The catalytic nature of Mo(CO)6 supported on ¿-Al2O3, KOH-doped ¿-Al2O3, and HY-zeolite was investigated in CO oxidation with N2O in comparison with that of a conventional partially reduced MoO3/¿-Al2O3 catalyst. Kinetic parameters of this reaction were obtained in the range 0 to 100 °C; the rate law r = kP1N2OP0CO was found on all catalysts, and the activation energy was estimated to be 9.1 kcal/mol on the Mo(CO)6-derived catalysts and 7.1 kcal/mol on the partially reduced MoO3/¿-Al2O3 catalyst. Maximum catalytic activities were obtained by activating the Mo(CO)6-derived catalysts at 400 °C. To obtain similar activity on the MoO3/¿-Al2O3 catalyst, it was necessary to reduce at 600 °C. The former catalysts were deactivated on repeating the reaction. On the basis of these results and those of ESR studies through the activation or deactivation process, an active site on the Mo(CO)6-derived catalysts has been proposed. Also, clear IR absorption bands due to chemisorbed CO and N2O species were observed on the HY-zeolite-supported catalysts. A reaction mechanism is proposed from the kinetic and IR spectroscopic results.