Oxidation of methane and ethylene over Al incorporated N-doped graphene: A comparative mechanistic DFT study.

It is generally recognized that developing effective methods for selective oxidation of hydrocarbons to generate more useful chemicals is a major challenge for the chemical industry. In the present study, density functional theory calculations are conducted to examine the catalytic partial oxidation of methane (CH4) and ethylene (C2H4) by nitrous oxide (N2O) over Al-incorporated porphyrin-like N-doped graphene (AlN4-Gr). Adsorption energies for the most stable configurations of CH4, C2H4, and N2O molecules over the AlN4-Gr catalyst are determined to be -0.25, -0.64, and -0.40 eV, respectively. According to our findings, N2O can be efficiently split into N2 and Oads species with a negligible activation energy on the AlN4-Gr surface. Meanwhile, CH4 and C2H4 molecules compete for reaction with the activated oxygen atom (Oads) that stays on the surface. The energy barriers for partial methane oxidation through the CH4 + Oads → CH3° + HOads and CH3° + HOads → CH3OH reaction steps are 0.16 eV and 0.27 eV, respectively. Furthermore, the produced CH3OH may be overoxidized by Oads to give formaldehyde and water molecules by overcoming a relatively low activation barrier. The activation barriers for C2H4 epoxidation are small and comparable to those for CH4 oxidation, implying that AlN4-Gr is highly active for both reactions. The high energy barrier for the 1,2-hydrogen shift in the OCH2CH2 intermediate, on the other hand, makes the production of acetaldehyde impossible under normal conditions. According to the population analysis, the AlN4-Gr serves as a strong electron donor to aid in the charge transfer between the Al atom and the Oads moiety, which is necessary for the activation of CH4 and C2H4. The findings of the present study may pave the way for a better understanding of the catalytic oxidation the CH4 and C2H4, as well as for the development of highly efficient noble-metal free catalysts for these reactions.

Sc-functionalized porphyrin-like porous fullerene for CO2 storage and separation: A first-principles evaluation.

In recent years, there has been a lot of interest in capturing and storing carbon dioxide (CO2) on porous materials as an efficient method for decreasing the adverse effects of this greenhouse gas on the environment and climate change. The current work introduces a Sc-decorated porphyrin-like porous fullerene (Sc6@C24N24) as an efficient material for CO2 capture, storage, and separation using density functional theory calculations. While CO2 is physisorbed over pristine C24N24, the addition of Sc atoms on the N4 sites of C24N24 greatly enhances CO2 adsorption energy. Each Sc atom in Sc6@C24N24 may adsorb up to three CO2 molecules, resulting in a gravimetric density of 48%. Moreover, temperature may be used to modulate CO2 adsorption/desorption over the substrate. The Sc-decorated C24N24 fullerene exhibits a lower affinity for adsorbing N2, CH4, and H2 molecules than CO2. As a consequence, this material might be considered for purifying CO2 molecules from CO2/N2, CO2/CH4, and CO2/H2 mixtures. This study also sheds light on the nature of the Sc-CO2 interaction as well as the underlying mechanism of selective CO2 adsorption on Sc decorated C24N24.

Catalytic CO oxidation reaction over N-substituted graphene nanoribbon with edge defects.

Density functional theory calculations, including dispersion effects, are used to demonstrate how substitutional nitrogen atoms can improve the catalytic reactivity of graphene nanoribbons (GNR) with edge defects in the CO oxidation process. It is demonstrated that the addition of nitrogen impurities significantly enhances O2 adsorption on GNR. Carbon atoms near the edges of defects are the most active sites for capturing O2 molecules. The lower adsorption energy of CO relative to O2 implies that the N-modified GNR is resistant to CO poisoning. The Eley-Rideal (E-R) mechanism has activation energies as low as 0.38 eV, making it the most energetically relevant pathway for the CO + O2 reaction. The findings of this study might help in the design of catalysts for metal-free catalysis of CO oxidation.

Synergic effects between boron and nitrogen atoms in BN-codoped C59-n BN n fullerenes (n = 1-3) for metal-free reduction of greenhouse N2O gas.

The geometries, electronic structures, and catalytic properties of BN-codoped fullerenes C59-n BN n (n = 1-3) are studied using first-principles computations. The results showed that BN-codoping can significantly modify the properties of C60 fullerene by breaking local charge neutrality and creating active sites. The codoping of B and N enhances the formation energy of fullerenes, indicating that the synergistic effects of these atoms helps to stabilize the C59-n BN n structures. The stepwise addition of N atoms around the B atom improves catalytic activities of C59-n BN n in N2O reduction. The reduction of N2O over C58BN and C57BN2 begins with its chemisorption on the B-C bond of the fullerene, followed by the concerted interaction of CO with N2O and the release of N2. The resulting OCO intermediate is subsequently transformed into a CO2 molecule, which is weakly adsorbed on the B atom of the fullerene. On the contrary, nitrogen-rich C56BN3 fullerene is found to decompose N2O into N2 and O* species without the requirement for activation energy. The CO molecule then removes the O* species with a low activation barrier. The activation barrier of the N2O reduction on C56BN3 fullerene is just 0.28 eV, which is lower than that of noble metals.

Strong Tetrel Bonds: Theoretical Aspects and Experimental Evidence.

In recent years, noncovalent interactions involving group-14 elements of the periodic table acting as a Lewis acid center (or tetrel-bonding interactions) have attracted considerable attention due to their potential applications in supramolecular chemistry, material science and so on. The aim of the present study is to characterize the geometry, strength and bonding properties of strong tetrel-bond interactions in some charge-assisted tetrel-bonded complexes. Ab initio calculations are performed, and the results are supported by the quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) approaches. The interaction energies of the anionic tetrel-bonded complexes formed between XF3M molecule (X=F, CN; M=Si, Ge and Sn) and A- anions (A-=F-, Cl-, Br-, CN-, NC- and N3-) vary between -16.35 and -96.30 kcal/mol. The M atom in these complexes is generally characterized by pentavalency, i.e., is hypervalent. Moreover, the QTAIM analysis confirms that the anionic tetrel-bonding interaction in these systems could be classified as a strong interaction with some covalent character. On the other hand, it is found that the tetrel-bond interactions in cationic tetrel-bonded [p-NH3(C6H4)MH3]⁺···Z and [p-NH3(C6F4)MH3]⁺···Z complexes (M=Si, Ge, Sn and Z=NH3, NH2CH3, NH2OH and NH2NH2) are characterized by a strong orbital interaction between the filled lone-pair orbital of the Lewis base and empty BD*M-C orbital of the Lewis base. The substitution of the F atoms in the benzene ring provides a strong orbital interaction, and hence improved tetrel-bond interaction. For all charge-assisted tetrel-bonded complexes, it is seen that the formation of tetrel-bond interaction is accompanied bysignificant electron density redistribution over the interacting subunits. Finally, we provide some experimental evidence for the existence of such charge-assisted tetrel-bond interactions in crystalline phase.

Adsorption of formamide over pristine and Al-doped boron nitride nanosheets: A dispersion-corrected DFT study.

Using the dispersion-corrected DFT calculations, different adsorption modes of formamide molecule are studied over the pristine and Al-doped boron nitride nanosheets (BNNS). It is found that the interaction between the Al atom and its neighboring N atoms in the Al-doped BNNS is very strong, which would hinder the dispersion and clustering of the Al atoms over the BNNS surface. Unlike the pristine nanosheet, the electronic properties of Al-doped BNNS are very sensitive to the formamide adsorption. The adsorption energies of formamide over the Al-doped sheet are in the range of -0.93 to -1.85 eV, which indicates the quite strong interaction of this molecule with the surface. Moreover, the dehydrogenation of formamide over the Al-doped BNNS is examined. According to our results, the N-H bond scission of formamide is more energetically favorable than the C-H one.