A Critical Assessment of Li/MgO-Based Catalysts for the Oxidative Coupling of Methane

Arndt, Sebastian; Laugel, Guillaume; Levchenko, Sergey V.; Horn, Raimund; Baerns, M.; Scheffler, Matthias; Schlögl, Robert; Schomäcker, Reinhard

doi:10.1080/01614940.2011.613330

Cited by 217 publications

(205 citation statements)

References 316 publications

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“…It was suggested by Ito and Lunsford in 1985 that in Li-MgO, activated surface oxygen species are produced by substituting divalent Mg with monovalent Li ions, generating electron holes in the oxygen electronic bands. It was further assumed that electron transfer from methane into these low-lying hole states triggers the abstraction of a H atom from the adsorbate as the initial step for subsequent coupling reactions of the remaining CH 3 units to longer hydrocarbons [1]. Although put forward long ago, this mechanism for the oxidative coupling of methane still poses a number of questions, both from the experimental and theoretical viewpoints [2][3][4].…”

Section: Introductionmentioning

confidence: 99%

Defect complexes in Li-doped MgO

et al. 2015

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Magnesium oxide (MgO) is used in a variety of industrial applications due to its low cost and structural stability. In heterogeneous catalysis, MgO and Li-doped MgO have been studied as catalysts for the oxidative coupling of methane. In this work, we analyze the structure and stability of defect complexes comprising Li dopants and oxygen vacancies in MgO, combining scanning tunneling microscopy, photon-emission experiments, and density-functional theory computations. The experimental results strongly indicate that after annealing Li-doped MgO to temperatures of 600 K and higher, Li evaporates from the surface, but Li defects, such as substitutional defects, interstitials, or defect complexes comprising Li remain in the bulk. Our calculations show that bulk defect complexes containing F 2+ color centers, that have donated their two electrons to two adjacent Li defects, are the most stable configurations at realistic pressure and temperature conditions.

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Section: Introductionmentioning

confidence: 99%

Defect complexes in Li-doped MgO

et al. 2015

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“…Recently, OCM research has gained momentum again. Li/ MgO was reviewed [66] and studied again in great detail but neither experiment nor theory gave evidence that Li þ O À exists under OCM conditions [67]. Both on a Li-doped MgO film grown on a Mo(001) substrate but also on Li-doped MgO powders surface segregation of Li was observed above 700 K and Li-desorption above 1,050 K. Figure 9 shows the surface of such a Li-doped MgO-film upon heating to 700 and 1,050 K. The formation of Li-rich surface oxides patches and the rectangular surface defects left behind upon Lidesorption are clearly seen and in line with ab-intio thermodynamic calculations [67].…”

Section: Ocm With Dioxygenmentioning

confidence: 99%

Methane Activation by Heterogeneous Catalysis

2014

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Methane activation by heterogeneous catalysis will play a key role to secure the supply of energy, chemicals and fuels in the future. Methane is the main constituent of natural gas and biogas and it is also found in crystalline hydrates at the continental slopes of many oceans and in permafrost areas. In view of this vast reserves and resources, the use of methane as chemical feedstock has to be intensified. The present review presents recent results and developments in heterogeneous catalytic methane conversion to synthesis gas, hydrogen cyanide, ethylene, methanol, formaldehyde, methyl chloride, methyl bromide and aromatics. After presenting recent estimates of methane reserves and resources the physico-chemical challenges of methane activation are discussed. Subsequent to this recent results in methane conversion to synthesis gas by steam reforming, dry reforming, autothermal reforming and catalytic partial oxidation are presented. The high temperature methane conversion to hydrogen cyanide via the BMA-process and the Andrussow-process is considered as well. The second part of this review focuses on one-step conversion of methane into chemicals. This includes the oxidative coupling of methane to ethylene mediated by oxygen and sulfur, the direct oxidation of methane to formaldehyde and methanol, the halogenation and oxyhalogenation of methane to methyl chloride and methyl bromide and finally the non-oxidative methane aromatization to benzene and related aromates. Opportunities and limits of the various activation strategies are discussed.

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“…It is also an important comparison with other rocksalt compounds such as EuO and LiF. Li doped MgO (MgO:Li) is also useful as a heterogeneous catalyst [4], and aside from chemical doping routes, Li + ion implantation has also been studied recently as a means to modify MgO [5]. In this context, local information on the Li site and defect electronic structure for truly isolated Li + would be a valuable addition to understanding MgO:Li.…”

Section: Introductionmentioning

confidence: 99%