Effect of hydrothermal ageing on the performance of Ce-promoted PdO/ZrO2 for methane combustion

The performance of different Ce-modified PdC/ZrO2 catalysts for methane oxidation in lean mixtures (5000 ppm of CH4) in presence of external water has been studied in this work. Deactivation experiments carried out in presence of 20,000 ppm of external water showed that water reversibly inhibits the reaction. However, it was observed that these catalysts can increase their activity in presence of water at low temperature (350 degrees C). In order to explain this behaviour, different samples of this catalyst were treated with wet air (20,000 ppm of H2O for 30 h). After this pre-treatment, their activity and stability for methane combustion were studied by recording light-off curves for the fresh catalysts and the catalyst after 50 h on stream for the oxidation of methane at 500 degrees C. As general trend, the hydro-ageing at the lowest temperature (300 degrees C) leaded to a very active catalyst (similar activity than the parent one), but it was more markedly deactivated. Hydro-ageing of the catalyst at higher temperatures enhanced its thermal stability. (C) 2008 Elsevier B.V. All rights reserved.