Assessing the Activity Trend of Metal Nitride Catalysts for Ammonia Synthesis Based on Theory of Chemical Potential Kinetics

Ammonia synthesis is like a never-ending catalytic race over the past century with various efficient catalysts developed. Amongst them, metal nitrides (MNs) have been widely investigated and reported to be active. Here, we propose a simple but efficient approach to assess the activity trend of metal nitride catalysts for ammonia synthesis with density functional calculations. Based on theory of chemical potential kinetics and an extended two-step kinetic model, taking the nitrogen vacancy formation energy and the nitrogen molecular or dissociative adsorption energy as descriptors, we obtain the optimal descriptor window for a good MN catalyst and find CeN, LaN, VN and NbN as promising candidates. These catalysts are reported in previous experimental studies to show excellent performance for the ammonia synthesis reaction. Subsequently, the candidates determined are further verified with free energy profiles obtained for all possible reaction pathways and intermediates, and the stabilities of these catalysts are also discussed.