Stability of cobalt supported on ZrO2 catalysts for methane combustion

Cobalt supported catalysts were prepared by two different techniques: atomic layer epitaxy (ALE) and wet impregnation. Either ZrO2 or La/ZrO2 (La-doped ZrO2) were used as supports. The solids were characterized by XRD, TPR and XPS before and after hydrothermal and catalytic stability tests (TOS: 150 h, 970 K). The most active catalysts were those in which cobalt was incorporated using the epitaxial growth technique. Moreover, the initial activity of cobalt supported on ZrO2 by ALE was significantly higher than that on La/ZrO2. But, after maintaining the former catalysts for 150 h at 970 K on stream (stability test), their initial high activities significantly decreased. On the other hand, when Co was supported on La-doped ZrO2 the resulting catalysts became much more stable. Combining the catalytic results with the characterization information a simple model is proposed that rationalizes the behavior of these solids.