On the nature of RuS 2 HDS active sites: insight from ab initio theory

Abstract

The adsorption of thiophene over different hydrogenated RuS 2(1 1 1) defect-surface terminations has been studied using ab initio density functional theory. The highest adsorption energy is obtained for thiophene adsorbing with the molecular ring perpendicular to the surface plane (η 1-coordination) on a stoichiometric termination at a hydrogen coverage involving solely protonic SH species at the surface. However, as previously calculated for the (1 0 0) surface, this position does not seem to favor thiophene activation. The presence of surface hydrides (RuH) stabilizes the η 5-coordination through the enhanced hybridization to the thiophene CS and CC π-states respect to the η 1-position. The largest tendency to thiophene activation with respect to the αCS bond breaking is obtained for a η 5-coordination on a reduced termination exposing coordinatively unsaturated Ru-atoms. In this equilibrium geometry, the thiophene-ring is centered over a hydride specie (RuH) over the sulfur vacancy. Participation of hydridic surface species in the activation process is analyzed in terms of the relative position of the density of H-s-states for both types of hydrogens at the surface. The mechanisms governing the activation are discussed based on the change of the thiophene electronic structure over interaction with the model active-surfaces.