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

The progressive sulphidation of molybdenum-based hydrotreating model cataly sts is studied using HRTEM and XPS. The catalysts are sulphided quasi in si tu and prepared for TEM measurements in a glovebox. Subsequently, a special ly developed vacuum-transfer specimen holder is used for transfer to the TE M. Using this procedure, a previously unknown feature is observed in the ca talysts. Apart from the well-known slab-like structure of bulk molybdenum d isulphide, manometer-sized spherical entities of molybdenum sulphide or oxy sulphide are observed. For a series of model CoMo/silica catalysts, these " spots" predominantly occur after mild sulphidation procedures. At higher su lphidation temperatures, these spots exist next to the slabs of MOS2-like m aterial. Comparison with practical molybdenum-based hydrotreating catalysts shows that these, too, can contain spots next to or instead of slabs, depe nding on precursor preparation and sulphidation procedures.