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

Abstract

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.

Design Principle of Molybdenum-Based Metal Nitrides for Lattice Nitrogen-Mediated Ammonia Production

“…We first analyze the electronic effect of coordinated Mo on the lattice N activity. The oxidation state of Mo favors the activation of lattice N, which has been reported in our previous work . Therefore, the charge transfer of Mo exhibits a good linear relationship with the N vacancy formation energy (Figure S17).…”

“…The oxidation state of Mo favors the activation of lattice N, which has been reported in our previous work. 45 Therefore, the charge transfer of Mo exhibits a good linear relationship with the N vacancy formation energy (Figure S17). Interestingly, the magnetization of magnetic metals also exhibits a linear dependence on the N vacancy formation energy (Figure S17).…”

“…In this study, we propose a multistage design strategy to establish the connection between catalyst intrinsic activity and microscopic electronic structure fingerprints using DFT computational energetics as bridges (Figure ). Molybdenum-based metal nitride catalysts (i.e., Co 3 Mo 3 N, Fe 3 Mo 3 N, Ni 3 Mo 3 N, and Mo 2 N), a class of nitride materials with well-defined structures modified by magnetic metals, are employed as model catalysts for lattice nitrogen-mediated ammonia production to decouple the effects of electronic properties and geometrical features. − A combination of DFT calculations, electronic structure analysis, and microkinetic modeling (MKM) has been performed to identify the reaction mechanisms and feature descriptors by correlating the intrinsic activity with the electronic structure. The electron transfer between Mo and magnetic metals and the spin polarization characteristics of the magnetic metals are regarded as descriptors to uncover the atomic-scale causes of intrinsic activity.…”