The Co/NbN interphase as an effective ammonia synthesis catalyst

Abstract

A spin-mediated promotion mechanism was recently proposed to explain how relatively inert magnetic metals can be activated for ammonia synthesis by introducing metal promoters to quench the surface spin. We herein systematically screen promising promoters and found that many metal promotors are adsorbed at step sites of Co or Ni under ammonia synthesis conditions and act to enhance the activity. We further discuss what can happen for promoters where adsorption on the metal surface is unfavorable. Particularly, metallic Nb would be a good promotor for Co, and we experimentally and theoretically show that it will phase separate and transform into NbN during the reaction, but NbN can still act as a spin promotor at the interface between NbN and Co, leading to a high activity. This work supports the spin effect beyond metal promoters, which could offer more possibilities for utilizing spin effect for designing a wider variety of active catalysts.