Hydrodesulphurization Catalysts based on Mo or

Hydrodesulphurization Catalysts Based on Mo or W. - In this Section structural studies of Mo- and W-containing catalysts (unsupported and supported, without and with promoters) and relations between catalyst composition and structure and catalytic properties are reported. Work on sulphides of other metals and on the kinetics and mechanism of hds is reported in the following two Sections. 

Katzer, and G. C. A. Schuit, Chemistry of Catalytic Processes , McGraw-Hill, 1979, Chap. 5. 

Delmon, in Proceedings Climax Third International Conference on the Chemistry and Uses of Molybdenum , ed. H. F. Barry and P. C. H. Mitchell, Climax Molybdenum Co., Ann Arbor, 1980, p. 73. 

It is now generally accepted that in hds catalysts MoSj (or WSj) is the active component and that Co (or Ni) is a promoter that increases the number but does not change the nature of the active sites. However, Massoth points out that, although bulk Co-Mo sulphides are active in hds it is not conclusively proved that bulk sulphides are the active ingredients for hydrodesulphurization reactions for the mildly sulphided catalysts employed in industry . In certain industrial applications representing more severe sulphiding conditions, some bulk sulphides may be present but it is not certain that aU the Mo has been converted to sulphide. 

Although catalysts have been examined by an impressive array of powerful (and expensive) structural techniques a note of caution is necessary. The techniques (other than e.s.r.) may not be sufficiently sensitive to provide information about active sites. For example, the expected maximum concentration of edge-intercalated Co in M0S2 crystallites (0.16 wt.%) is too low to be detected by electron probe microanalysis. Mo at 5% could not be detected by XPS although the concentration of active sites might well 

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