Pd-Ni catalysts supported on Al2O3, (Ce,Zr)O-X/Al2O3, and (Ce,Zr)O-X, were examined with the principle objective of determining the effects of Ni on catalytic activity for CO oxidation and NO reduction reactions under stoichiometric conditions. Catalytic activity findings for the CO + O-2 and CO + O-2 + NO reactions were analyzed in conjunction with in situ DRIFTS and XANES results to obtain information on the processes occurring in the catalysts during the course of the reactions. The results reveal a significant dependence on the nature of the support in terms of the catalytic changes produced by nickel. In the absence of significant nickel-induced electronic perturbations of palladium, these are related to indirect effects on palladium distribution over the catalysts or to a certain impediment of the interactions between active palladium and Ce-Zr mixed-oxide components. Significant promotion of CO oxidation was observed for the (Ce,Zr)O-X/Al2O3-supported catalyst, which reveals a relevant role for the particle size of the nanostructured Ce-Zr mixed oxide in this reaction. (c) 2005 Elsevier Inc. All rights reserved.