Revisiting alternative pathways in the Fischer–Tropsch process: Accurate density functional theory calculations on “magic” Ru12 clusters

Abstract

AbstractModels of the Fischer–Tropsch reaction typically focus on two proposed mechanisms for the initial carbon monoxide dissociation: unassisted dissociation (carbide mechanism), and hydrogen‐assisted dissociation via an adsorbed oxymethylidene (HCO*) intermediate. Much evidence for hydrogen‐assisted dissociation comes from density functional theory calculations modeling ruthenium nanoparticle catalysts as infinite, periodic metal slabs. However, the generalized gradient approximations (GGAs) used in these calculations can make significant errors in reaction barrier heights. How these errors affect the predicted selectivity to unassisted vs. hydrogen‐assisted dissociation is not well understood. We address the problem by considering a different regime, applying GGA and beyond‐GGA approximations to CO dissociation on a “magic” nonmagnetic Ru12 cluster modeling supported nanoparticle catalysts. Both approximations concur that hydrogen‐assisted dissociation is facile on this cluster, providing additional support for its potential role in real catalysts.