Mechanistic Investigation of the Catalytic Decomposition of Ammonia (NH₃) on an Fe(100) Surface: A DFT Study

Catalytic decomposition of ammonia (NH₃) is a promising chemical reaction in energy and environmental applications. Density functional theory (DFT) calculations were performed to clarify the detailed catalytic mechanism of NH₃ decomposition on an Fe(100) surface. Specifically, the elementary steps of the mechanism were calculated for the general dehydrogenation pathway of NH₃. The adsorption of two types of ammonia dimers (2NH₃), locally adsorbed NH₃ and hydrogen-bonded NH₃, were then compared, revealing that locally adsorbed NH₃ is more stable than hydrogen-bonded NH₃. By contrast, the dehydrogenation of dimeric NH₃ results in a high energy barrier. Moreover, the catalytic characteristics of NH₃ decomposition on a nitrogen (N)-covered Fe surface must be considered because the recombination of nitrogen (N₂) and desorption have an extremely high energy barrier. Our results indicate that the catalytic characteristics of the NH₃ decomposition reaction are altered by N coverage of the Fe surface. This study primarily focused on energetic and electronic analysis. Finally, we conclude that Fe is an alternative catalyst for the decomposition of NH₃ in CO_x-free hydrogen production.