Effect of the reduction temperature on the catalytic activity of Pd-supported catalysts

Four catalysts (0.58%Pd/Al2O3, 2.1%Pd/CeO2, 7%Pd/Al2O3 and 7%Pd/Ce0.8Tb0.2Ox/La2O3-Al2O3) were prepared by the incipient wetness impregnation method using aqueous solutions of Pd(NH3)4(NO3)2 and Pd(NO3)2. In all cases, the metallic loading was referred to as 100 g of support. The catalysts were characterized by XRD, temperature-programmed reduction (TPR) and surface area. The catalytic activity was measured using the methane combustion at 300 °C. The presence of large PdO particles was verified by the diffraction peak observed at 33.8° in the catalysts. TPR results for the 2.1%Pd/CeO2 catalyst showed that the decoration effect of Pd by the support increased with the reduction temperature. The catalytic activity results revealed that the nature of the PdOx active phase strongly depended on both the reduction treatment and the oxygen partial pressure. The conversions for catalysts 2.1%Pd/CeO2 (71%), 7%Pd/Al2O3 (79%) and 7%Pd/Ce0.8Tb0.2Ox/La2O3-Al2O3 (80%) were higher than that of catalyst 0.58%Pd/Al2O3 (14%).