The influence of nitriding conditions upon the ammonia synthesis activities and structures of cobalt molybdenum and nickel molybdenum-based catalysts has been compared. Ammonolysis of cobalt molybdate is observed to produce a more active catalyst than H-2/N-2. pre-treatment. Post-reaction XRD analysis shows a pure Co3Mo3N phase in the former case and a mixed phase, containing some Co3Mo3N, in the latter. Both ammonolysis and N-2/H-2 pretreatment of nickel molybdate lead to a mixture of Ni2Mo3N and Ni, with the latter pretreatment leading to catalysts of higher activity. The reactivity of lattice nitrogen in eta-6 carbide Structure Co3Mo3N and the beta-Mn Structure Ni2Mo3N has been investigated. In both cases, lattice nitrogen is found to be reactive towards both H-2 and C6H6 and comparisons demonstrate Co3Mo3N to be the more reactive. For Co3Mo3N, reaction with benzene yields Co3Mo3C and graphite whereas a carbonitride and graphite is produced with Ni2Mo3N. In the case of reaction with H-2, the nickel molybdenum system reacts to form Ni2Mo3N1-x, whereas comparable conditions with Co3Mo3N produce a novel Co6Mo6N phase. (c) 2008 Elsevier B.V. All rights reserved.