A comparison of the reactivity of lattice nitrogen in Co 3Mo 3N and Ni 2Mo 3N catalysts

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.