Oxidative coupling of methane over KCl-LnCl3 eutectic molten salt catalysts

Potassium-lanthanide chloride molten salts (KCl-LnCl(3), Ln = La, Ce, Sm, Dy and Yb) were used as catalysts for the oxidation of methane with N2O. They proved to be active and selective for the production of C-2 hydrocarbons (e.g. CH4 conversion approximate to 15% and C-2 selectivity > 75% over the KCl-CeCl3 catalyst at 750 degrees C) and remarkably stable for long periods of time on the gaseous stream (> 48 h). It was also found that their catalytic performance depends on thef block element (increases when La is replaced by Ce,Sm or Dy). The factors that seem to contribute to the variation of the activity and selectivity are the catalysts acid-base properties (higher acidity implies high activity, but lower selectivity to C-2 hydrocarbons) and the oxidative character of the rare earth trivalent ions in the potassium chloride molten melt (high oxidation-reduction potentials implies lower activity and higher selectivity to hydrocarbons). The effect of the type of oxidant was also studied. The potassium-lanthanide chloride molten salts were more selective to hydrocarbons under N2O than under O-2, e.g. approximate to 75 vs. approximate to 40% over KCI-CeCI3, respectively, which is clearly an advantage taking into account that nitrous oxide is a major greenhouse agent. To our knowledge, this is the first time that molten metal chloride catalysts were used as catalysts for the catalytic conversion of methane into hydrocarbons using N2O as oxidant. (C) 2013 Elsevier B.V. All rights reserved.