Orientation of MoS2Clusters Supported on Two Kinds of γ-Al2O3Single Crystal Surfaces with Different Indices

The effect of surface orientations of supports on microstructures of MoS2clusters was investigated by high-resolution electron microscopy observations of Mo model catalysts supported on γ-Al2O3single crystal thin films with two kinds of surface orientations. By use of an electron beam evaporation method, epitaxial γ-Al2O3single crystal thin films with smooth surfaces were successfully grown on (111) and (100) MgAl2O4substrates. Mo model catalysts were prepared on these γ-Al2O3thin films by the vacuum evaporation method, using MoO3as a source material. After sulfidation at 773 K, relatively uniform basal bonded clusters were grown on (111) γ-Al2O3thin films. The particle size distribution was relatively narrow because of some cluster–support interaction. Their mean particle size was approximately 1.73 nm. On the other hand, edge bonded clusters were grown on (100) γ-Al2O3thin films. The mean cluster length was approximately 2 nm. From further discussions on the cluster–support interface at an atomic level, it seems reasonable to conclude that important factors for determining the orientation of MoS2clusters on γ-Al2O3supports could include similarities between the arrangement of Mo atoms in MoS2and the arrangement of Al or O atoms in γ-Al2O3surface.