Reaction mechanism of NO decomposition over alkali metal-doped cobalt oxide catalysts

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 O2 caused a decrease in the N2 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 14NO and 15NO 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 N2.