A Study of ¹⁵N/¹⁴N Isotopic Exchange over Cobalt Molybdenum Nitrides

Abstract

The ¹⁴N/¹⁵N isotopic exchange pathways over Co₃Mo₃N, a material of interest as an ammonia synthesis catalyst and for the development of nitrogen transfer reactions, have been investigated. Both the homomolecular and heterolytic exchange processes have been studied, and it has been shown that lattice nitrogen species are exchangeable. The exchange behavior was found to be a strong function of pretreatment with ca. 25% of lattice N atoms being exchanged after 40 min at 600 °C after N₂ pretreatment at 700 °C compared to only 6% following similar Ar pretreatment. This observation, for which the potential contribution of adsorbed N species can be discounted, is significant in terms of the application of this material. In the case of the Co₆Mo₆N phase, regeneration to Co₃Mo₃N under ¹⁵N₂ at 600 °C occurs concurrently with ¹⁴N¹⁵N formation. These observations demonstrate the reactivity of nitrogen in the Co-Mo-N system to be a strong function of pretreatment and worthy of further consideration.