The catalytic activity of Rh/CeO2-ZrO2 for NO reduction by C3H6 under stoichiometric conditions was found to depend strongly on the Ce/Zr composition. Rh/CeO2-ZrO2 with a Ce/Zr molar ratio of 50/50 (Rh/CZ-50/50) had the greatest activity; Ce/Zr = 74/26 (Rh/CZ-74/26), the least. The Rh/CZ-50/56 also showed specifically high intrinsic activity expressed in terms of turnover frequency (TOF). Different characterization techniques revealed that the Rh and CeO2-ZrO2 support interaction varied according to Ce/Zr composition, and high TOF on Rh/CZ-50/50 was accounted for by the strong Rh and CeO2-ZrO2 support interaction. Although the Rh/CZ-74/26 catalyst was the least active, it was able to catalyze NO reduction with C3H6 when O-2 was eliminated from the reaction gas. In situ FT-IR spectroscopy suggested that formate species formed and stabilized on the Rh/CZ-74/26 catalyst poison the catalytically active sites for NO reduction with C3H6. (C) 2008 Elsevier Inc. All rights reserved.