Theoretical Study of the Dissociative Adsorption of Methane on Ir(111): The Role of Steps and Surface Distortions at High Temperatures

In this work we revisit the dissociative adsorption of methane on Ir(111) through density functional theory calculations. We focus on the role of surface defects entailing undercoordinated Ir atoms (e.g., steps), and thermally induced distortions of a defect-free terrace. Though both factors provoke a significant activation of the CH3···H bond cleavage, our results indicate that the latter (surface distortions) is more likely responsible for the low activation energy derived from experiments at high-surface-temperature (Ts = 1000 K) and low impact energy molecules (Ei ≲ 0.15 eV). Still, since surface distortions are strongly attenuated when Ts decreases, dissociation on undercordinated Ir atoms could play a more important role for low surface temperatures. Hence, we provide useful information to guide new experiments intended to unravel the origin of the dominant dissociation pathway for low kinetic energy molecules.