Adsorption and hydrogenation of pyridine and pyrrole on NiMoS: an ab initio density-functional theory study

The adsorption and first-step hydrogenation of pyridine and pyrrole on the Ni-promoted (image) edge of MoS2 are studied with the use of periodic density-functional theory calculations under generalized gradient approximation. This study represents the first systematic theoretical investigation of the energetics and reaction pathways of possible reaction mechanisms (Langmuir–Hinshelwood, Eley–Rideal) for the hydrogenation of pyridine and pyrrole on the NiMoS catalyst edge plane. The most stable configuration for adsorbed pyridine on the Ni-edge surface is with the molecular plane perpendicular to the surface through Nsingle bondNi bonding. Pyrrole preferably interacts with the surface through the bonding of an α-carbon to a nickel site with the molecular plane flat on the surface. For the hydrogenation of pyridine via a Langmuir–Hinshelwood mechanism, the lowest-activation-energy reaction pathway involves hydrogen from adsorbed H2S; for pyrrole the lowest-activation-energy reaction pathway involves hydrogen from the single bondSH groups at the edge of the MoS2 (0001) basal plane. Eley–Rideal reaction pathways involving gas-phase pyridine or pyrrole and surface hydrogen species require very low activation energy, and thus the dissociation of hydrogen on the catalyst surface would be the rate-determining step under these reaction conditions.