The effect of cerium and lanthanum oxides in cobalt oxide catalysts for both activity and selectivity in ammonia oxidation was studied. The molar ratios of Ce/Co and La/Co in the catalysts were 0.02. All the catalysts were characterized by XRD. The activity was measured in a fixed bed reactor at a temperature range of 720-820 degrees C. Cerium oxide proved to be a more efficient promoter than lanthanum oxide, both being advantageous. The selectivity of ammonia oxidation to NO over Ce-containing sample was even as high as 97.7% and the selectivity to N2O was as low as 0.5%. (C) 2000 Elsevier Science B.V. All rights reserved.