Scanning tunneling microscopy studies of TiO₂-supported hydrotreating catalysts: Anisotropic particle shapes by edge-specific MoS₂-support bonding

By means of scanning tunneling microscopy (STM) studies Of MoS₂ nanoparticles on a rutile TiO₂(110) Support, we have studied fundamental atomic-scale aspects of the particle-support interactions for metal-sulfide hydrotreating catalysts on a metal oxide support. The STM results reveal that strong particle-support interactions at the particle edges have an overriding effect on the equilibrium shape of single-layer MoS₂ nanoparticles on the TiO₂ Support. The single-layer MoS₂ nanoparticles are observed to be in flat contact with the metal oxide surface and preferentially adopt the shape of uniform elongated platelets oriented along one of the high-symmetry directions of the two-fold symmetric TiO₂ substrate. Depending on the specific orientation relative to the substrate, the MoS₂ particles exhibit two distinct widths of 33 or 38 angstrom which originate from the optimized lattice matching distances of the MoS₂ lattice along either of the high symmetry directions of the TiO₂(110) support. Atom-resolved STM images furthermore reveal that the (0001) basal plane Of MoS₂ appears unperturbed showing that predominantly strong edge bonding effects control the particle morphology in this catalyst. The experimental STM results thus give strong support to recent edge-bonding models from the literature investigating the adhesion of MoS₂ nanoparticles to metal oxides by chemical linkages at the particle edges.