High resolution electron microscopy and microanalysis of carbon-supported hydrodesulfurization catalysts

Experimental carbon-supported hydrodesulfurization (HDS) catalysts have been shown to exhibit oxidic precursors with morphologies of heavy metal species ranging from near-atomic level dispersions to discrete crystalline particles, dependent upon preparative conditions. The effects of sulfiding on these catalysts precursors have been studied by high resolution TEM and EDS microanalysis techniques. A precursor having oxide platelets of uniform composition in the 5-10 nm size range offers promise as a model system for characterization of the structure of active sites after sulfidation, in an attempt to clarify models proposed in the literature. The dedicated scanning transmission electron microscope (STEM) permits EDS micro-analyses of spatial resolution sufficient to determine elemental distributions in such small particles. After a partial sulfidation, the particles exhibit sulfide layering around the residual oxide particle, with Co clearly enriched at the surface.