NH3 adsorption and dissociation on a nanosized iron cluster

We employed spin-polarized density functional theory to study the bonding and dissociation of NH3 and its fragment on a nanosized icosahedral Fe55 cluster. The site-preference investigations, suggest that for NH3, only the interaction perpendicular to the cluster is favorable (−0.37 eV < B.E.(NH3) < +0.05 eV). Stable geometries of N and H on the high symmetry adsorption site of Fe55 have been calculated as well. Both of these atoms have similar behavior: only the hollow or top sites are stable. Possible dissociation paths of the NH3 to atomic nitrogen and hydrogen were identified. The calculated lowest reaction barrier for the overall process is 1.48 eV. The rate limiting step is the first hydrogen removal from the NH3. Our results suggest that the catalytic activity of iron surfaces towards ammonia-like molecules is enhanched when the metal is in the nanostructured phase.