(617ct) Theoretical Study on Oxidative Coupling of Methane Using MgO

Authors: 
AlJama, H., Stanford University
Yoo, J. S., Stanford University
Kulkarni, A. R., Georgia Institute of Technology
Latimer, A. A., Stanford University
Abild-Pedersen, F., SLAC National Accelerator Laboratory
Norskov, J. K., SUNCAT Center for Interface Science and Catalysis, Stanford University and SLAC National Accelerator Laboratory
The recent surge in natural gas production, fueled by the exploitation of shale gas reserves, is providing an abundant supply of methane. Tapping into this supply by converting methane into higher value chemicals can significantly impact the chemical industry by adding new supplies of raw materials. However, methane activation remains a major challenge. It is difficult to break the strong and localized C-H bond. In the event the bond is broken, it leads to products more reactive than methane, making it challenging to terminate at desired products without going to complete combustion products. Oxidative coupling of methane offers the potential of selectively converting methane to ethane/ethylene.

The work of Ito and Lunsofrd [1] ignited the interest in this field when they showed that Li-doped MgO can produce ethane/ethylene from methane. The recent surge of natural gas production renewed the interest in this field. Much of the work has focused on the impact of Li-doping on MgO activity. Recently, it was suggested that the effect of Li-doping on MgO is mainly exposing under-coordinated sites that are more reactive. Schwach et al. [2] showed that MgO in its pure form can have appreciable activity, and that MgO morphology can greatly impact its reactivity. Despite much experimental and theoretical work on the subject, there are still many open questions. In this work, we attempt to answer some of these questions. We utilize Density Functional Theory (DFT) to study the impact of surface geometry. We also investigate dopant effect on MgO activity. BEEF-vdw exchange correlation functional is used. Results suggest that surface geometry can have a pronounced effect on methane activation. Developed scaling relations show that hydrogen binding can be used a descriptor to understand the activation process.

[1] Ito, T. Lunsford, J. Synthesis of ethylene and ethane by partial oxidation of methane over lithium-doped magnesium oxide Nature 314 (1985) 721 - 722

[2] Schwach, P. Frandsen, W. Willinger, M. Schlögl, R. Trunschke, R. Structure sensitivity of the oxidative activation of methane over MgO. Journal of Catalysis 329 (2015) 560â??573

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