The direct decomposition of nitric oxide (NO) over barium catalysts supported on various metal oxides was examined in the absence and presence Of O-2. Among the Ba catalysts supported on single-component metal oxides, Ba/CO3O4 and Ba/CeO2 showed high NO decomposition activities, while Ba/Al2O3, Ba/SiO2, and Ba/TiO2 exhibited quite low activities. The effect of an addition of second components to Co and Ce oxides was further examined, and it was found that the activities were significantly enhanced using Ce-Mn mixed oxides as support materials. XRD results indicated the formation of CeO2-MnOx solid solutions with the cubic fluorite structure. O-2-TPD of the CeO2-MnOx solid solutions showed a large desorption peak in a range of relatively low temperature. The BET surface areas of the CeO2-MnOn solid solutions were larger than those of pure CeO2 and Mn2O3. These effects caused by the addition of Mn are responsible for the enhanced activities of the Ba catalysts supported on CeMn mixed oxides. (c) 2006 Elsevier B.V. All rights reserved.