Dissociative Chemisorption of Methane on Stepped Ir(332) Surface: Density Functional Theory and Ab Initio Molecular Dynamics Studies

Surface reactions often have strong site preferences, in which undercoordinated atoms on the surface often dominate due to lower reaction barriers. Understanding the dynamical underpinning of such site selectivity is of great importance for a wide array of heterogeneous processes. Here, we focus on the dissociative chemisorption of methane on terrace and step sites of iridium surfaces, using Ir(332) as a template. Density functional theory revealed not only strong site selectivity, but also clear effects of lattice motion on the dissociation. Ab initio molecular dynamics calculations using the optPBE-vdW functional qualitatively reproduced the experimental initial sticking probabilities at relatively high incidence energies. In this energy range, the reactions all proceed via the direct mechanism. At low incidence energies, trapping and diffusion become prevalent, which can potentially lead to the precursor-mediated mechanism responsible for the negatively activated sticking probability via strong lattice fluctuations at high surface temperatures.