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

Abstract

Ammonia is a potential carbon-free carrier for the on-site delivery of hydrogen and is critical in the development of a hydrogen economy. Designing a noble metal-free catalyst for the lowtemperature decomposition of NH 3 is a challenging task in this route. We conducted first-principles studies to have a comprehensive understanding of the ammonia decomposition mechanism on the molybdenum-doped iron nitride (Fe 3 N) surface. The results indicate that when Mo is doped on the surface of Fe 3 N(111) it donates electrons to the surface and alters the overall electronic structure of the catalyst. The activation energy for the intermediate steps of ammonia decomposition is substantially reduced on the Mo-doped Fe 3 N surface compared to undoped Fe 3 N. NH 3 adsorbs preferably on Mo sites over Mo-doped Fe 3 N(111). However, subsequent intermediate species NH 2 and NH prefer Fe sites for adsorption. The activation barrier for the recombination and desorption of nitrogen adatoms is highest compared to the other elementary steps in the breakdown of NH 3 on Mo-doped Fe 3 N(111) and therefore limits the overall rate of the decomposition reaction of ammonia. The Bader charge, density of state (DOS), and crystal orbital Hamiltonian population (COHP) calculations elucidate the electronic properties of the catalyst.