Scanning tunneling microscopy studies of TiO 2-supported hydrotreating catalysts: Anisotropic particle shapes by edge-specific MoS 2–support bonding

Abstract

By means of scanning tunneling microscopy (STM) studies of MoS 2 nanoparticles on a rutile TiO 2(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 MoS 2 nanoparticles on the TiO 2 support. The single-layer MoS 2 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 TiO 2 substrate. Depending on the specific orientation relative to the substrate, the MoS 2 particles exhibit two distinct widths of 33 or 38 Å which originate from the optimized lattice matching distances of the MoS 2 lattice along either of the high symmetry directions of the TiO 2(110) support. Atom-resolved STM images furthermore reveal that the (0001) basal plane of MoS 2 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 MoS 2 nanoparticles to metal oxides by chemical linkages at the particle edges.