Abstract
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 Co 3Mo 3N phase in the former case and a mixed phase, containing some Co 3Mo 3N, in the latter. Both ammonolysis and N 2/H 2 pretreatment of nickel molybdate lead to a mixture of Ni 2Mo 3N and Ni, with the latter pretreatment leading to catalysts of higher activity. The reactivity of lattice nitrogen in η-6 carbide structure Co 3Mo 3N and the β-Mn structure Ni 2Mo 3N has been investigated. In both cases, lattice nitrogen is found to be reactive towards both H 2 and C 6H 6 and comparisons demonstrate Co 3Mo 3N to be the more reactive. For Co 3Mo 3N, reaction with benzene yields Co 3Mo 3C and graphite whereas a carbonitride and graphite is produced with Ni 2Mo 3N. In the case of reaction with H 2, the nickel molybdenum system reacts to form Ni 2Mo 3N 1− x , whereas comparable conditions with Co 3Mo 3N produce a novel Co 6Mo 6N phase.
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