Theoretical Investigation of the Selective Oxidation of Methane to Methanol on Nanostructured Fe‐ZSM‐5 by the ONIOM Method

Pantu, Piboon; Pabchanda, Suwat; Limtrakul, Jumras

doi:10.1002/cphc.200400156

Cited by 57 publications

(75 citation statements)

References 51 publications

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“…Hence, small quantum cluster calculations which basically neglect these interactions can give erroneous results. However, hybrid methods such as QM/MM and ONIOM can reasonably describe these interactions [12][13][14][15] with only a small increase in computational demand. Therefore, we used the ONIOM method to investigate ethylene dimerization inside faujasite zeolite.…”

Section: Resultsmentioning

confidence: 99%

“…The recent development of hybrid methods, such as embedded cluster or combined quantum mechanics/molecular mechanics (QM/MM) methods, as well as the more general ONIOM (our own n-layered integrated molecular orbital and molecular mechanics) method [11] has brought obtaining accurate results on larger systems within reach. Recent theoretical studies [12][13][14][15] have shown that the ONIOM scheme can be efficiently used for characterizing the reactivity of active sites inside zeolites.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

2005

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Ethylene dimerization was investigated by using an 84T cluster of faujasite zeolite modeled by the ONIOM3(MP2/6-311++G(d,p):HF/6-31G(d):UFF) method. Concerted and stepwise mechanisms were evaluated. In the stepwise mechanism, the reaction proceeds by protonation of ethylene to form the surface ethoxide and then C--C bond formation between the ethoxide and the second ethylene molecule to give the butoxide product. The first step is rate-determining and has an activation barrier of 30.06 kcal mol(-1). The ethoxide intermediate is rather reactive and readily reacts with another ethylene molecule with a smaller activation energy of 28.87 kcal mol(-1). In the concerted mechanism, the reaction occurs in one step of simultaneous protonation and C--C bond formation. The activation barrier is calculated to be 38.08 kcal mol(-1). Therefore, the stepwise mechanism should dominate in ethylene dimerization.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

2005

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“…Among the numerous competing active sites in Fe/ZSM-5 zeolite, the mono-iron species has been the most extensively studied [34][35][36][37][38][39][40][41][42]. It is probably due to two reasons.…”

Section: The Mono-iron Speciesmentioning

confidence: 98%

Active Sites in Fe/ZSM-5 Zeolite

et al. 2010

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Fe/ZSM-5 zeolite has shown great potential in the selective oxidations of hydrocarbons such as methane and benzene. The various competing active sites of Fe/ ZSM-5 zeolite are reviewed, including the mono-iron, oxygen-bridged [Fe, X] (X = Fe, Al) and peroxide species; in addition, the influences of H 2 pretreatment are considered. For the mono-iron species, the H 2 molecules are chemisorbed on the Fe(III) sites via the g 2 -binding mode. Both high-and low-spin Fe(III) ions play an important role during the H 2 reduction process whereas the former predominates in the N 2 O decomposition process. As the calculated energy barriers indicate, the Fe(III) ions are facile to be reduced by H 2 pretreatment and therefore the active site of the mono-iron species should be in the FeO(OH) form. Instead, the oxygen-bridged [Fe, X] and peroxide species remain stable by H 2 pretreatment. The suitable oxygenbridged [Fe, X] structures are screened out by comparisons with the experimental data and energy considerations from computational aspects. The geometries are in good agree-

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“…The cluster model is similar to that used in our previous study on isolated metal oxide on zeolite. [12] The [VO 2 ] ionic group lies between the two bridging oxygen atoms of the zeolite framework forming a tetrahedral arrangement at the vanadium atom, which is the most stable configuration. With the M06-L functional and the 6-31G(d,p) basis set, the optimized VÀO bond lengths are 1.59, 1.59, 1.98, and 1.98 for VÀO1, VÀO2, VÀOa, and VÀOb, respectively.…”

Section: Propane Adsorption Over the Catalystmentioning

confidence: 99%

Oxidative Dehydrogenation of Propane over a VO₂‐Exchanged MCM‐22 Zeolite: A DFT Study

et al. 2010

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The adsorption and the mechanism of the oxidative dehydrogenation (ODH) of propane over VO(2)-exchanged MCM-22 are investigated by DFT calculations using the M06-L functional, which takes into account dispersion contributions to the energy. The adsorption energies of propane are in good agreement with those from computationally much more demanding MP2 calculations and with experimental results. In contrast, B3LYP binding energies are too small. The reaction begins with the movement of a methylene hydrogen atom to the oxygen atom of the VO(2) group, which leads to an isopropyl radical bound to a HO-V-O intermediate. This step is rate determining with the apparent activation energy of 30.9 kcal mol(-1), a value within the range of experimental results for ODH over other silica supports. In the propene formation step, the hydroxyl group is the more reactive group requiring an apparent activation energy of 27.7 kcal mol(-1) compared to that of the oxy group of 40.8 kcal mol(-1). To take the effect of the extended framework into account, single-point calculations on 120T structures at the same level of theory are performed. The apparent activation energy is reduced to 28.5 kcal mol(-1) by a stabilizing effect caused by the framework. Reoxidation of the catalyst is found to be important for the product release at the end of the reaction.

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Theoretical Investigation of the Selective Oxidation of Methane to Methanol on Nanostructured Fe‐ZSM‐5 by the ONIOM Method

Cited by 57 publications

References 51 publications

Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

Active Sites in Fe/ZSM-5 Zeolite

Oxidative Dehydrogenation of Propane over a VO₂‐Exchanged MCM‐22 Zeolite: A DFT Study

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Theoretical Investigation of the Selective Oxidation of Methane to Methanol on Nanostructured Fe‐ZSM‐5 by the ONIOM Method

Cited by 57 publications

References 51 publications

Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

Active Sites in Fe/ZSM-5 Zeolite

Oxidative Dehydrogenation of Propane over a VO2‐Exchanged MCM‐22 Zeolite: A DFT Study

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Oxidative Dehydrogenation of Propane over a VO₂‐Exchanged MCM‐22 Zeolite: A DFT Study