A treatment with H-2 at 800 degreesC followed by mild reoxidation (<300<degrees>C) increases the low temperature (<200<degrees>C) steady-state activity in the reduction of NO by propene in the presence Of O-2 of a Pt(1.5%)/(ZrO2-CeO2 on Al2O3) catalyst. The effect is not present for a lower temperature treatment with H-2 or for reoxidation above 300 degreesC. Transient reactivity tests together with characterization data (H-2-TPR, O-2 uptake, H-2 chemisorption) indicate that the high temperature reduction modifies the characteristics of ceria-zirconia and induced metal-support interaction effects, both responsible of the enhanced catalytic activity at low temperature.