Insight into the Dynamic Evolution of Co3Mo3N Bimetallic Nitride Surface during Ammonia Synthesis

Ammonia production via green hydrogen is regarded as a promising energy carrier for the future. Nevertheless, ammonia synthesis is a structure-sensitive reaction, where the dynamic evolution of catalyst surfaces induced by the reaction atmosphere leads to significant differences between the ideal surface and the realistic surface during the reaction process. Identifying the realistic surface is crucial to gaining a deeper understanding of the reaction mechanisms. In this work, we focus on the formation of stable surfaces for the Co3Mo3N catalyst under the reaction atmosphere. Both theoretical and experimental investigations have demonstrated that the Co3Mo3N catalyst can adjust surface states in response to various conditions. Hydrogenated surfaces and subsurface defects are more likely to form under reaction conditions based on ab initio thermodynamics. A clean surface is thermodynamically less stable than a hydrogenated surface under a wide range of reaction and activation conditions, which has also been confirmed by a series of temperature-programmed experiments. The evolution of the surface has a significant impact on the electronic structure and the reaction performance. This insight into the realistic surface is crucial for understanding the reaction mechanisms and designing high-performance nitride catalysts.