An ab Initio Study on the Oxidative Coupling of Methane over a Lithium-Doped MgO Catalyst:  Surface Defects and Mechanism

Abstract

We present a study on the catalytic cycle responsible for coupling of methane by molecular oxygen over a lithium-doped magnesium oxide catalyst. To elucidate the mechanism by which methyl radicals are produced and the active sites are regenerated, geometries and energies of relevant reaction intermediates were determined using an ab initio embedded cluster model. Our results suggest a new mechanism that requires only one active site and does not involve the energetically costly process of creating lattice vacancies. This mechanism is more consistent with the available experimental data than the Ito-Lunsford mechanism proposed earlier.

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

“…1 The partial oxidation and oxidative coupling of methane, in particular, have attracted considerable attention. [2][3][4][5][6][7][8][9] Many metal oxide catalysts have been used for these reactions, 2,[10][11][12] and MgO has been found to be one of the most effective catalysts. 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.…”

“…18 The rate-determining step in the conversion of methane to higher derivatives has been shown to be the abstraction of hydrogen at the surface. 4 To obtain further information about this process, many theoretical studies of the interaction of methane with metal oxide heve been performed using an oxometal cluster model 9,16,[18][19][20][21] and gaseous metal oxide molecules. [22][23][24][25][26][27] Of particular interest is the direct oxidation of methane by metal oxide fragments, [22][23][24][25][26][27] because this process can be justifiably regarded as providing models for the more complicated processes of heterogeneous or enzymatic methane monooxygenase catalysis.…”

Dissociation of Water at the MgO(100)−Water Interface: Comparison of Theory with Experiment

“…This electron spectroscopic technique provides superior surface sensitivity and allows for direct imaging of the local density of occupied states on the surface (see ref 21 for a review). In addition, ab initio calculations were performed using the CECILIA model 22,23 (combined embedded cluster at the interface with liquid approach), which is the combination of an embedded cluster model 24,25 for representing interactions of the surface active site with the crystal lattice and the use of a dielectric continuum to model long-range polarization of the solvent. All computational conditions, i.e., cluster and embedding lattice size, pseudopotentials, basis sets, parameters of the solvation model, etc., are identical to those used in a recently published article 26 (referred to in this paper as article 1), so they will be repeated here only to the extent necessary for unity.…”

A new nano‐(2Li2O/MgO) catalyst/porous alpha‐alumina composite for the oxidative coupling of methane reaction

“…For example, lithium-doped MgO is an effective catalyst for the oxidative coupling of methane (OCM). 1 On the other hand, such catalyst particles should be located on the external surface of nonporous or internal surface of porous carriers. The latter is of most importance, as the OCM reaction using porous ceramic membrane catalytic reactors has opened a new horizon in this area.…”