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 mi croscope. 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. Spectroscopi c measurements reveal that Ni adatoms create favorable electronic structure s for binding nucleophilic reactants. In addition to this, our observations suggest two new roles for the Ni promoter atoms: (1) increasing the sticki ng probability of sulfur-containing hydrocarbons by binding them to the unr eactive basal planes of MoS2 and (2) transporting these hydrocarbons as ino rganic complexes to the active sites for reaction.