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 de position has been investigated in the CO + NO reactions from temperature-pr ogrammed experiments performed under stoichiometric conditions. It has been found that the activity of ZrxCe1-xO2 depends on either the specific surfa ce area or the number of Ce cations and their intrinsic activity, Zr0.5Ce0. 5O2 being the most active support. The addition of palladium strongly enhan ces the catalytic activity of the supports probably due to a synergistic ef fect between CeO2 and the metal since the initial activity of palladium-bas ed catalysts is directly related to their Ce content. Such a catalytic enha ncement has been explained by a "bifunctional" mechanism involving active s ites probably composed of I'd and ceria. A strong deactivation operates lea ding to the disappearance of the beneficial effect of ceria. Such a deactiv ation seems to be dependent on the support composition, Pd supported Zr0.25 Ce0.75O2 being the most resistant to deactivation.