Porous Carbon Materials Based on Graphdiyne Basis Units by the Incorporation of the Functional Groups and Li Atoms for Superior CO₂ Capture and Sequestration

The graphdiyne family has attracted a high degree of concern because of its intriguing and promising properties. However, graphdiyne materials reported to date represent only a tiny fraction of the possible combinations. In this work, we demonstrate a computational approach to generate a series of conceivable graphdiyne-based frameworks (GDY-Rs and Li@GDY-Rs) by introducing a variety of functional groups (R = −NH₂, −OH, −COOH, and −F) and doping metal (Li) in the molecular building blocks of graphdiyne without restriction of experimental conditions and rapidly screen the best candidates for the application of CO₂ capture and sequestration (CCS). The pore topology and morphology and CO₂ adsorption and separation properties of these frameworks are systematically investigated by combining density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations. On the basis of our computer simulations, combining Li-doping and hydroxyl groups strategies offer an unexpected synergistic effect for efficient CO₂ capture with an extremely CO₂ uptake of 4.83 mmol/g at 298 K and 1 bar. Combined with its superior selectivity (13 at 298 K and 1 bar) for CO₂ over CH₄, Li@GDY-OH is verified to be one of the most promising materials for CO₂ capture and separation

On the Gas-Phase Co⁺-Mediated Oxidation of Ethane by N₂O: A Mechanistic Study

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⁺

Theoretical Investigation of the Reaction of Mn⁺ with Ethylene Oxide

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

Theoretical Investigation of the Methanol Decomposition by Fe⁺ and Fe(C₂H₄)⁺: A π‑Type Ligand Effect

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⁺

Additional file 1: of Insights into the H2/CH4 Separation Through Two-Dimensional Graphene Channels: Influence of Edge Functionalization

Supporting information. Fig. S1. Final configurations of the 1:1 H2/CH4 mixture permeating through the 2D channel of pristine and edge-functionalized GMs (DOCX 4515 kb

Analysis of Petroleum Aromatics by Laser-Induced Acoustic Desorption/Tunable Synchrotron Vacuum Ultraviolet Photoionization Mass Spectrometry

Laser-induced acoustic desorption coupled with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (LIAD/SVUVPI-MS) is employed to analyze aromatics prepared under different conditions from Lungu atmospheric residue (LGAR), i.e., the primary aromatics separated directly from LGAR, and the secondary aromatics after hydrogenation of LGAR and its resins. The mass spectra of the primary aromatics present a bimodal normal distribution in the range of 200–900 Da, in which the relative intensity of the two peaks changes significantly with the SVUV photon energies (9.0, 11.0, and 14.0 eV), indicating that at least two categories of compounds with different ionization energies (IEs) are included, i.e., polycyclic aromatics (IEs < 10.0 eV) in the mass range of 400–900 Da, and aliphatic and alicyclic compounds (IEs close to 11.0 eV) in 200–400 Da. Also detected in the aromatics are metalloporphyrins. Furthermore, the mass spectra of the secondary aromatics separated from LGAR and its resins at different hydrogenation temperatures (390, 400, 410, and 420 °C) are also recorded. The results indicate that the hydrogenation process, especially at higher temperatures, results in removal of alkyl-side and bridge chains in the aromatics, and the secondary aromatics from LGAR resins contain more alkyl side and bridge chains and metal compounds than those from LGAR

Theoretical Survey of the Thiophene Hydrodesulfurization Mechanism on Clean and Single-Sulfur-Atom-Modified MoP(001)

Molybdenum phosphide (MoP) has been extensively experimentally shown to possess high and surprisingly increasing hydrodesulfurization (HDS) activities during the HDS process. In order to understand the HDS mechanism, we investigate the HDS of thiophene on clean and single-sulfur-atom-modified MoP(001) using self-consistent periodic density functional theory (DFT). Thiophene strongly prefers <i>flat</i> adsorption, which is slightly weakened in the presence of a surface S atom. Thermodynamic and kinetic analyses of the elementary steps show that the HDS of thiophene takes place along the direct desulfurization (DDS) pathway on both clean and S-modified MoP(001), because of the very low C–S bond activation barriers as well as very high exothermicities involved. More importantly, the surface S atom does not elevate the C–S bond activation barriers but opens a new concerted pathway for the simultaneous rupture of both C–S bonds in thiophene. These results indicate that the presence of a surface S atom could be helpful for thiophene desulfurization. For comparison, we also investigate the influence of a surface S atom on the HDS of thiophene on Pt(111). The results show clearly a negative effect of the surface S atom, in accordance with the lower sulfur resistance of noble metals

Density Functional Theory Study of the Adsorption and Desulfurization of Thiophene and Its Hydrogenated Derivatives on Pt(111): Implication for the Mechanism of Hydrodesulfurization over Noble Metal Catalysts

Desulfurization of thiophene and its hydrogenated derivatives on Pt(111) are studied using self-consistent periodic density functional theory (DFT), and the hydrodesulfurization network is mapped out. On Pt(111), thiophene has two types of adsorption configurations (parallel cross-bridge and partially tilted bridge-hollow), and for its hydrogenated derivates, the molecule is gradually lifted up from the surface with the addition of hydrogen atoms. In all the adsorbed thiophenic compounds, the S atom is always sp³ hybridized; the C atom in the methylene group is always sp³ hybridized, whereas it is either sp² or sp³ hybridized in the methyne group, depending on how the group interacts with the surface Pt atoms. On the basis of the thermodynamic and kinetic analysis of the elementary steps, a direct desulfurization pathway is proposed for the hydrodesulfurization of thiophene on Pt(111). In contrast to the common thought that hydrogenation toward aromatic organosulfur compounds would make desulfurization easier, the present work clearly demonstrates that hydrogenations of thiophene on Pt(111) do not reduce the energy barrier for the C–S bond cleavage

Initial Hydrogenations of Pyridine on MoP(001): A Density Functional Study

The initial hydrogenations of pyridine on MoP(001) with various hydrogen species are studied using self-consistent periodic density functional theory (DFT). The possible surface hydrogen species are examined by studying interaction of H₂ and H₂S with the surface, and the results suggest that the rational hydrogen source for pyridine hydrogenations should be surface hydrogen atoms, followed by adsorbed H₂S and SH. On MoP(001), pyridine has two types of adsorption modes, i.e., side-on and end-on; and the most stable η⁵(N,C^α,C^β,C^β,C^α) configuration of the side-on mode facilitates the hydrogenation of pyridine. The optimal hydrogenation path of pyridine with surface hydrogen atoms in the Langmuir–Hinshelwood mechanism is the formation of 3-monohydropyridine, followed by producing 3,5-dihydropyridine, in which the two-step hydrogenations take place on the C^β atoms. When adsorbed H₂S is considered as the source of hydrogen, slightly higher hydrogenation barriers are always involved, while the energy barriers for hydrogenations involving adsorbed SH are much lower. However, the hydrogenation of pyridine should be suppressed by the adsorption of H₂S, and the promotion effect of adsorbed SH is limited

The Competitive O–H versus C–H Bond Activation of Ethanol and Methanol by VO₂⁺ in Gas Phase: A DFT Study

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 (Δ<i>E</i>) is found to follow the order of Δ<i>E</i>(C^β–H) < Δ<i>E</i>(C^α–H) ≈ Δ<i>E</i>(O–H). Loss of methyl and glycol occurs respectively via O–H and C^β–H activation, while acetaldehyde elimination proceeds through two comparable O–H and C^α–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 C^α–H activation but also forms VO₂(C₂H₄)⁺ via C^β–H activation. The major product of ethylene is formed via both O–H and C^β–H activation for yielding VO­(OH)₂⁺ and VO₂(H₂O)⁺. In the methanol reaction, both initial O–H and C^α–H activation accounts for formaldehyde and water elimination, but the former pathway is preferred