Effect of ruthenium precursor on hydrogen-treated active carbon supported ruthenium catalysts for ammonia synthesis

Active carbon (A.C.), after treatment at 1123 K with hydrogen for more than 24 h, was found to be very effective as a support for ruthenium catalysts in ammonia synthesis. The activity of barium promoted Ru catalysts supported on this treated A.C, is affected remarkably by the Ru precursor. Ru-3(CO)(12) was found previously to be the most effective Ru precursor for oxide supports such as Al2O3, MgO, and CeO2 in ammonia synthesis. However, in this study, the Ru-BaO/A.C. catalyst prepared from Ru(acac)(3) was found to yield the highest activity, while the catalyst prepared from Ru-3(CO)(12) resulted in the lowest activity among several precursors. Transmission electron microscopy and hydrogen chemisorption showed that the particle size of Ru obtained from the decomposition of Ru(acac)(3) on hydrogen-treated A.C, is smaller than the particle size of Ru obtained from the decomposition of Ru-3(CO)(12). Additionally, RuCl3 was found to be an effective precursor for Ru/A.C, catalyst. It has been suggested that chlorine ions can be removed easily from A.C. by hydrogen reduction at 773 K, and that this results in the high activity. (C) 1998 Elsevier Science S.A. All rights reserved.