Model bimetallic Pd-Ni automotive exhaust catalysts: Influence of thermal aging and hydrocarbon self-poisoning

Bimetallic Pd-Ni catalysts supported on Al2O3 and (Ce,Zr)Ox/Al2O3 were examined with respect to their catalytic performance for the elimination of CO, NO and C3H6 under stoichiometric conditions. The effects of a thermal aging treatment at 1273 K, reactant competition in the presence of the hydrocarbon and the influence of the presence of nickel in the catalyst have been analysed by XRD, HREM, catalytic activity measurements and in situ DRIFTS spectroscopy. Self-poisoning effects, induced by the presence of the hydrocarbon in the reactant mixture, were identified as the main factor affecting the light-off activity. While a Ni-induced preferential interaction between Pd and the Ce-Zr mixed oxide component appears, in general terms, to be beneficial for the catalytic performance of the fresh (Ce,Zr)Ox/Al2O3-supported bimetallic catalyst, it is shown to be detrimental for the aged system as a consequence of a facilitated degradation of the (Ce,Zr)Ox component and encapsulation of the active palladium particles.