Influence of reducing and sulfiding treatments on Co/Al/sub 2/O/sub 3/ and Mo/Al/sub 2/O/sub 3/ catalysts. An X-ray photoelectron spectroscopy study

X-ray photoelectron spectroscopy (XPS) has been used to investigate the phase transformations induced by various pretreatments of Co/Al/sub 2/O/sub 3/ and Mo/Al/sub 2/O/sub 3/. Upon sulfiding by H/sub 2/-H/sub 2/S, Co/sup 2+/ is partly reduced to Co/sup 0/ while the Mo/sup 6+/ species is completely transformed into MoS/sub 2/. The behaviour of molybdenum is similar to that observed in Co-Mo/Al/sub 2/O/sub 3/ hydrodesulfurization catalysts. In contrast, cobalt gives Co/sup 0/ in Co/Al/sub 2/O/sub 3/ systems whereas Co/sub 9/S/sub 8 / is observed for HDS catalysts. A nonreducible alumina bound Co is also observed in both the presence and absence of molybdenum. In the oxide form, molybdenum species are in strong interaction with the support but this interaction does not exist after sulfiding.Anglai

Comparative study of unsupported and supported Co-Mo hydrodesulphurisation catalysts

Catalytic activities of unsupported and alumina- or silica-supported cobalt-molybdenum catalysts in the oxidic and sulphided form are compared. Silica-supported catalysts behave essentially as unsupported catalysts. The behaviour of alumina-supported catalysts is quite different. The synergistic effect is much stronger, especially in the sulphided form, and the domain in which the synergism is exhibited is much broader. In addition, alumina brings about a strong hydrogenating activity. ESCA measurements have helped to investigate further the interaction between the cobalt-molybdenum system and alumina.Anglai