# Atomic Pathways of Ammonia-Driven Fe3O4 Reduction Revealed by First-Principles Calculations

## TL;DR

This study uses computer simulations to understand how ammonia can reduce iron ore at the atomic level, offering a sustainable alternative to hydrogen.

## Contribution

The paper reveals the atomic-scale mechanisms of ammonia-driven Fe3O4 reduction, including dehydrogenation pathways and nitrogen incorporation.

## Key findings

- Ammonia adsorbs upright on Fe3O4(001) surface Fe sites, initiating dehydrogenation.
- Hydrogen migration is the rate-determining step for H2O formation and surface oxygen vacancy generation.
- Nitrogen incorporation into the Fe3O4 lattice promotes Fe nitride formation and prevents excessive N accumulation.

## Abstract

The direct reduction of iron ore using hydrogen faces
challenges
associated with hydrogen storage, transport, and on-site handling.
Ammonia (NH3), with its high hydrogen content, established
distribution infrastructure, and economic viability, has emerged as
a promising alternative reductant. Here, we employ density functional
theory calculations to elucidate the atomic-scale mechanisms governing
NH3 adsorption, dehydrogenation, and nitrogen incorporation
on the Fe3O4(001) surface. Our results show
that NH3 preferentially adsorbs upright at the surface
Fe sites, initiating a sequence of dehydrogenation steps. Among the
three dehydrogenation reaction pathways examined, H migration is identified
as the rate-determining step for H2O formation and desorption,
a process that generates surface oxygen vacancies. The resulting NH
and N species strongly bind to the surface through multiple Fe–N
and Fe–NH coordination bonds. Notably, the most favorable configurationNH
binds adjacent to an oxygen vacancyfacilitates further NH
dissociation into N and H. The generated vacancies migrate favorably
into the subsurface, enabling N incorporation into the lattice and
promoting the formation of Fe nitride. Concurrently, N atoms that
do not incorporate recombine to form N2, thereby preventing
excessive N accumulation on the surface. These results provide atomistic
insights into NH3-driven Fe3O4 reduction
and reveal the coupled vacancy dynamics, H mobility, and N incorporation
pathways that underpin NH3-based ironmaking, highlighting
the mechanistic opportunities for optimizing sustainable iron ore
reduction and advancing NH3-enabled catalytic processes.