Methanation of CO2 over Cobalt-Lanthanide Aerogels: Effect of Calcination Temperature

Abstract

High surface area cobalt-lanthanide bimetallic aerogels were successfully synthesized by the epoxide addition method. The bimetallic aerogels were calcined at two different temperatures and either bimetallic oxides containing oxychlorides, Co3O4.3LnOCl (Ln = La, Sm, Gd, Dy and Yb) or perovskites, LnCoO3 (Ln = La, Sm, Gd and Dy) were obtained at 500 or 900 °C, respectively. The exceptions are the aerogels of cerium and ytterbium, which after oxidation at 500 and 900 °C, stabilize as sesquioxides: Co3O4.3CeO2 and 2Co3O4.3Yb2O3, the first at both temperatures and the second only at the highest temperature. The bimetallic cobalt-lanthanide oxychlorides or perovskites were tested as catalysts for the methanation of CO2. The cobalt catalytic activity is determined by the type and acid-base properties of the lanthanide oxide phase and by its pre-reduction under hydrogen. The best results were those obtained over the calcined aerogels pre-reduced under hydrogen. In particular, the highest values were those obtained over the Co-Ce aerogel calcined at 900 °C that in the same conditions present an activity comparable to that measured over a 5 wt.% Rh catalyst supported on alumina, one of the literature references. The activity and the selectivity increase with the catalysts’ basicity, showing an inverse dependence of the reduction temperature that decreases along the lanthanide series either for the aerogels calcined at 500 or 900 °C. In general, the basicity of the aerogels calcined at 900 °C (perovskites) is higher and they are more active but less selective than those calcined at 500 °C (oxychlorides), which to our knowledge is for the first time reported for the methanation of CO2.