules by photons described. The photoluminescence spectra of L-valine studied in the wavelength range 400-700 nm during excitation by photons of different energies 3.26-4.51 eV. Peculiarities were found in the luminescence spectra (radiation intensity, positions of maxima), indicating the excitation of the OH, CO and CH molecules as fragments of the valine molecule by photon impact. The same results obtained for the samples of L-valine irradiated by electrons with the dozes 0.2, 0.5, 2 and 5 Gy. Irradiation of L-valine leads to fragmentation of carboxyl COOH group. The biggest changes in photoluminescence spectra observed for the sample with 0.2 Gy irradiation doze. Also X-ray powder diffraction spectra measured, which showed absence of any structural changes for the irradiated samples. The results (photoluminescence and XRay structural spectra) of melted at 330o C L-valine sample are presented.

Effect analysis on the hydrocarbon adsorption performance enhancement of the different zeolite molecular sieves in the gasoline engine under the cold start process

In this work, the adsorption performance of ZSM-5, Beta-A, and NON zeolites on hydrocarbons emitted from the engine is investigated for selecting the best suited zeolite molecular sieves for hydrocarbon traps during the cold-start phase of the engine. Based on the giant canonical Monte Carlo (MC) method for adsorption simulation, the single-component, multi-component maximum adsorption, adsorption isotherms, adsorption sites of different hydrocarbon molecules on ZSM-5, Beta-A, and NON molecular sieves were investigated by using C2H2, C2H4, C3H6, and C7H8 molecules as probe molecules. The single-component adsorption results showed that for the macromolecular hydrocarbon toluene (C7H8) Beta-A zeolite had the best adsorption effect, followed by ZSM-5 zeolite, and NON had the worst adsorption effect. The adsorption of propylene (C3H6) on ZSM-5 and Beta-A is close to each other, and the adsorption of ethylene (C2H4) and acetylene (C2H2) are much different relative to C3H6 and C7H8. This is due to the fact that the adsorption properties of zeolites are determined by the molecular diameter of the hydrocarbons. The results of multicomponent adsorption showed that the adsorption amounts of multicomponent competitive adsorption were reduced relative to single-component adsorption, but were affected by other components in different ways, from small to large C7H8<C3H6<C2H4<C2H2.

Reverse Separation of Carbon Dioxide and Acetylene in Two Isostructural Copper Pyridine‐Carboxylate Frameworks

AbstractSeparating acetylene from carbon dioxide is important but highly challenging due to their similar molecular shapes and physical properties. Adsorptive separation of carbon dioxide from acetylene can directly produce pure acetylene but is hardly realized because of relatively polarizable acetylene binds more strongly. Here, we reverse the CO2 and C2H2 separation by adjusting the pore structures in two isoreticular ultramicroporous metal–organic frameworks (MOFs). Under ambient conditions, copper isonicotinate (Cu(ina)2), with relatively large pore channels shows C2H2‐selective adsorption with a C2H2/CO2 selectivity of 3.4, whereas its smaller‐pore analogue, copper quinoline‐5‐carboxylate (Cu(Qc)2) shows an inverse CO2/C2H2 selectivity of 5.6. Cu(Qc)2 shows compact pore space that well matches the optimal orientation of CO2 but is not compatible for C2H2. Neutron powder diffraction experiments confirmed that CO2 molecules adopt preferential orientation along the pore channels during adsorption binding, whereas C2H2 molecules bind in an opposite fashion with distorted configurations due to their opposite quadrupole moments. Dynamic breakthrough experiments have validated the separation performance of Cu(Qc)2 for CO2/C2H2 separation.

Molecular insight on CO2/C3H8 mixed hydrate formation from the brine for sustainable hydrate-based desalination

Systematic molecular dynamics simulations have been performed to investigate the formation of CO2/C3H8 mixed hydrate in brine, to search for the optimal C3H8 content and elucidate the microscopic mechanism for hydrate-based desalination process. Simulation results indicate that the desalination process is significantly affected by the formation kinetics of CO2/C3H8 mixed hydrates due to the diverse physical properties of CO2 and C3H8 molecules in the brine. Specifically, CO2 molecules are more likely to leave the mixed gas nanobubbles and form hydrates, whereas most of C3H8 molecules remain in gas nanobubbles for a prolonged period. Interestingly, ions can form abnormal CO2-occupied and C3H8-occupied hydrate cages by replacing the water molecule in cages, and some ions can also be adsorbed on the surfaces of the cage-like hydrogen bond network or encapsulated between the hydrate solids. The presence of these ions presents a challenge to separating them due to the strong attraction from the water in hydrate solids. On the other hand, it is confirmed that the C3H8 content with 10 % is optimal for CO2/C3H8 mixed hydrate-based desalination, as it promotes the decomposition of mixed gas nanobubbles to form hydrates by suppressing the structural fluctuations in the system. These molecular insights into the effect of C3H8 content on CO2/C3H8 mixed hydrate formation in brine may help to develop hydrate-based desalination technology.

Identifying the key structural features of Ni-based catalysts for the CO2 methanation reaction

Identifying the parameters influencing the selectivity of products is prominently significant for fabricating efficient catalysts. However, little progress has been made in describing the regulation rule of CH4 selectivity toward the CO2 methanation reaction, which is considered a vital process for CO2 emission and conversion. Herein, we disclosed the integral role of the electronegativity of M atoms in Ni-MOx supported catalysts to producing CH4 molecules, which the satisfactory catalytic performance stemmed from the regulated ability to capture CO2 molecules and CO intermediates. More importantly, alongside the extensively studied descriptor of particle size, we uncovered a strong correlation between the electronegativity of M atom and CH4 selectivity, in which the CO/CO2 adsorption capacity upon the Ni/NiOx/MOx interfaces exhibited a volcanic trend based on the electronegativity of M atoms in MOx supports. The screened Ni-Y2O3 composite catalysts demonstrated excellent CO2 methanation performance, suggesting the powerful practicability of the electronegativity of M atoms in MOx supports as a descriptor. These findings not only shed fundamental insight into the reaction pathway but also paved the way for the rational design of Ni-based catalysts based on the simple descriptor of electronegativity.

Hydroxyl-functionalized linker endows an ultra-microporous aluminum based metal–organic framework with electronegative site for enhancing ethane/ethylene separation

Efficient purification of ethylene (C2H4) from the cracking gas containing a small amount of ethane (C2H6) by selective adsorption of C2H6 is meaningful but remains challenging. Aluminum-based metal–organic frameworks (Al-MOFs) with ultra-microporous structure show preferential adsorption of C2H6 over C2H4, relying on the existence of multiple hydrogen bonding acceptors (e.g., AlO6 polyhedra) for C2H6 molecule in the confined pores. However, most Al-MOFs exhibit limited C2H6/C2H4 selectivity (<2), which lack other strong preferential binding sites for C2H6. Here we report that a hydroxyl functionalized Al-MOF (i.e., CAU-1-OH) exhibits notably improved C2H6/C2H4 selectivity (2.13) and C2H6 uptake (3.95 mmol g−1) at 298 K and 1 bar compared to its amino-functionalized counterpart, CAU-1-NH2. Prior to experiment, theoretical calculations were performed, revealing that O atom from hydroxyl group in CAU-1-OH acts as a fairly strong hydrogen bond acceptor due to its more negative charge than N atom in CAU-1-NH2. The in-situ infrared experiment further confirmed the formation of multiple hydrogen bonds (C–H⋅⋅⋅O) between CAU-1-OH and C2H6 molecules, which plays vital role for C2H6-selective capture. The actual potential for C2H4 purification was fully demonstrated by dynamic breakthrough experiments, in which CAU-1-OH displayed excellent separative performance from C2H6/C2H4 (1/15, v/v) mixture. Moreover, the structural stability and excellent recyclability suggested and the promise for cost-effective industrial application in C2H6/C2H4 separation.

First-principle investigation the initial oxidation of methane on Pd doped LaCo0.2Fe0.8O3-δ anode surfaces of solid oxide fuel cells

Initial oxidation of methane (CH4) is essential for subsequent oxidation reactions on anode surfaces of solid oxide fuel cells (SOFCs). Here first principle method was employed to investigate the initial oxidation mechanism of CH4 on Pd doped LaCo0.2Fe0.8O3-δ (LCF) anode. Results show that Pd-doping decreases formation energies of surface oxygen vacancy. The adsorption ability of CH4 molecules is also improved on perfect LCF surface by Pd-doping. Dissociation barriers of CH4 on LCF surfaces are greatly decreased with min value of 1.14 eV by Pd-doping and surface oxygen vacancy compared to those on perfect and defective LCF surfaces (min values of 1.76 and 1.34 eV, respectively). Results of Bader charges and bond lengths of CH4 (or CH3) and OH show that the initial oxidation of CH4 molecules is namely the oxidation of dissociated H atoms from CH4 molecules. And higher valences of surface metal atoms interacted with CH4 molecules mean the lower dissociation barriers of CH4 molecules.

Effect of non metallic doping in GeC gas sensors on gas response performance: the first principles study

In this paper, the stability, electronic structure and optical properties of monolayer GeC, B, N and P doped GeC systems are systematically investigated based on the first principles of density functional theory. The results show that the results show that the intrinsic GeC monolayer has a weak adsorption capacity for CH4 and C2H2, which is unfavourable for the sensing and trapping of CH4 and C2H2 gases. Based on calculated adsorption distance, adsorption energy and charge transfer, we find that P-GeC monolayer is the most sensitive to CH4 and C2H2 molecules, and the most of gas molecules act as acceptors to gain electrons from GeC monolayer. The adsorption energy of CH4 is smaller than that of C2H2 gas molecule, which implies that C2H2 is more easily desorbed from P-GeC. Moreover, the work function changes significantly when gas molecules adsorbed on B, N, P-GeC, and Recovery times indicate that B, N and P doped GeC monolayers are more selective and sensitive to C2H2 molecules compared to CH4 molecules. The research work aims to provide a theoretical basis for the application of GeC-based gas sensors, and P-doped GeC monolayers can be used as candidate materials for C2H2 gas sensing and trapping.

Auxiliary ligand influence on interpenetration and C2H2/CO2 separation in NDI based isoreticular MOFs

Selective separation of C2H2 from CO2 mixtures promises a critical industrial process to produce high-purity C2H2 but challenging due to their similar physical properties and molecular sizes/shapes. Naphthalenediimide (NDI) ligand-based metal − organic frameworks (MOFs) exhibit potential in selective adsorption of C2H2 due to NDI’s high affinity to C2H2 molecules. Here, three iso-reticular NDI based MOFs (denoted as FJU-109, 110 and 111) are obtained by tuning interpenetration using auxiliary ligands of different lengths. Based on the actual column breakthrough experiments, FJU-111 can achieve separation C2H2/CO2 mixture, with a separation selective of 2.2. Calculation of the binding energy shows that C-H…O interactions between guest and O atom from NDI ligand play a dominant role in elective recognition of acetylene.

Physical breakdown of CH4 hydrate under stress: a molecular dynamics simulation study

As a solid energy source, CH4 hydrate will inevitably break down physically as the result of geological movement or exploitation. Here, the molecular dynamics method was employed to simulate the uniaxial-deformation behavior of structure I (sI type) CH4 hydrate under stress. The stress increases regardless of whether the hydrate is stretched or squeezed, and other physical parameters also changed, such as hydrate cage numbers, order parameters, and the number of water molecules. A noticeable difference is observed between the two systems. Upon stretching, the stress immediately recovers to 0 GPa once the hydrate is completely stretched apart. During the squeeze process, the stress is ultimately not zero since solid and liquid are always in contact. When the hydrate is stretched apart, about 5% of water molecules change from solid to liquid, about 7.8% of CH4 molecules lose their shelter and become free due to the disintegration of water cages. While in the squeezing process, large cages (51262) are crushed more easily than small cages (512); in the end, about 93.5% of large cages and 73% of small cages are crushed, and approximately 87.5% CH4 is released from the cages. In mining CH4 hydrates, caution must be exercised, as if the hydrates break as a result of stress, a large release of CH4 may pose a security risk.

First-Principles Predictions of MoS2-WS2 In-Plane Heterostructures for Sensing Dissolved Gas Species in Oil-Immersed Transformers.

This work from first-principles insight uses a MoS2-WS2 in-plane heterostructure as a potential sensing material for detection of CO and C2H2, two typical dissolved gases in oil-immersed transformers, in order to evaluate the operation status. The adsorption performance of the MoS2-WS2 heterostructure upon two gas species is assessed via three adsorption sites and compared with isolated MoS2 and WS2. Results indicate that MoS2-WS2 performs with a much stronger binding force and charge-transfer for adsorptions of CO and C2H2 in comparison to the isolated counterpart, which gives rise to more obvious deformation in the electronic property of MoS2-WS2 as well as a much larger resistance-based sensing response. The recovery time of MoS2-WS2 for desorption of CO and C2H2 molecules is also appropriate to allow the reusability of such a sensor. The findings in this work uncover the admirable sensing potential of transition metal dichalcogenides (TMDs)-based heterostructures upon oil dissolved gases, which opens up a new way to explore novel 2D nanomaterials as resistive gas sensors for dissolved gas analysis in electrical oil-immersed transformers.

Photocatalytic Conversion of Methane to Ethanol at a Three-Phase Interface with Concentration-Matched Hydroxyl and Methyl Radicals.

The direct oxidation of CH4 to C2H5OH is attractive but challenging owing to the intricate processes involving carbon-chain growth and hydroxylation simultaneously. The inherent difficulty arises from the strong tendency of CH4 to overoxidize in the commonly used pressurized powder suspension systems rich in reactive oxygen radicals (ROR), which are specifically designed for CH4 concentration and activation. Meanwhile, the strong tendency of nucleophilic attack of potent ROR on the C-C bond of the resulting product C2H5OH ultimately leads to a higher selectivity for C1 oxygenates. This study addresses this multifaceted issue by designing a three-phase interface based on a hydrophilic floating Fe(III)-cross-linked macroporous alginate hydrogel film encapsulated with C3N4 [Fe(III)@ACN] to simultaneously enhance the accessibility of H2O and CH4 molecules to the active sites and species within the macroporous channel. The hydrophilic properties of Fe(III)@ACN allow the in situ production of H2O2 from C3N4 through the water oxidation reaction under irradiation. The concurrent photoinduced Fe(II) triggers Fenton reaction with H2O2 to produce •OH. The enhanced mass transfer of CH4 at the three-phase interface ensures the efficient formation of •CH3 by reacting with •OH, ultimately facilitating carbon-chain growth in the conversion pathway from CH4 to CH3OH and finally to C2H5OH with •CH3 and •OH present in comparable concentrations. Thus, the Fe(III)@ACN catalyst exhibits a remarkable 96% selectivity for alcohol, achieving a 90% selectivity for C2H5OH in the alcohol products. The C2H5OH production rate reaches 171.7 μmol g-1 h-1 without the need for precious-metal additive.

Molecular dynamics simulations of interfacial resistance of gases transport through MOF HKUST-1

The mass transfer resistances of CH4 and CO2 transport through MOF HKUST-1 were intensively studied by molecular simulations. The corrected diffusivities increase as thickness increases in finite HKUST-1, and converge to the maximum in infinite crystalline. The interfacial resistance plays an essential role in total one, and weakens as HKUST-1 thickness increases. Under the same conditions, CO2 molecules suffer from stronger transport resistance than CH4 counterparts due to enhanced energy barriers, larger molecular weight, stronger interactions and freedom degree loss. The transport resistances decrease with loadings, opposite to trend of gas–gas interactions. The collisions of CH4 and CO2 molecules at high loadings are inclined to specular reflection, and enhance molecular collision, resulting in stronger permeability. Compared to CH4, CO2 exhibits 40% higher interface resistance under identical loading conditions. Such similar quantitative relationship also appears on critical membrane thickness, both of which are on the order of several tens of nanometers.

Efficient mesoporous cross-linkable hybrid poly Schiff-base based on polyimide as a promising molecular sieve for sustainable CO2 capturing and separation

ABSTRACT A cross-linked hybrid poly Schiff-base (PSB) was synthesized and characterized through spectroscopic, morphological, and structural approaches. The BET surface area (SBET) of the PSB is 20.33 m2/g, the pore volume (Vp) is 0.024 cm3/g, and the pore diameter (Dp) is 4.13 nm. The current study elucidates PSB’s strong chemical and thermal stability, as well as the remarkable capacity to adsorb CO2 with perfect selectivity. This property is accomplished by the synergistic interaction of the polymer’s physicochemical and structural features when exposed to CO2, N2 and CH4 molecules. This mesoporous polymer exhibits a CO2/N2 = 60 and CO2/CH4 = 10.5 selectivity, and can adsorb 3.22 mmol/g CO2 (at 298 K/1 bar). Furthermore, the isotherms of CO2 gas adsorption and desorption in the porous polymer are reversible. The use of PSB having effective imide, imine, and meta-hydroxyl functional groups in the adsorption and selectivity of CO2 gas produced excellent results, which make it a suitable candidate for CO2 storage and separation applications.

Plasma-induced methane catalytic cracking: Effects of experimental conditions

Low-carbon conversion of hydrocarbon fuels and feedstocks, as well as the macroscopic production of H2, are central focus in the advancement of high-value and efficient conversion of CH4. The effects of Ar addition ratio, discharge power and temperature on the results of plasma methane cracking were investigated on a dielectric barrier discharge (DBD) plasma experimental system. The results show that the addition of Ar can improve the methane conversion, and the optimal ratio of CH4 conversion to H2 production after the effect is CH4: Ar = 1:1, at which the methane conversion reaches 49.62% and the H2 selectivity reaches 52.66%. The plasma at 25 °C can make the methane conversion close to the effect of catalytic cracking at 600 °C, while the H2 selectivity is lower, the H2 generation is 32.59% lower than the latter, and the products have more C2–C4 hydrocarbon impurities. The solid byproduct resulting from the DBD plasma cracking of methane primarily consisted of carbon black, possessing an average particle size of 62.21 nm. The incorporation of Ar and the amplification of power augment the CH* radical intensities, which suggests both conditions contribute positively to the dissociation of the CH4 molecule.

Wall-trapped acetylene tetramer in a metal-organic framework enables kinetic separation of C2H2/C2H4

Effective separation of acetylene/ethylene (C2H2/C2H4) mixtures by adsorption is a challenging but green method given their similar molecular characters. An increasing number of metal-organic frameworks (MOFs) have addressed the diffusion-related challenges to achieve the separation, yet almost all of them just focus on diffusion rates and disregard the geometrical arrangement of adsorbed molecules which exerts important effects in boosting the diffusion behaviors. Herein, we now present a paradigm using an ultramicroporous zinc-MOF (Zn-MOF, referred to as 1) with assessable size of 3.4 × 3.3 Å2, as demonstrated by single-crystal and theoretical analysis, which realizes the effective separation of C2H2 from its competitors. Static adsorption isotherms indicate that 1 possesses higher C2H2 uptake of 28.4 cm3 g−1 at 298 K and 0.1 bar, achieving a high IAST selectivity of 265 among the benchmark MOFs. Theoretical calculations reveal that C2H2 molecules are grasped through multiple binding interactions and adsorbed in the pore surface rather than the center of the pore, thus forming C2H2 tetramer through connecting four C2H2 motifs. Further, time-dependent kinetic tests coupled with molecular dynamics confirm the faster diffusion behavior for C2H2, mainly attributing to unimpeded diffusion channel. Column breakthrough tests demonstrate that 1 can easily accomplish exclusive separation of C2H2 from various binary ethane dehydrogenation (EDH) and senary non-oxidative coupling of methane (non-OCM) byproducts. Specially, structurally stable 1 can be readily synthesized utilizing inexpensive raw materials, yielding the cost of only $614 per kilogram. Accordingly, this work proposes a novel strategy of wall-trapped C2H2 tetramer in MOF that can effectively promote the kinetic behavior through available diffusion channel, expecting to offer a new perspective and provide guidance for future research.