In:
Bulletin des Sociétés Chimiques Belges, Wiley, Vol. 93, No. 8-9 ( 1984-01), p. 783-806
Abstract:
The present article will discuss the recent developments which have taken place with the “Co‐Mo‐S model”. Some new results will also be presented to elucidate some of the controversies which have existed in the literature. The Co‐Mo‐S model, which was originally based on Mössbauer emission spectroscopy (MES) measurements, has now been confirmed and further developed by use of extended x‐ray absorption fine structure (EXAFS), infrared spectroscopy (ir), x‐ray photoelectron spectroscopy (XPS), high resolution and analytical electron microscopy (HREM and AEM), magnetic susceptibility and other methods. The following are some of the main conclusions: (i) Mo is present mainly as MoS 2 ‐like phases; (ii) in the catalytically active Co‐Mo‐S structures, the promoter atoms are located at the edges of the MoS 2 ‐like structures; (iii) the chemical and catalytic properties of the Co edge atoms are strongly influenced by the MoS 2 “support”; (iv) in typical alumina supported catalysts, the MoS 3 domains appear to be predominantly present as small single sheets which have a large fraction of the Mo atoms present at edge positions (this is an important property since it allows highly active catalysts to be prepared); (v) the presence of Co 9 S 8 , cobalt in the alumina or unpromoted MoS 2 is seen to have little influence on the HDS activity; (vi) in typical Co‐Mo/Al 2 o 3 catalysts strong interactions exist between Co‐Mo‐S and the support probably in the torn of Mo‐S or Mo‐O bridges to the alumina (this influences both the chemical and catalytic properties of Co‐Mo‐S); (vii) the Co‐Mo‐S model can explain the catalytic behavior of unsupported and supported catalysts including carbon supported catalysts; (viii) besides Co‐Mo‐S, evidence for similar Ni‐Mo‐S, Co‐M‐S, Ni‐W‐S and Fe‐Mo‐S structures has been found. The promotional effect depends on the nature of the atoms at the MoS 2 (or WS 2 ) edges and for Fe‐Mo‐S, the effect is slightly negative; (ix) the nature of the active sites has been observed to be different in unpromoted and promoted catalysts; (x) for unpromoted Mo catalysts edge sites have a higher HDS activity than corner sites; (xi) Co‐Mo‐S and Ni‐Mo‐S type structures have also been observed to play a role in hydrogenation.
Type of Medium:
Online Resource
ISSN:
0037-9646
,
0037-9646
DOI:
10.1002/bscb.v93:8/9
DOI:
10.1002/bscb.19840930820
Language:
English
Publisher:
Wiley
Publication Date:
1984
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