Theoretical exploration of bare and oxygen-functionalized Ti3C2 clusters for catalytic NH3 production

In this work, we performed high-level quantum chemical calculations to understand the comparative efficiency of Ti₃C₂ and oxygen-functionalized Ti₃C₂ (Ti₃C₂O₂) clusters for the catalytic conversion of N₂ to NH₃. The global minima structures of N₂-free and N₂-adsorbed cluster were predicted using the ABC algorithm. Accordingly, N₂ can be adsorbed on Ti atoms in a side-on fashion. Binding energy, Wiberg bond index, and Bader charge analyses suggest that the N₂-binding ability of the Ti₃C₂O₂ cluster is far better than that of the Ti₃C₂ cluster. Relative free energy diagrams indicate that cluster-catalyzed NH₃ synthesis prefers to follow the distal pathway. The calculation of the energetic span model concludes that catalytic conversion of N₂ to NH₃ on Ti₃C₂O₂ possesses a lower effective activation barrier than that on the Ti₃C₂ cluster, which implies that the Ti₃C₂O₂ is a more efficient catalyst than Ti₃C₂ for the synthesis of NH₃. Moreover, from the comparison with other metal clusters like V₃C₂O₂ and Nb₃C₂O₂, we find that although the latter cluster possesses comparatively less energy span N₂-philicity of Ti₃C₂O₂ is found to be far higher than that of Nb₃C₂O₂ cluster. Thus, the present study will provide a molecular-level understanding of improved N₂ reduction efficiency of the Ti₃C₂ cluster through O-functionalization.

Graphical Abstract

Herein, we have performed quantum chemical calculations to understand the comparative efficiency of Ti₃C₂ and oxygen-functionalized Ti₃C₂ (Ti₃C₂O₂) clusters for the catalytic conversion of N₂ to NH₃. We found that oxygen functionalization can dramatically enhance the N₂ reduction efficiency of the Ti₃C₂ cluster.