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 catalysis in ammonia synthesis. The activity of barium promoted Ru catalysts supported on this treated A.C. is affected remarkably by the Ru precursor. Ru₃(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 Ru₃(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 Ru₃(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.