Evaluating the size of Fe nanoparticles for ammonia adsorption and dehydrogenation

The interaction of NH3 with different Fe clusters and nanoparticles was evaluated using a periodic density functional theory method. The preferred adsorption sites, adsorption energies of NH3, the transition states and the corresponding activation energies of the first NH3 dehydrogenation reaction on different small Fe nanoparticles were compared with those obtained for bare Fe(111) and Fe(111) with an adatom. On seven clusters investigated (Fe16, Fe22, Fe32, Fe59, Fe80, Fe113 and Fe190), NH3 was found to adsorb on top sites, while the NH2 and H products adsorb on bridge and hollow sites, respectively. Higher NH3 adsorption energies were obtained and the dehydrogenation reaction was found to be more exothermic when the size of clusters increases. Although similar activation barriers were found for different nanoparticles and bare surfaces, the NH3 first dehydrogenation is favored when the size of nanoclusters increases.