This paper deals with the kinetics of the reduction of nitric oxides by CO, which is a major reaction involved in automotive exhaust three-way catalysts. Spectroscopic and steady state kinetic measurements have been compared in order to explain the different selectivity behavior of Pt- and Rh-based catalysts. particularly during the cold start. It was found that in situ spectroscopy can be a useful tool either for stating on the nature of intermediates or checking the validity of a rate equation. Regarding the kinetics, subsequent calculations and comparisons of thermodynamic and kinetic parameters provide relevant information for modeling purposes. Also, it was found that our kinetic results can be correlated to surface modifications in the particular case of supported bimetallic Pt-Rh catalysts. (C) 2004 Elsevier B.V. All rights reserved.