Ruthenium catalysts (4.6 wt.%) supported on the magnesium-aluminum spinet and promoted with barium (Ba:Ru = 1: 1 molar ratio) or caesium (Cs:Ru = 1: 1) were studied in the reaction of ammonia decomposition under a I bar pressure. Both Ba-Ru/MgAl2O4 and Cs-Ru/MgAl2O4 proved to be significantly more active than the unpromoted system (a factor of 10) and more active than the conventional magnetite-based catalyst used commonly in the NH3 synthesis. However, the surfaces of the spinet-based catalysts were less active (TOF) than those of analogously promoted (Ba, Cs) ruthenium on carbon. (C) 2003 Elsevier B.V. All rights reserved.