N2O decomposition on supported Rh catalysts (Rh/USY, Rh/SiO2, Rh/Al2O3) has been carried out to study the oxygen coverage (θo) dependence on the activity and to study the mechanism of O2 desorption using an isotopic tracer technique. The decomposition activity for all the Rh catalysts went down to the minimum (formation of only N2), but increased with increasing the coverage, and finally a high activity with steady-state O2 production was attained at high θo. In the isotope study, N216O was pulsed onto 18O/oxidized Rh catalyst at a low temperature (220oC), and desorbed O2 molecules were monitored by means of mass spectrometry. The 18O fraction in the desorbed oxygen had almost the same value as that on the surface oxygen. The result shows that the O2 desorption does not proceed via the Eley-Rideal mechanism, but via the Langmuir-Hinshelwood mechanism, i.e., the desorption of dioxygen through the recombination of adsorbed oxygen. On the other hand, O2-TPD measurement in He showed that desorption of oxygen from the Rh catalyst occurred at much higher temperatures (> 500oC). Therefore, it was proposed that reaction-assisted desorption of O2 takes place during N2O decomposition at the low temperature (220oC).
