Carbon-supported ruthenium catalysts promoted with Ba or Cs were studied in ammonia decomposition. Under the experimental conditions (p = 1 bar, H-2:N-2 = 3:1, 5-50% NH3, 370-400 degreesC), the reaction rates over Cs-Ru/carbon were found to be higher than those over Ba-Ru/carbon, the difference being larger for the high dispersion samples. The effect of the ruthenium precursor (carbonyl, chloride) proved to be unessential for the activity. At 20% NH3 (400 degreesC), TOF of NH3 decomposition over Cs-Ru/carbon was about 3 x 10(2) times higher than for K-Fe/carbon, both based on H-2 chemisorption. The apparent activation energies of 134 and 158 kJ/mol were determined for Cs-Ru/carbon and Ba-Ru/carbon, respectively. The temperature-programmed desorption studies revealed that the amount of nitrogen desorbed from Ba-Ru/carbon was much smaller and the peak position was shifted to higher temperatures when compared to Cs-Ru/carbon. The promoting mechanism of both Ba and Cs is discussed. (C) 2003 Elsevier Inc. All rights reserved.