A DFT Study of the Ammonia Decomposition Mechanism on the Electronically Modified Fe3N Surface by Doping Molybdenum

Ammonia is a potential carbon-free carrier for the on-sitedeliveryof hydrogen and is critical in the development of a hydrogen economy.Designing a noble metal-free catalyst for the low-temperature decompositionof NH3 is a challenging task in this route. We conductedfirst-principles studies to have a comprehensive understanding ofthe ammonia decomposition mechanism on the molybdenum-doped iron nitride(Fe3N) surface. The results indicate that when Mo is dopedon the surface of Fe3N(111) it donates electrons to thesurface and alters the overall electronic structure of the catalyst.The activation energy for the intermediate steps of ammonia decompositionis substantially reduced on the Mo-doped Fe3N surface compared to undoped Fe3N. NH3 adsorbs preferablyon Mo sites over Mo-doped Fe3N(111). However, subsequentintermediate species NH2 and NH prefer Fe sites for adsorption.The activation barrier for the recombination and desorption of nitrogenadatoms is highest compared to the other elementary steps in thebreakdown of NH3 on Mo-doped Fe3N(111) and thereforelimits the overall rate of the decomposition reaction of ammonia.The Bader charge, density of state (DOS), and crystal orbital Hamiltonianpopulation (COHP) calculations elucidate the electronic propertiesof the catalyst.

Automated summary

Ammonia, as a carbon-free carrier for hydrogen, plays a critical role in the development of a hydrogen economy. This study investigates the mechanism of ammonia decomposition on the molybdenum-doped iron nitride surface using first-principles calculations. The results show that the introduction of Mo alters the electronic structure of the catalyst and significantly reduces the activation energy for ammonia decomposition. NH3 preferentially adsorbs on Mo sites, while intermediate species NH2 and NH prefer Fe sites for adsorption.