Density Functional Calculation of H₂O/CO₂/CH₄ for Oxygen-Containing Functional Groups in Coal Molecules

Abstract

To investigate the adsorption mechanism of H 2 O, CO 2 , and CH 4 molecules on oxygen-containing functional groups (OFGs) in coal molecules, quantum chemical density functional theory (DFT) simulations were performed to study the partial density of states and Mulliken bond layout of H 2 O molecules bonded to different OFGs. The adsorption energy and Mulliken charge distribution of the H 2 O, CO 2 , and CH 4 molecules for each OFG were determined. The results showed that H 2 O molecules form 2, 1, 1, and 1 hydrogen bonds with −COOH, −OH, —C=O, and −O–R groups, respectively. Double hydrogen bonds connected the H 2 O molecules to −COOH with the smallest adsorption distances and highest Mulliken bond layout values, resulting in the strongest bonding between the H 2 O molecules and −COOH. The most stable configuration for the adsorption of these molecules by the −OH group was when the O–H bond in the OFG served as a hydrogen bond donor and the O atom in the H 2 O molecule served as a hydrogen bond acceptor. The order of the bonding strength between the OFGs and H 2 O molecules was Ph–COOH > Ph–OH > Ph—C=O > Ph–O–R. The adsorption energy calculation results showed that H 2 O molecules have a higher adsorption stability than CO 2 and CH 4 molecules. Compared with the −OH, —C=O, and −O–R groups, the −COOH group had a higher adsorption capacity for H 2 O, CO 2 , and CH 4 molecules. The adsorption stability of the CO 2 molecules for each OFG was higher than that of the CH 4 molecules. From the Mulliken charge layout, it was clear that after the adsorption of the H 2 O molecules onto the OFGs, the O atoms in the OFGs tend to gain electrons, while the H atoms involved in bonding with the H 2 O molecules tend to lose electrons. The formation of hydrogen bonds weakens the strength of the bonds in the H 2 O molecule and OFGs, and thus, the bond lengths were elongated.

One‐step purification of ethylene from acetylene and carbon dioxide by ultramicroporous carbons

“…The C 2 H 2 uptake displayed a good linear relationship with BET surface area and ultramicropore (<0.7 nm) volume (Figure S23). Meanwhile, the oxygen‐containing functional groups can improve the C 2 H 2 adsorption because the enhanced pore surface's polarity could reinforce the interactions between adsorbent and C 2 H 2 molecules with larger quadrupole moments 54,55 . Especially, the C 2 H 2 adsorption capacity positively correlated with the HOCO functionalities (Figure S24).…”

“…Meanwhile, the oxygen-containing functional groups can improve the C 2 H 2 adsorption because the enhanced pore surface's polarity could reinforce the interactions between adsorbent and C 2 H 2 molecules with larger quadrupole moments. 54,55 Especially, the C 2 H 2 adsorption capacity positively correlated with the HO C O functionalities (Figure S24). Moreover, the high-resolution N 1s XPS spectrum showed that N-5 species were the major nitrogen functional groups in CSH-2-700 (Table S2 5A).…”

Density Functional Simulation Study of Surface Wettability of Coal Molecules with Different Degrees of Defects

“…In contrast, only small wave peaks occur on the surfaces of the perfect coal molecules, with a peak of 3.38 electrons/eV. The higher density of states near the Fermi energy level of the defective coal molecule indicates that the electrons on the surface of defective coal molecules are more active. − The projection of the electrostatic potential shows that the smallest electrostatic potential value of the single-vacancy-defective coal molecule surface was located at the defects with a value of −0.041 au (Figure (a)); the smallest electrostatic potential value of the double-vacancy-defective coal molecule surface was around the five-ring aromatic cluster with a value of −0.027 au (Figure (b)); the smallest electrostatic potential value of the perfect coal molecule surface was around the whole 2 × 2 aromatic cluster with a value of −0.025 au (Figure (c)). A comparison of the magnitude of the electrostatic potential values on the surfaces of the different coal molecules reveals that the surfaces of the single-vacancy-defective coal molecules have the highest electron density.…”

A first-principles study of electro-catalytic reduction of CO2 on transition metal-doped stanene

“…The H-bond lengths for Ti@Sn and Fe@Sn are 1.89 and 1.95 Å, respectively, similar to the H-bond lengths reported previously for various oxygen containing functional groups. 75 In addition, the distances between the donor and acceptor atoms in Ti@Sn and Fe@Sn are much shorter than the sum of van der Waals radii of the donor and acceptor atoms and the O-H bond length in H 2 O (ESI †). Furthermore, our Bader charge analysis indicates the shift in electron density: charge on the O atom of water increases while on the C atom of the CO 2 molecule decreases (Table S3, ESI †).…”