Investigation of the intrinsic activity of ZrxCe1-xO2 mixed oxides in the CO plus NO reactions:: influence of Pd incorporation

The intrinsic activity of various ZrxCe1-xO2 Mixed oxides and after a Id deposition has been investigated in the CO + NO reactions from temperature-programmed experiments performed under stoichiometric conditions. It has been found that the activity of ZrxCe1-xO2 depends on either the specific surface area or the number of Ce cations and their intrinsic activity, Zr0.5Ce0.5O2 being the most active support. The addition of palladium strongly enhances the catalytic activity of the supports probably due to a synergistic effect between CeO2 and the metal since the initial activity of palladium-based catalysts is directly related to their Ce content. Such a catalytic enhancement has been explained by a "bifunctional" mechanism involving active sites probably composed of I'd and ceria. A strong deactivation operates leading to the disappearance of the beneficial effect of ceria. Such a deactivation seems to be dependent on the support composition, Pd supported Zr0.25Ce0.75O2 being the most resistant to deactivation.