Mechanistic insight into the hydrazine decomposition on Rh(111): effect of reaction intermediate on catalytic activity

Abstract

Periodic density functional theory (DFT) calculations have been performed to systematically investigate the effect of reaction intermediate on catalytic activity for hydrazine (N₂H₄) decomposition on Rh(111). Reaction mechanisms via intramolecular and NH₂-assisted N₂H₄ decompositions are comparatively analyzed, including adsorption configuration, reaction energy and barrier of elementary step, and reaction network. Our results show that the most favorable N₂H₄ decomposition pathway starts with the initial N–N bond scission to the NH₂ intermediate, followed by stepwise H stripping from adsorbed N₂H_x (x = 1–4) species, and finally forms the N₂ and NH₃ products. Comparatively, the stepwise intramolecular dehydrogenation via N₂H₄ → N₂H₃ → N₂H₂ → N₂H → N₂, and N₂H₄ → NH₂ → NH → N with or without NH₂ promotion effect, are unfavorable due to higher energy barriers encountered. Energy barrier analysis, reaction rate constants, and electronic structures are used to identify the crucial competitive route. The promotion effect of the NH₂ intermediate is structurally reflected in the weakening of the N–H bond and strengthening of the N–N bond in N₂H_x in the coadsorption system; it results intrinsically from the less structural deformation of the adsorbate, and weakening of the interaction between dehydrogenated fragment and departing H in transition state. Our results highlight the crucial effect of reaction intermediate on catalytic activity and provide a theoretical approach to analyze the effect.