The observation of nanometer-sized entities in sulphided Mo-based catalysts on various supports

The progressive sulfidation of molybdenum-based hydrotreating model catalysts is studied using HRTEM and XPS. The catalysts are sulfided quasi in situ and prepd. for TEM measurements in a glovebox. Subsequently, a specially developed vacuum-transfer specimen holder is used for transfer to the TEM. Using this procedure, a previously unknown feature is obsd. in the catalysts. Apart from the well-known slab-like structure of bulk molybdenum disulfide, nanometer-sized spherical entities of molybdenum sulfide or oxysulfide are obsd. For a series of model Co-Mo/silica catalysts, these \"spots\" predominantly occur after mild sulfidation procedures. At higher sulfidation temps., these spots exist next to the slabs of MoS2-like material. Comparison with practical molybdenum-based hydrotreating catalysts shows that these, too, can contain spots next to or instead of slabs, depending on precursor prepn. and sulfidation procedures. [on SciFinder (R)]