The kinetics of NO decomposition were investigated over alkali metal-doped Co3O4 catalysts. For all the alkali metal-doped Co3O4 catalysts tested, the presence of 02 caused a decrease in the N-2 formation rate with reaction orders between -0.26 and -0.40. The reaction orders with respect to NO were between 1.21 and 1.47, which are higher than unity, suggesting that NO decomposition proceeds via a bimolecular reaction. The observation by in situ Fourier transform infrared (FT-IR) spectroscopy confirmed the presence of nitrite (NO2-) species on the surface under NO decomposition conditions. Isotopic transient kinetic analysis performed using (NO)-N-14 and (NO)-N-15 revealed that a surface-adsorbed species, probably NO2-, serves as an intermediate during NO decomposition. We proposed a reaction mechanism in which the reaction is initiated by NO adsorption onto alkali metals to form NO2- species, which migrates to the interface between the alkali metals and Co3O4, the active sites, and then react with the adsorbed NO species to form N-2. (C) 2004 Elsevier B.V. All rights reserved.