The structure of the cobalt present in carbon-supported Co and Co-Mo sulfide catalysts was studied by means of X-ray
absorption spectroscopy at the Co K-edge and by X-ray photoelectron spectroscopy (XPS). Thiophene hydrodesulfurization
activities were used to measure the catalytic properties of these catalysts. By comparison of the EXAFS and XANES spectra
of the catalysts with those of c09sS and Cos2 model compounds, it was concluded that all Co atoms in a catalyst prepared
with nitrilotriacetic acid as complexing agent were in the 'Co-Mo-S' state, while the Co atoms in a conventionally prepared
catalyst were partly present in a CO$8-like structure and partly in a 'Co-Mo-S' structure. The Co atoms in the To-Mc-S'
state have a distorted 5- to 6-fold sulfur coordination, and on the average, every Co atom is in contact with two Mo atoms
at a distance of 2.80 A. On the basis of these data, the most likely position for the Co atoms is in front of the square sulfur
faces of the MoS6 trigonal prisms along the edges of the MoS, crystallites with two additional sulfur atoms or H2S molecules
attached. The Co atoms in the sulfided Co/C catalyst have Co-S and Co-Co coordinations as in c09sg, although the sulfur
coordination number is higher
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