Iron-cobalt alloys supported on carbon were investigated as ammonia synthesis catalysts. Barium was found to have a promoting effect for Fe with an optimum atomic ratio Ba/Fe of 0.35. At this Ba loading, a local maximum for the NH3 synthesis activity was found at 4 wt% Co by varying the Fe/Co ratio. Samples containing only Co and no Fe, however, yielded by far the most active catalysts (7.0 mumol (NH3) g(-1) s(-1), 673 K, 10 bar). Barium was a very efficient promoter for Co, increasing the NH3 synthesis activity by more than two orders of magnitude compared to the unpromoted Co samples, while it was not as effective for Fe. Power-law kinetic investigation revealed that, compared to the commercial Fe-based NH3 catalyst, the Ba-Co/C samples showed a lower inhibition by NH3 and were more active under ordinary ammonia synthesis conditions. (C) 2003 Elsevier Science (USA). All rights reserved.