A Comparison of the Reactivity of the Lattice Nitrogen in Tungsten Substituted Co Mo N and Ni Mo N.

The effect of the partial substitution of Mo with W in Co Mo N and Ni Mo N on ammonia synthesis activity and lattice nitrogen reactivity has been investigated. This is of interest as the coordination environment of lattice N is changed by this process. When tungsten was introduced into the metal nitrides by substitution of Mo atoms, the catalytic performance was observed to have decreased. As expected, Co Mo N was reduced to Co Mo N under a 3 : 1 ratio of H /Ar. Co Mo W N was also shown to lose a large percentage of lattice nitrogen under these conditions. The bulk lattice nitrogen in Ni Mo N and Ni Mo W N was unreactive, demonstrating that substitution with tungsten does not have a significant effect on lattice N reactivity. Computational calculations reveal that the vacancy formation energy for Ni Mo N is more endothermic than Co Mo N. Furthermore, calculations suggest that the inclusion of W does not have a substantial impact on the surface N vacancy formation energy or the N adsorption and activation at the vacancy site.