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

Branco, Joaquim B.; Ferreira, Ana C.; Rego, Ana M. Botelho do; Ferraria, Ana M.; Lopes, Gonçalo; Gasche, Teresa A.

Key information

Authors:

Branco, Joaquim B. (Joaquim Miguel Badalo Branco); Ferreira, Ana C. (Ana Cristina Gomes Ferreira da Silva Parreira); Rego, Ana M. Botelho do (Ana Maria Pereira Lopes Redondo Botelho do Rego); Ferraria, Ana M. (Ana Maria da Conceição Ferraria); Lopes, Gonçalo; Gasche, Teresa A. (Maria Teresa Oliveira de Almeida Gasche)

Published in

12/08/2013

Abstract

Potassium-lanthanide chloride molten salts (KCl–LnCl3, 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 C2 hydrocarbons (e.g. CH4 conversion ≈ 15% and C2 selectivity N 75% over the KCl–CeCl3 catalyst at 750 °C) and remarkably stable for long periods of time on the gaseous stream (N48 h). It was also found that their catalytic performance de- pends on the f 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 C2 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 selec- tivity to hydrocarbons). The effect of the type of oxidant was also studied. The potassium-lanthanide chloride mol- ten salts were more selective to hydrocarbons under N2O than under O2, e.g. ≈75 vs. ≈40% over KCl–CeCl3, 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.