Ammonia decomposition over the carbon-based ruthenium catalyst promoted with barium or cesium

Carbon-supported ruthenium catalysts promoted with Ba or Cs were studied in ammonia decomposition. Under the experimental conditions (p=1 bar, H2:N2=3:1, 5–50% NH3, 370–400 °C), 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 °C), TOF of NH3 decomposition over Cs–Ru/carbon was about 3×102 times higher than for K–Fe/carbon, both based on H2 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.