Effect of K, Cs and Ba on the kinetics of NH3 synthesis over carbon-based ruthenium catalysts

The kinetics of NH3 synthesis over carbon-based ruthenium catalysts promoted with barium or alkali was studied. Both the ammonia partial pressure dependencies of the reaction rates (T = 400 degrees C, p = 63 bar, H-2 : N-2 = 3:1) and the pressure variations of the activity (T = 370 degrees C, p= 4-63 bar, H-2 : N-2 = 3:1) were found to be different for Ba and for the alkali (K, Cs). Ba-Ru/C proved to be more sensitive to the NH3 content and to the total pressure. The rate of synthesis over the alkali-promoted catalysts is, in turn, much stronger influenced by the ruthenium dispersion. TOFs of NH3 synthesis for the promoted samples at 370 degrees C and 4 bar (Ba 0.085 1/s, Cs 0.05 1/s, K 0.035 1/s) are significantly higher than that for the Ru(0001) basal plane (0.0085 1/s results from the literature data at 370 degrees C, 2 bar). The most active Ru/C samples (Ba or Cs) exceed significantly the fused iron catalyst, especially at high conversions.