The mechanisms of ethene methylation with methanol and dimethyl ether have been investigated using a 128T cluster of ZSM-5 zeolite modeled by ONIOM(B3LYP/6-31G(d,p):UFF) and ONIOM(M06-2X/6-311+G(2df,2p):UFF) calculations. The effects of the infinite zeolitic framework on the model of the zeolite nanopocket, which consisted of a quantum cluster of 34 tetrahedral units and of 128 tetrahedral units modeled on the UFF level, were also included. The zeolitic Madelung potential was reproduced by a set of point charges generated by the SCREEP method. The energies for the adsorption of methanol and dimethyl ether on H-ZSM-5 from an ONIOM2(M06-2X/6-311+G(2df,2p):UFF)+SCREEP calculation are -26.3 and -29.4 kcal/mol, respectively, which are in good agreement with the experimental data. Dissociative and associative mechanisms of the ethene methylation by methanol and dimethyl ether have been considered. For the dissociative mechanism, the methylation reaction of ethene starts with the protonation of methanol or dimethyl ether by the acidic zeolite proton to form a surface methoxide intermediate, which subsequently reacts with an ethene molecule forming a propoxide intermediate. The propoxide intermediate is then deprotonated to form the propene product. The activation energies for the first step are computed to be 41.2 and 42.9 kcal/ mol for methanol and dimethyl ether, respectively. The activation energies for the subsequent second and third reaction steps are 21.4 and 26.5 kcal/mol, respectively. For the associative mechanism, protonation and methylation take place simultaneously without formation of a surface methoxide. The calculated activation barriers are 29.0 and 33.0 kcal/mol for methanol and dimethyl ether, respectively, suggesting that methanol should be slightly more reactive than dimethyl ether for the methylation of ethene. The final step in the associative mechanism, the deprotonation of the propoxide intermediate to give the adsorbed propene product, has an activation energy of 25.4 kcal/mol. The results indicate that the associative pathway is favored over the dissociative one and that the rate-determining step of this reaction is the ethene methylation step.

Conversion of greenhouse gases to more valuable chemicals is important from both the environmental and industrial points of view. Herein, the reaction mechanisms of the hydrogenation of carbon dioxide (CO2) to formic acid (HCOOH) over Cu-alkoxide-functionalized metal organic framework (MOF) have been investigated by means of calculations with the M06-L density functional. The reaction can proceed via two different pathways, namely, concerted and stepwise mechanisms. In the concerted mechanism, the hydrogenation of CO2 to formic acid occurs in a single step. It requires a high activation energy of 67.2 kcal/mol. For the stepwise mechanism, the reaction begins with the hydrogen atom abstraction by CO2 to form a formate intermediate. The intermediate then takes another hydrogen atom to form formic acid. The activation energies are calculated to be 24.2 and 18.3 kcal/mol for the first and second steps, respectively. Because of the smaller activation barriers associated with this pathway, it therefore seems to be more favored than the concerted one. The catalytic effect of Cu-MOF-5 is also highlighted by comparing it with the gas-phase uncatalyzed reaction in which the reaction takes place in one step with a barrier of 73.0 kcal/mol. This study also demonstrates that the metal-functionalized MOF can be utilized for the greenhouse gas catalysis in addition to using it to capture and activate CO2.

The effects of the zeolite framework on the mechanism of n-hexane monomolecular cracking have been investigated with M06-2X/6-311+G(2df,2p)//M06-2X/6-31G(d,p) calculations. M06-2X is a recently developed hybrid-meta functional that is parametrized to include the London dispersion energy. The 38T H-FAU and 34T H-ZSM-5 nanocluster models where T atoms are either Si or Al atoms are used to represent H-FAU and H-ZSM-5 zeolites. The adsorption energies of hexane are predicted to be -10.8 and -18.2 kcal/mol for H-FAU and H-ZSM-5, respectively, in good agreement with experimental measurements. This indicates that the confinement effects on different types of zeolites can be well represented by the M06-2X functional. The reaction is assumed to proceed in two steps. In the first step, the central C-C bond of adsorbed n-hexane is protonated to form a hexonium intermediate. The adsorbed 3-C-hexonium is highly unstable and can be rapidly decomposed to produce the products. The first step is found to be the rate-determining step with activation energies of 45.7 and 45.8 kcal/mol for H-FAU and H-ZSM-5, respectively. For step two, the activation energies are calculated to be 8.6 and 9.9 kcal/mol for H-FAU and H-ZSM-5, respectively. The results clearly demonstrate that the reaction of n-hexane cracking is intrinsically the same in these large-and medium-pore zeolites. The different apparent activities can be explained by the different adsorption energies which are mainly due to the van der Waals interactions with the zeolite walls.

Catalytic conversion of hazardous gases can solve many of the environmental problems caused by them. We performed a density functional theory (DFT) study with the Perdew−Burke−Ernzerhof (PBE) functional to investigate the CO oxidation by using N 2 O as an oxidizing agent over an iron-embedded graphene (Fe-Graphene) catalyst. The N 2 O molecule was first decomposed on the Fe site yielding the N 2 molecule and an Fe−O intermediate, which was an active species for the CO oxidation. The activation energy for the N 2 O decomposition step was predicted to be 8 kcal/mol. According to the population analysis, the graphene acted as both the electron withdrawing and donating support to assist the charge transfer between the Fe atom and the probe molecules, which are important for the reaction. The reaction was found to be less facile when the Fe site was first covered by the CO which has a higher adsorption energy than that of the N 2 O (−10.0 vs −33.6 kcal/mol). The reaction proceeded via a concerted transition structure and required an activation energy of 19.2 kcal/mol when the CO was prior adsorbed. Thus, control of the adsorbing molecules over Fe-Graphene might be a key factor for the activity of the catalyst. With the higher catalytic activities of Fe-embedded graphene compared to other typical catalysts, this may open new avenues in searching for oxidation of CO at an economical cost.

The oxidation of CO by NO over metal-organic framework (MOF) M(btc) (M = Fe, Cr, Co, Ni, Cu, and Zn) catalysts that contain coordinatively unsaturated sites has been investigated by means of density functional theory calculations. The reaction proceeds in two steps. First, the N-O bond of NO is broken to form a metal oxo intermediate. Second, a CO molecule reacts with the oxygen atom of the metal oxo site, forming one C-O bond of CO. The first step is a rate-determining step for both Cu(btc) and Fe(btc), where it requires the highest activation energy (67.3 and 19.6 kcal/mol, respectively). The lower value for the iron compound compared to the copper one can be explained by the larger amount of electron density transferred from the catalytic site to the antibonding of NO molecules. This, in turn, is due to the smaller gap between the highest occupied molecular orbital (HOMO) of the MOF and the lowest unoccupied molecular orbital (LUMO)  of NO for Fe(btc) compared to Cu(btc). The results indicate the important role of charge transfer for the N-O bond breaking in NO. We computationally screened other MOF M(btc) (M = Cr, Fe, Co, Ni, Cu, and Zn) compounds in this respect and show some relationships between the activation energy and orbital properties like HOMO energies and the spin densities of the metals at the active sites of the MOFs.

The effect of the intercalated alkaline cations between the adjacent layers of multilayered manganese oxide (MnO) towards the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) was investigated. Li-MnO, Na-MnO, K-MnO, Rb-MnO, and Cs-MnO provide OER overpotentials of 1.64, 1.70, 1.79, 1.83, and 1.84 V vs. RHE, respectively as well as ORR overpotentials of 0.71, 1.06, 1.13, 1.15, and 1.14 V vs. RHE, respectively. Li-MnO shows the highest bifunctional catalytic activity towards both the ORR and OER. In addition, the Gibbs free energy change of *OH adsorption is found to be the largest throughout the reaction pathways determining the rate of the whole ORR and OER.

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Ethanol, through the utilization of bioethanol as a chemical resource, has received considerable industrial attention as it provides an alternative route to produce more valuable hydrocarbons. Using a density functional theory approach incorporating the M06-L functional, which includes dispersion interactions, a large 34T nanocluster model of Fe-ZSM-5 zeolite in which T is a Si or Al atom is employed to examine both the stepwise and concerted mechanisms of the transformation of ethanol into ethene. For the stepwise mechanism, ethanol dehydration commences from the first hydrogen abstraction of the ethanol OH group to form the ethoxide-hydroxide intermediate with a low activation energy of 17.7 kcal mol(-1). Consequently, the ethoxide-hydroxide intermediate is decomposed into ethene through hydrogen abstraction from the ethoxide methyl carbon to either the OH group of hydroxide or the oxygen of the ethoxide group with high activation energies of 64.8 and 63.5 kcal mol(-1), respectively. For the concerted mechanism, ethanol transformation into the ethene product occurs in a single step without intermediate formation, with an activation energy of 32.9 kcal mol(-1).