Direct decomposition of nitrous oxide (N2O) on various metal oxide catalysts was examined in the presence of oxygen. The NiO and Co3O4 catalysts showed high activities. Whereas the activity of the NiO catalyst was only slightly affected by the preparation conditions, the activity of the Co3O4 catalyst severely depended on the preparation conditions. It was found that the sodium content remaining in the precursor was the determining factor for the catalyst activity. Therefore, the effects of alkali doping on the performance of the Co3O4 catalysts were examined by using the catalysts prepared by impregnation of commercial CoCO3 with alkali nitrates and subsequent calcination at 400 degrees C for 4 It. The alkali-doped Co3O4 catalysts showed higher activities than pure Co3O4. Strontium, calcium and barium ions had also favorable effects, but alkaline earth metals required higher concentration to exert the effects than that required by alkali metals. (c) 2006 Elsevier B.V. All rights reserved.