Adsorption and dissociation of ammonia on small iron clusters

Abstract

The stepwise dehydrogenation of NHx on small iron clusters is investigated from the density functional theory (DFT) calculations. The results indicate that the fewer the H atoms of the NHx (x = 0–3) species, the higher the adsorption energies of NHx on the same Fe cluster are. Also the larger the cluster size, the stronger the adsorption for the same NHx species is. The catalytic activity of small Fe clusters for NH3 dehydrogenation is comparatively studied, and the rate-limiting steps for the reactions are addressed. It is found that the rate-limiting steps for the dehydrogenation of NHx on the Fe and Fe3 are that for the NH decomposition, and those on the Fe2 and Fe4 are that for the NH2 dissociation. The barriers for the rate-limiting steps are 1.06, 1.49, 1.43 and 1.51 eV for the dehydrogenation of NHx on the Fe, Fe2, Fe3 and Fe4 clusters, respectively. The results suggest that the small Fe clusters can be regarded as the potential candidates for NH3 dehydrogenation reactions and can serve as a reference for further investigations on the catalytic activity of small Fe clusters supported by various catalytic materials.