Mobile promoters on anisotropic catalysts:: Nickel on MoS2

We have imaged the MoS2 basal plane bare and with adsorbed Ni atoms at 298, 77, and 4 K using a low-temperature ultrahigh vacuum scanning tunneling microscope. Ni atoms freely diffuse across the surface even at 77 K, At 4 K, isolated atoms and small clusters of Ni are stable and can be imaged. At 4 K, Ni atoms can be easily manipulated with the microscope tip. Spectroscopic measurements reveal that Ni adatoms create favorable electronic structures for binding nucleophilic reactants. In addition to this, our observations suggest two new roles for the Ni promoter atoms: (1) increasing the sticking probability of sulfur-containing hydrocarbons by binding them to the unreactive basal planes of MoS2 and (2) transporting these hydrocarbons as inorganic complexes to the active sites for reaction.