Reaction kinetics and catalyst deactivation during the redn. of NO with CO on a 0.5%Pt-3.4%MoO3/a-Al2O3 catalyst were investigated. The reaction shows an ignition/quenching behavior. After ignition, the reaction kinetics (formation of N2 and N2O) obey the bimol. Langmuir-Hinshelwood equations, in accordance with a dissociative mechanism. A slow catalyst deactivation is obsd. under reductive conditions (pCO >> pNO). The proposed mechanism comprises the formation of electron-withdrawing isocyanates on the Pt surface which slow down the Pt-CO bond formation, which is typical for the quenched state. It is pointed out that the isocyanates delay the formation of the quenched state but that the low activity in the quenched state is due to adsorbed CO.