Comparison of oxidizing agents for the oxidative coupling of methane over state-of-the-art catalysts

The synthesis of selected state-of-the-art catalysts providing high performances in the oxidative coupling of methane (OCM) with O2 was reproduced according to the respective recipes reported in literature. A reference material with identical stoichiometric composition was further synthesized by applying the cellulose templating method. This method increases the surface area and affects the phase composition and crystallite size of the catalysts as determined by N2-physisoprtion, X-ray diffraction and scanning electron microscopy. This, however, is in most cases detrimental to the catalytic OCM performance due to enhanced global activity resulting in hot spots in the catalyst bed. Catalysts were tested in the OCM under variation of temperature (973–1073 K), GHSV (3600–100,000 h−1) and oxidizing agent (O2 and N2O). In general, conversions of CH4 when using N2O are lower than in the presence of O2, however, the selectivities to C2 products ethane and ethylene are higher even at a similar level of CH4 conversion. This confirms the presence of different oxygen species formed by activation of these oxidizing agents.

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► Besides chemical composition the synthesis strategy is a crucial factor for success in terms of high C2 yields.
► High surface areas obtained with the cellulose templating method are detrimental to C2 selectivity.
► Catalyst recipes and trends in catalytic performances reported in literature can be reproduced in most cases.
► N2O is a milder oxidizing agent than O2 leading to lower CH4 conversions and higher C2 selectivities even at iso-conversion.
► CO2 activation requires high temperatures although thermodynamically favored.