Pulsed N2O decomposition on an O-18 treated Rh/USY catalyst has been carried out to study the mechanism of O-2 desorption using isotopic tracer technique. The results show that O-2 desorption proceeds at 220degreesC via the Langmuir-Hinshelwood (LH) mechanism, although O-2-TPD measurement showed that desorption of oxygen in He gas from Rh catalyst occurred at much higher temperatures. Therefore, it was proposed that reaction-assisted desorption of O-2 occurs during N2O decomposition. Reaction between N2O and CH4 over an Fe-BEA catalyst was also studied. In the pulse studies, N2O readily reacted with CH4 in the exposure of N2O + CH4 mixture above 200degreesC. In the O-2-TPD studies, a new O-2 desorption peak appeared at the lower temperatures (300-600degreesC) after N2O treatment. However, CH4 was not reactive with the new O(a) species even at 300degreesC. In the FT-IR studies, the peak of Fe-OH was not changed in the exposure of CH4 only, but decreased in the exposure of N2O + CH4 mixture, accompanied with the formation of methoxy and formate species. A possible mechanism is discussed in terms of nascent oxygen transients (O*(a)), which may play an important role in the activation/oxidation of CH4 at initial steps. (C) 2004 Elsevier B.V. All rights reserved.