Electronic Descriptors for the Adsorption Energies of Sulfur-Containing Molecules on Co/MoS2, Using DFT Calculations

A set of adsorption energies for all the reaction intermediates completely defines the reaction thermodynamics. Hence, it is important to quantitatively predict adsorption energies for a given system. Describing desulfurization catalysis via transition metal sulfides involves numerous combinations of sulfur-containing molecules and active site geometries. For such a system, a correlative model for adsorption energy predictions would be very useful. We have calculated the eta(1) adsorption energies for 12 different sulfur-containing molecules on 5 different Co-MoS2 metal edge structures. These edge structures give rise to 12 different adsorption modes corresponding to different S-coverages, Co-decorations, and H-coverages. We find adsorption energies for any pair of molecules or any pair of adsorption modes are linearly correlated, confirming the applicability of scaling relationships. Natural bond orbital (NBO)-based electronic descriptors for gas phase adsorbate species are sufficient to describe the adsorption energy variation for a set of adsorbate molecules. A linear regression model indicates that occupancy of the lone pair orbitals for electrons on sulfur plays an important role in determining adsorption energy. Our analysis of the occupancy and energy level of the lone pair of electrons reveals the close relation between aromatic delocalization of the lone pair and adsorption energies of the molecule.