Catalytic reforming of methane with carbon dioxide on reduced perovskite-type oxides

The reforming reactions of CH4 with CO2 diluted with He were carried out over the cobalt catalysts prepared from the perovskite structural oxides, LnCoO(3) (Ln = La, Pr, Nd, Sm, Eu, Gd, Er, Tb) and the relationship between the reaction activity and the surface properties of the catalysts were examined. The reaction activity at 873 K of the catalysts containing the rear earth element of higher atomic number than Eu was remarkably higher than that of the catalysts having lower atomic number than Eu. The surface properties of the Co/La2O3, Co/Sm2O3 and Co/Eu2O3 catalysts decomposed from LaCoO3, SmCoO3 and EuCoO3 were particularly examined. EuCoO3 was reduced much easier to metallic cobalt and europium oxide than LaCoO3 and SmCoO3. The decomposed products by reduction were led to the catalyst with high activity. On the other hand, LaCoO3 and SmCoO3 were not fully and easily reduced and very small amount of cobalt oxides remained on the surface. The difficulty of reducibility of LaCoO3 and SmCoO3 caused the lost or low activity. The decomposed Co/Eu2O3 catalyst had two kinds of active sites which operated at relatively low (873 K) and high temperature (1073 K) regions. The other two kinds of catalysts had only one active site which operated at high temperature. This caused the lost or low activity at low temerature such as 873 K in the case of the latter. Especially the decomposed Co/La2O3 catalyst had a strong affinity to CO2 and easily produced a lanthanum carbonate which was decomposed at high temperature (> 973 K). The formation of the carbonate inhibited the reaction, probably by the oxidation of the metallic cobalt on the catalyst surface.