A novel boron nitrogen monolayer named as inorganic graphenylene (IGP) was proposed for H2 purification, and its stability was confirmed by the calculated cohesive energy and phonon dispersion spectrum. Using the density function theory (DFT) calculations and molecular dynamic (MD) simulations, we found that the IGP membrane can fulfill the requirements of both the high H2 permeance (~10−3 mol/m2 s Pa) and high H2 selectivities (>107) over H2O, CO2, N2, CO, and CH4 at 300 K. Excitingly, the MD results matched well with the DFT calculations including the selectivity, permeance as well as the adsorption properties of different gases.

Monte Carlo simulation calculations were performed to explore the H2S adsorption and separation in the initial MIL-47(V) and the monohalogenated MIL-47(V)-X (X = F, Cl, Br). Both initial and halogenated MIL-47(V) metal–organic framework materials (MOFs) exhibit an ultra-high H2S adsorption ability, which is much higher than that of CH4 and N2. Halogen functionalization could enhance the H2S uptake in unit volume of MOFs especially in low-pressure range, with the sequence: MIL-47(V) < MIL-47(V)-F < MIL-47(V)-Cl < MIL-47(V)-Br, according with the increasing polarizability of the linkers, whereas the H2S mass fraction follows an inverse order MIL-47(V) > MIL-47(V)-F > MIL-47(V)-Cl > MIL-47(V)-Br, because of the increasing mass density of MOFs after halogenation. The adsorption behavior of four MOFs for the H2S/CH4 and H2S/N2 mixtures are explored as a function of both pressure and H2S mole fraction, and all of four MOFs show the ultraselectivity toward H2S molecule. Compared to the initial MIL-47(V), the halogenated MOFs exhibit the preferable H2S/CH4 and H2S/N2 selectivity under the conditions of low temperature, high pressure, and high H2S mole fraction.

The photoionization and fragmentation of octadecane were investigated with infrared laser desorption/tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (IRLD/VUV PIMS) and theoretical calculations. Mass spectra of octadecane were measured at various photon energies. The fragment ions were gradually detected with the increase of photon energy. The main fragment ions were assigned to radical ions (CnH2n+1+, n = 4–11) and alkene ions (CnH2n+, n = 5–10). The ionization energy of the precursor and appearance energy of ionic fragments were obtained by measuring the photoionization efficiency spectrum. Possible formation pathways of the fragment ions were discussed with the help of density functional theory calculations.

Density functional theory has been used to probe the mechanism of gas-phase methanol decomposition by bare Fe+ and ligated Fe(C2H4)+ in both quartet and sextet states. For the Fe+/methanol system, Fe+ could directly attach to the O and methyl-H atoms of methanol, respectively, forming two encounter isomers. The methanol reaction with Fe+ prefers initial C–O bond activation to yield methyl with slight endothermicity, whereas CH4 elimination is hindered by the strong endothermicity and high-energy barrier of hydroxyl-H shift. For the Fe(C2H4)+/methanol system, the major product of H2O is formed through six elementary steps: encounter complexation, C–O bond activation, C–C coupling, β-H shift, hydride H shift, and nonreactive dissociation. Both ligand exchange and initial C–O bond activation mechanisms could account for ethylene elimination with the ion products Fe(CH3OH)+ and (CH3)Fe(OH)+, respectively. With the assistance of a π-type C2H4 ligand, the metal center in the Fe(C2H4)+/CH3OH system avoids formation of unfavorable multi-σ-type bonding and thus greatly enhances the reactivity compared to that of bare Fe+.

A combination of grand canonical Monte Carlo (GCMC) and density functional theory (DFT) simulations was used to investigate the effect of modified metal center in ligand for CO2 capture in novel Zr-based porphyrinic metal–organic frameworks (PCN-224-Ms, M = Mg, Fe, Co, Ni, Mn, and Zr). The results show that the MTCPP ligands (TCPP = tetrakis(4-carboxyphenyl)porphyrin) provide more favorable adsorption sites than the inorganic Zr6 nodes for CO2 molecules. The modification of metal center in MTCPP ligand has a remarkable effect on the single-component adsorption of CO2 compared to CH4 and thus enhances the adsorption of CO2 and the selectivity of CO2 over CH4. Furthermore, Coulomb interaction between adsorbate and framework plays a dominant role compared with non-Coulomb interaction in the process of adsorption and separation. Among various modified metal centers, the Zr-MTCPP is found to be the best for enhancing the adsorption and selectivity of CO2. In addition, a small amount of water has a negative effect on the selectivity of CO2/CH4, and its influence follows the order PCN-224-Zr > PCN-224-Mn > PCN-224-Ni, depending on the strength of Coulomb interaction between H2O molecules and frameworks.

Self-consistent periodic density functional theory (PW91-GGA) calculations are employed to study the oxidation of methanol on PtRu(111). Geometries and energies for all the intermediates involved are analyzed, and the oxidation network is mapped out to illustrate the reaction mechanism. On PtRu(111), the Ru atoms with less electronegativity are more favorable to binding the adsorbates than the Pt atoms. Alloying Pt with Ru weakens the bond of CO to Pt, but strengthens the bond of CO to Ru. All possible pathways through initial C–H, O–H, and C–O bond scissions are considered. The initial O–H bond scission is found to be the most favorable and bears an energy barrier comparable to that for methanol desorption. The further oxidation occurs preferentially via the non-CO path from species CHO. The most possible reaction pathway of methanol on PtRu(111) is CH3OH → CH3O → CH2O → CHO → CHOOH → COOH → CO2. Furthermore, the activation of H2O on PtRu(111) is more favorable than that on the pure Pt(111) surface. The enhancement of methanol oxidation catalytic activity of the PtRu alloy is due primarily to altering the major reaction pathways from the CO path on pure Pt to the non-CO path on the alloy surface as well as promoting adsorption of methanol and formation of active OH species from H2O.

The activation of ethanol and methanol by VO2+ in gas phase has been theoretically investigated by using density functional theory (DFT). For the VO2+/ethanol system, the activation energy (ΔE) is found to follow the order of ΔE(Cβ–H) < ΔE(Cα–H) ≈ ΔE(O–H). Loss of methyl and glycol occurs respectively via O–H and Cβ–H activation, while acetaldehyde elimination proceeds through two comparable O–H and Cα–H activations yielding both VO(H2O)+ and V(OH)2+. Loss of water not only gives rise to VO(CH3CHO)+ via both O–H and Cα–H activation but also forms VO2(C2H4)+ via Cβ–H activation. The major product of ethylene is formed via both O–H and Cβ–H activation for yielding VO(OH)2+ and VO2(H2O)+. In the methanol reaction, both initial O–H and Cα–H activation accounts for formaldehyde and water elimination, but the former pathway is preferred.

The potential energy surfaces of Mn+ reaction with ethylene oxide in both the septet and quintet states are investigated at the B3LYP/DZVP level of theory. The reaction paths leading to the products of MnO+, MnO, MnCH2+, MnCH3, and MnH+ are described in detail. Two types of encounter complexes of Mn+ with ethylene oxide are formed because of attachments of the metal at different sites of ethylene oxide, i.e., the O atom and the CC bond. Mn+ would insert into a C–O bond or the C–C bond of ethylene oxide to form two different intermediates prior to forming various products. MnO+/MnO and MnH+ are formed in the C–O activation mechanism, while both C–O and C–C activations account for the MnCH2+/MnCH3 formation. Products MnO+, MnCH2+, and MnH+ could be formed adiabatically on the quintet surface, while formation of MnO and MnCH3 is endothermic on the PESs with both spins. In agreement with the experimental observations, the excited state a5D is calculated to be more reactive than the ground state a7S. This theoretical work sheds new light on the experimental observations and provides fundamental understanding of the reaction mechanism of ethylene oxide with transition metal cations.

The potential energy surface (PES) corresponding to the Co+-mediated oxidation of ethane by N2O has been investigated by using density functional theory (DFT). After initial N2O reduction by Co+ to CoO+, ethane oxidation by the nascent oxide involves C–H activation followed by two possible pathways, i.e., C–O coupling accounting for ethanol, Co+-mediated β–H shift giving the energetically favorable product of CoC2H4+ + H2O, with minor CoOH2+ + C2H4. CoC2H4+ could react with another N2O to yield (C2H4)Co+O, which could subsequently undergo a cyclization mechanism accounting for acetaldehyde and oxirane and/or a direct H-abstraction mechansim for ethenol. Loss of oxirane and ethenol is hampered by respective endothermicity and high kinetics barrier, whereas acetaldehyde elimination is much energetically favorable. CoOH2+ could facilely react with N2O to form OCoOH2+, rather than Co(OH)2+ or CoO+.

We report herein a comprehensive study of the gas-phase Fe+-mediated oxidation of ethane by N2O on both the sextet and quartet potential energy surfaces (PESs) using density functional theory. The geometries and energies of all the relevant stationary points are located. Initial oxygen-atom transfer from N2O to iron yields FeO+. Then, ethane oxidation by the nascent oxide involves C–H activation forming the key intermediate of (C2H5)Fe+(OH), which can either undergo C–O coupling to Fe+ + ethanol or experience β-H shift giving the energetically favorable product of FeC2H4+ + H2O. Reaction of FeC2H4+ with another N2O constitutes the third step of the oxidation. N2O coordinates to FeC2H4+ and gets activated by the metal ion to yield (C2H4)Fe+O(N2). After releasing N2 through the direct H abstraction and/or cyclization pathways, the system would be oxidized to ethenol, acetaldehyde, and oxirane, regenerating Fe+. Oxidation to acetaldehyde along the cyclization –C–to–C hydrogen shift pathway is the most energetically favored channel.

•Three graphdiyne-like membranes were designed and their stabilities were confirmed.•The DFT and MD results claimed a tunable gas separation property of the membranes.•Graphdiyne modified with F or O can effectively separate CO2/N2/CH4 mixtures.Three graphdiyne-like monolayers were designed by substituting one-third diacetylenic linkages with heteroatoms hydrogen, fluorine, and oxygen (GDY_X, X = H, F, and O), respectively. The CO2/N2/CH4 separation performance of the designed graphdiyne-like monolayers was investigated by using both first-principle density functional theory (DFT) and molecular dynamic (MD) simulations. The stabilities of GDY_X monolayers were confirmed by the calculated cohesive energies and phonon dispersion spectra. Both the DFT and MD calculations demonstrated that although the GDY_H membrane has poor selectivity for CO2/N2/CH4 gases, the GDY_F and GDY_O membranes can excellently separate CO2 and N2 from CH4 in a wide temperature range. Moreover, the CO2/N2 mixture can be effectively separated by GDY_O at temperatures lower than 300 K. Based on the kinetic theory, extremely high permeances were found for CO2 and N2 passing through the GDY_X membranes (10−4–10−2 mol/m2 s Pa at 298 K). In addition, the influence of relative concentration on selectivity was also investigated for gases in the binary mixtures. This work provides an effective way to modify graphdiyne for the separation of large molecular gases, which is quite crucial in the gas separation industry.Graphdiyne monolayer membrane modified by fluorine or oxygen can effectively separate CO2/N2/CH4 mixtures.Figure optionsDownload full-size imageDownload high-quality image (245 K)Download as PowerPoint slide

•Two dumbbell-shaped porous γ-graphyne membranes were designed for H2 purification.•The H2 separation performance of the membranes were studied using both DFT and MD simulations.•Both the graphyne-like membranes can separate H2 with excellent selectivity and acceptable permeance.Two dumbbell-shaped porous γ-graphynes were designed by substituting one-third acetylenic linkages with heteroatoms nitrogen and hydrogen named γ-GYN and γ-GYH, respectively. The calculated cohesive energies and phonon dispersion spectra indicate the possibility to realize the new membranes in experiments. The separation performance of the designed monolayers for H2 from H2O, CO2, N2, CO, and CH4 was investigated using both first-principle density functional theory (DFT) and molecular dynamic (MD) simulations. The DFT calculations suggest the designed membranes are excellent in H2 separation because of the super high selectivities of H2 over other gases H2O, CO2, N2, CO, and CH4 (>1010, 1013, 1021, 1018, and 1046, respectively, at room temperature) together with the high/extremely low permeances for H2/other gases, e.g., reaching the industrial standard at 400 K (γ-GYN) and 425 K (γ-GYH)/lower than the industrial limit by 3–22 orders even at 600 K. The MD simulations indicates that only H2 in the gas mixture containing H2, H2O, CO2, N2, CO, and CH4 can penetrate across the membranes even at the temperature of 600 K and γ-GYN is more favorable for H2 penetration. All these results indicate both the designed membranes, especially γ-GYN, are excellent candidates for H2 purification from gas mixtures.Dumbbell-shaped porous γ-graphynes γ-GYN and γ-GYH can effectively separate H2 from H2O, CO2, N2, CO, and CH4.