Dissociative Chemisorption of Hydrazine on an Fe{211} Surface

Abstract

Density functional theory is employed to investigate the stepwise decomposition of hydrazine on Fe{211}. Local energy minima are described for N2Hx (x = 0–4) intermediates, along with the transition states and pathways that connect them. We find that the dehydrogenation (N–H scission) and nitrogen decoupling (N–N scission) steps have activation energies in the range of 0.91 to 1.04 eV, with the exception of bond-breaking in NNH2 (barrier of 0.52 eV) and for NNH (barrier of 0.55 eV). The reverse reactions of hydrogenation (N–H formation) and nitrogen coupling (N–N formation) have activation energies between 1.24 and 2.01 eV and 2.33 and 4.46 eV, respectively. Dehydrogenation and nitrogen decoupling are therefore generally competitive routes for hydrazine decomposition, with the dominant surface products at low-to-moderate temperatures being NH2 moieties and N adatoms. Elevated temperatures should allow for the evolution of gas-phase N2 and NH3, the latter species being particularly favored under conditions of excess hydrogen.