Computational Investigation on Adsorption and Dissociation of the NH3 Molecule on the Fe(111) Surface

Our calculations with spin-polarized density functional theory were carried out to characterize the adsorption and dissociation of the NH3 molecule on the Fe(111) surface. The molecular structures and adsorbate/substrate interaction energies of NH3/Fe(111), NH2/Fe(111), NH/Fe(111), N/Fe(111), and H/Fe(111) configurations were predicted. In these calculations, four adsorption sites, such as top (T), bridge (B), 3-fold-shallow (S), and 3-fold-deep (D) sites, of the Fe(111) surface, were considered. It was shown that the barriers for the stepwise NH3 dissociation reaction, NH3(g) -> N-(a) + 3H((a)), are 28.32 kcal/mol (for H2N-H bond activation), 28.49 kcal/mol (for HN-H bond activation), and 25.34 kcal/mol (for N-H bond activation), and the entire process is 20.08 kcal/mol exothermic. To gain insight into the catalytic activity of the Fe(111) surface for the dehydrogenation of NH3, the interaction nature between adsorbate and substrate is also analyzed by the detailed electronic analysis.