545733 Activation of Oxygen - Key to the Oxidative Coupling of Methane (OCM) Reaction

Tuesday, June 4, 2019: 4:00 PM
Texas Ballroom A (Grand Hyatt San Antonio)
Lukas Thum, Dept. of Chemistry, TU Berlin, Berlin, Germany, Prof. Dr. Reinhard Schomäcker, Institute of Chemistry, TU Berlin, Berlin, Germany, Annette Trunschke, Inorganic Chemistry, Fritz Haber Institute, Berlin, Germany and Robert Schlögl, Department of Inorganic Chemistr, Fritz Haber Insitute of the Max Planck Society, Berlin

Activation of Oxygen - Key to the Oxidative Coupling of Methane (OCM) Reaction

Since the 1980's, many materials have been investigated as suitable catalysts for the OCM reaction with mediocre success so far. The major challenge is the direction of the reaction towards the desired higher hydrocarbons while suppressing the thermodynamically favored deep oxidation towards carbon monoxide and carbon dioxide. An apparent yield barrier of 30% has yet to be surpassed.1 Non reducible basic oxides such as alkaline earth oxides as well as rare earth oxides have been found as promising catalyst materials, finding first application in an OCM process by siluria technology. Even though the bond dissociation energy of methane is large with 423 kJ/mol, controlling the activation of oxygen is much more important to direct the selectivity towards the desired products. In case of basic non reducible oxides e.g. CaO the capability of the material to dissociatively activate oxygen appears to be directly linked to the OCM reactivity, making it very likely the bottleneck of the reaction. The strong basicity which is needed for the reaction is also a major weakness of those materials, forming stable hydroxides and carbonates incapable of activating oxygen even at high temperatures. This is not observed with another promising catalyst for the OCM reaction, the Na2WO4/MnxOy/SiO2 system, showing a good overall catalytic performance. With MnxOy as an oxygen reservoir this system also offers the possibility of a chemical looping process concept, showing two major prospects: the absence of gas phase oxygen suppressing gas phase reaction and the control of the oxygen species on the catalysts surface by the removal of weakly adsorbed species.2

References

(1) Zavyalova, U.; Holena, M.; Schlögl, R.; Baerns, M. Statistical Analysis of Past Catalytic Data on Oxidative Methane Coupling for New Insights into the Composition of High-Performance Catalysts. ChemCatChem 2011, 3 (12), 1935–1947.

(2) Fleischer, V.; Simon, U.; Parishan, S.; Colmenares, M. G.; Görke, O.; Gurlo, A.; Riedel, W.; Thum, L.; Schmidt, J.; Risse, T.; et al. Investigation of the role of the Na2WO4/Mn/SiO 2 catalyst composition in the oxidative coupling of methane by chemical looping experiments. J. Catal. 2018, 360, 102–117.


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