Effects of Catalyst Model and High Adsorbate Coverages in ab Initio Studies of Alkane Hydrogenolysis

Abstract

Bare, low-index periodic surface models are typically used to examine metal-catalyzed reactions in density functional theory (DFT) studies, and these most closely resemble low-pressure surface science reactions and catalyzed reactions that occur on large terraces that prevail on large (>5 nm) supported nanoparticles. Many catalytic reactions, however, occur near conditions at which catalytic surfaces are saturated by one or more adsorbed intermediates, leading to strong coadsorbate interactions and surface reconstruction leading to increased curvature. Alkane hydrogenolysis is such a reaction and has been extensively studied using DFT—often on bare metal surfaces—with the assumption that omitted coadsorbed hydrogen atoms (H*) do not significantly alter the relative activation barriers and with ad hoc assumptions about the site requirements for relevant reactions. Here, we use ethane hydrogenolysis on H*-covered Ir catalysts (using a periodic surface model and a nanoparticle model) as a probe reaction to e...