REACTION-MECHANISM OF NO REDUCTION BY CH4 OVER RARE-EARTH-OXIDES IN OXIDIZING ATMOSPHERE

Rare earth oxides have been examined as catalysts for the catalytic re duction of NO by CH4 in the presence of oxygen. Among the rare earth o xides examined, Sc2O3 and Sm2O3 were found to be active for this react ion. For the Sm2O3 catalyst, ZrO2 was the most effective support. The mechanism of the reaction was studied over the Sm2O3/ZrO2. Kinetic stu dies indicated that CH4 oxidation is initiated by O-2, and NO can reac t only with CH3 radicals formed from the reaction of CH4 with O-2. Ab- initio MO calculations also suggested that CH3 radical is a more favor able reducing species or selective reduction of NO than CH4. It is thu s proposed that NO is reduced into N-2 by the CH3 radical formed from the activation of methane by oxygen.