Catalytic performance of Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ composite oxides for methane combustion: Influence of cataly

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• 作者：L.F. Liotta ; G. Di Carlo ; G. Pantaleo ; G. Deganello
• 关键词：Cobalt oxide ; Ceria ; Ceria– ; zirconia ; Methane combustion ; Textural properties ; Thermal stability
• 刊名：Applied Catalysis B ; Environmental
• 出版年：2007
• 期刊代码：4_09263373
• 类别：ce
• 出版时间：31 January 2007
• 卷：70
• 期：1-4
• 页码：314-322
• 文件大小：597 K

摘要

The influence of catalyst pre-treatment temperature (650 and 750 °C) and oxygen concentration (λ = 8 and 1) on the light-off temperature of methane combustion has been investigated over two composite oxides, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ containing 30 wt.%of Co₃O₄. The catalytic materials prepared by the co-precipitation method were calcined at 650 °C for 5 h (fresh samples); a portion of them was further treated at 750 °C for 7 h, in a furnace in static air (aged samples).

Tests of methane combustion were carried out on fresh and aged catalysts at two different WHSV values (12 000 and 60 000 mL g⁻¹ h⁻¹). The catalytic performance of Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ were compared with those of two pure Co₃O₄ oxides, a sample obtained by the precipitation method and a commercial reference. Characterization studies by X-ray diffraction (XRD), BET and temperature-programmed reduction (TPR) show that the catalytic activity is related to the dispersion of crystalline phases, Co₃O₄/CeO₂ and Co₃O₄/CeO₂–ZrO₂ as well as to their reducibility. Particular attention was paid to the thermal stability of the Co₃O₄ phase in the temperature range of 750–800 °C, in both static (in a furnace) and dynamic conditions (continuous flow). The results indicate that the thermal stability of the phase Co₃O₄ heated up to 800 °C depends on the size of the cobalt oxide crystallites (fresh or aged samples) and on the oxygen content (excess λ = 8, stoichiometric λ = 1) in the reaction mixture. A stabilizing effect due to the presence of ceria or ceria–zirconia against Co₃O₄ decomposition into CoO was observed.

Moreover, the role of ceria and ceria–zirconia is to maintain a good combustion activity of the cobalt composite oxides by dispersing the active phase Co₃O₄ and by promoting the reduction at low temperature.