Effect of thermal ageing on the structure and catalytic activity of Pd/CeO2 prepared using arc-plasma process

Pd nanoparticles were deposited onto CeO2 powders using an arc-plasma process in order to study their thermal behaviour and catalytic activity for CO oxidation. As-prepared catalyst exhibited a higher catalytic activity than catalysts prepared via conventional wet-impregnation because the metallic state of Pd responsible for CO oxidation activity is abundant. The activity was decreased by thermal ageing at 600 degrees C in air, which oxidized metallic Pd to the oxide interacting with the surface of CeO2. On the other hand, ageing at 900 degrees C in 10% H2O/air significantly enhanced the activity, regardless of sintering of CeO2, to show the highest activity, as observed in our previous work for the catalyst prepared by conventional wet-impregnation. The activation by thermal ageing is associated with the thermodynamic dissociation of the oxidic Pd to metallic Pd species at 900 degrees C.