Activation of Methane on the MgO Surface at Low Temperatures

Ito, Tairo; Tashiro, Toshihiko; Watanabe, Tomoko; Toi, Keio; Ikemoto, Isao

doi:10.1246/cl.1987.1723

Cited by 28 publications

(20 citation statements)

References 9 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…For comparison, we report our HSE(0.3)+vdW results also for this case. The CH 4 molecule breaks to H + , which binds to the O anion, and anionic CH 3 – bonds to the Mg cation. , We considered such dissociative adsorption at the step site. Our calculations for the pristine MgO show that such process is endothermic with Δ r E = +0.10 eV, the equilibrium C–Mg and O–H distances are 2.19 and 0.97 Å, respectively.…”

Section: Resultsmentioning

confidence: 99%

Ni Substitutional Defects in Bulk and at the (001) Surface of MgO from First-Principles Calculations

Mazheika

Levchenko

2016

J. Phys. Chem. C

View full text Add to dashboard Cite

Computational detailsCCSD(T) calculations of CO, CO 2 , and H 2 adsorption energies at Ni Mg defects at the MgO(001) surface, as well as formation energies of bulk Ni Mg , are performed using ORCA electronic-structure package, which is based on Gaussian-type orbitals [1]. For bulk Ni Mg defects, NiMg 12 O 6 (PP) 50 cluster is used (Fig. 1c in main ). 14 electrons are removed to ensure bulklike ionization states of all the atoms. The positions of the atoms, ECPs, and point charges in the bulk cluster models are generated by cutting out a cube centered on a Mg atom from the bulk MgO structure with 4.211 Å) lattice constant, with no further relaxation. The lattice constant was obtained from standard HSE06 calculations (see below for details). For surface Ni Mg defects, two models were used: terrace-site and monolayer-step ( Fig. 1a-b in main text), both have the stoichiometry NiMg 8 O 9 (PP) 49 . The structure of the terrace-site cluster was generated as follows. First, a periodic slab model of MgO (001) (2x2 surface unit cell and 4 atomic layers) with a Ni Mg defect and possibly an adsorbed molecule is relaxed at HSE06 level with tight basis set and 4x4x4 k-points. Second, the cluster around the Ni Mg defect was cut out of the slab and immersed into an array of point charges and pseudopotentials. The geometry of embedding corresponded to ideal bulk-like structure. Since the relaxation of (sub)surface atomic layers is pronounced very slightly even with Ni, such embedding geometry matches cluster structure well. In the case of monolayer-step cluster, similar strategy was applied. The 4-atomic layer MgO(001) slab (2x3 surface unit cell) with a periodically translated along x-axe (2x2) "monolayerisland" and with/without adsorbate molecule was fully relaxed at HSE06 level. The cluster with Ni Mg defect was cut from it and embedded like in the other cases. For all cluster models, the target properties were converged with respect to the number of shells of pseudopotentials and point charges at PBE level. Collinear spin-unrestricted calculations are performed, unless otherwise specified, with spinmoment projection fixed to S z = 1, which is found to be the ground spin-state of the neutral Ni Mg defect for all α. The spin-states of charged defects are discussed in the main text.In the CCSD(T) calculations, cc-pVXZ [3] basis sets are employed, with X = D for Mg and O, and X = T for all atoms in adsorbed species and surface atom underneath (Ni or O). For adsorption and defect formation energies, counterpoise basis-set superposition error (BSSE) correction is applied. The excitations from 1s-3p orbitals of Ni, 1s-2p of Mg, 1s of O and C were excluded from the coupledcluster calculations (frozen-core approximation). These settings were the best we could afford with our embedded cluster models. However, we estimate the complete basis-set (CBS) limit for CCSD(T) by combining the extrapolation of MP2 energies to CBS limit with the so-called "focal-point" method [4] which is based on the observation that the difference in correl...

show abstract

Section: Resultsmentioning

confidence: 99%

Ni Substitutional Defects in Bulk and at the (001) Surface of MgO from First-Principles Calculations

Mazheika

Levchenko

2016

J. Phys. Chem. C

View full text Add to dashboard Cite

show abstract

“…Since lithium-doped magnesia was reported as an effective catalyst for methane coupling by Lunsford and his co-workers as mentioned above [17,18], alkali-doped alkaline earth metal oxides have been studied by many investigators [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35]. The unpromoted oxides of the alkaline earth metals are themselves active for oxidative coupling of methane [23][24][25][26][27]. Doping with a proper alkali metal, however, increases the conversion and selectivity significantly.…”

Section: Alkali and Alkaline Earth Metalsmentioning

confidence: 99%

“…which also shows some activity. By using TPD and EPR spectroscopy Ito et al [27] reported that MgO could activate methane even below room temperature by dissociatively adsorbing methane heterolytically on the sites of O^c -Mg^ and Ox-Mg4c-. These ion pairs are in low coordination states on MgO, but their participation in the methane coupling reaction at high temperatures remains to be proved.…”

Section: A Catalystsmentioning

confidence: 99%

Conversion of Methane by Oxidative Coupling

et al. 1990

View full text Add to dashboard Cite

“…12,13 To understand the nature of the interaction between methane and MgO, the adsorption and dissociation of methane on MgO catalyst have been extensively investigated experimentally. [2][3][4][5][6][10][11][12][13][14][15][16][17][18] In 1985, Driscoll and co-workers 10,11 found that when methane is passed over MgO at temperatures above 800 K, CH 3 • radicals are formed, then released into the gas phase, and detected after collection in an argon matrix. Later, Ito and co-workers 15,16 proposed that methane pretreated above 973 K on MgO could be adsorbed in a heterolytically dissociated form, CH 3 -on Mg 2+ and H + on O 2-, even below room temperature.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Study on the Mechanism of the Reaction of CH₄ + MgO

Yang

Wong

et al. 2003

J. Phys. Chem. A

View full text Add to dashboard Cite

The reactions of (1) CH 4 + MgO f MgOH• + CH 3 • and (2) CH 4 + MgO f Mg + CH 3 OH have been studied on the singlet spin state potential energy surface at the MP2/6-311+G(2d,2p) level. These two reaction channels, both involving intermediates and transition states, have been rationalized by the structures of the species involved, natural bond orbital (NBO), and vibrational frequency analysis. We have considered two initial interacting models between CH 4 and MgO: a collinear C-H approach to the O end of the MgO forming the MgOCH 4 complex with C 3V symmetry and three hydrogen atoms of the methane point to the Mg end of the MgO forming the OMgCH 4 complex with C 1 symmetry. The calculations predict that reactions 1 and 2 are exothermic by 39.8 and 86.5 kJ mol -1 , respectively. Also, the former reaction proceeds more easily than the latter, and the complex HOMgCH 3 is energetically preferred in the reaction of MgO + CH 4 .

show abstract

Activation of Methane on the MgO Surface at Low Temperatures

Abstract: The C–H bond of methane is easily activated on the MgO surface even below room temperature. Active sites consist of intrinsic ion pairs, O3C2−–Mg3C2+ and O4C2+, of MgO in low coordination states on which a methane molecule adsorbs in heterolytically dissociated form.

Cited by 28 publications

References 9 publications

Ni Substitutional Defects in Bulk and at the (001) Surface of MgO from First-Principles Calculations

Ni Substitutional Defects in Bulk and at the (001) Surface of MgO from First-Principles Calculations

Conversion of Methane by Oxidative Coupling

Theoretical Study on the Mechanism of the Reaction of CH₄ + MgO

Contact Info

Product

Resources

About

Activation of Methane on the MgO Surface at Low Temperatures

Abstract: The C–H bond of methane is easily activated on the MgO surface even below room temperature. Active sites consist of intrinsic ion pairs, O3C2−–Mg3C2+ and O4C2+, of MgO in low coordination states on which a methane molecule adsorbs in heterolytically dissociated form.

Cited by 28 publications

References 9 publications

Ni Substitutional Defects in Bulk and at the (001) Surface of MgO from First-Principles Calculations

Ni Substitutional Defects in Bulk and at the (001) Surface of MgO from First-Principles Calculations

Conversion of Methane by Oxidative Coupling

Theoretical Study on the Mechanism of the Reaction of CH4 + MgO

Contact Info

Product

Resources

About

Theoretical Study on the Mechanism of the Reaction of CH₄ + MgO