A comparison of the reactivity of lattice nitrogen in Co3Mo3N and Ni2Mo3N catalysts

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 H2/N2 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 N2/H2 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 η-6 carbide structure Co3Mo3N and the β-Mn structure Ni2Mo3N has been investigated. In both cases, lattice nitrogen is found to be reactive towards both H2 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 H2, the nickel molybdenum system reacts to form Ni2Mo3N1−x, whereas comparable conditions with Co3Mo3N produce a novel Co6Mo6N phase.

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