Nitrous oxide decomposition studies on an Ru/ZrO2 catalyst (activated by oxidation or reduction at 623 and 773 K) have been performed in a flow reactor at 1 atm total pressure. The reaction onset temperature is 573 K, while a complete conversion of reactant is achieved at 773 K. At a given temperature, the oxidized sample exhibits higher conversions with respect to the reduced one, while an the latter a significant induction period for a stable conversion with time on stream was observed. In situ FTIR experiments have indicated that RuO3 clusters can be found in a dynamic equilibrium with an RuO2 surface layer at the reaction conditions. Ru surface atoms with a valence state greater than 4 end tetrahedrically coordinated were found to be able to interact with N2O at room temperature. At 773 K, upon introduction of N2O a drastic decrease in the N2O vibrational modes is observed with a simultaneous rapid decrease of N2O and increase of O-2 and N-2 in the gas phase. Tt was concluded that during the reaction N2O acts as a reductant of the oxidized ruthenium surface (Ru6+) sites and as an oxidant of RuO2 (Ru4+) sites, (C) 2000 Academic Press.