Abstract

In this work, the activity of the catalysts 7%Pd/Ce0.8Tb0.2Ox/La2O3-Al2O3; 7%Pd/Al2O3; 0.58%Pd/Al2O3 and 2.1%Pd/CeO2 were tested by means of the methane combustion reaction. The catalysts were prepared by the wet impregnation method using two different aqueous solutions of Pd(NH3)4(NO3)2. In all the cases, the metallic loading was referred to 100 g of support. The 2.1%Pd/CeO2 catalyst was prepared at the Cadiz University-Spain. The catalysts were studied by XRD, surface area and temperature programmed reduction (TPR). The diffraction signal observed at 33.8° in the catalyst with 7% of Pd, verified the presence of large PdO particles. The specific area of the catalysts 2.1% Pd/CeO2; 7%Pd/Al2O3 and 7%Pd/Ce0.8Tb0.2Ox/La2O3-Al2O3 were 64.4; 122.1 and 79.4 m2 g-1, respectively. TPR results for the 2.1%Pd/CeO2 catalyst showed that the decoration effect of the Pd by the support increased with a reduction temperature higher than 500 °C. The presence of the beta-hydride phase suggests low metal dispersion. Based on the catalytic activity, the nature of the PdOx active phase depends strongly with the reduction treatment and oxygen partial pressure. The total regeneration of the 2.1%Pd/CeO2 catalyst could indicates that electronic effects between Pd and the support only caused the initial deactivation. The high conversions registered for 7%Pd/Al2O3 catalyst compared with the 0.58%Pd/Al2O3 confirmed that high palladium loading favors the methane combustion reaction. Finally, the pH of the impregnant solution did not affect the catalytic performance of the catalysts.