State of Molybdena Catalysts

Molybdena catalysts generally need to be activated by reduction or sulfidation in order to obtain an active catalyst for most reactions in which they are employed (except for oxidation-type reactions). Therefore, it is important to determine what changes occur in the state of the oxidized catalyst when it is subjected to these activation pretreatments. 

Another interpretation, based on a molybdena monolayer, invokes differences in the Mo-0 bond strength due to Mo interactions with Al sites of varying strength (23). Reduction then involves removal of the 

Evidence for Mo5+ and vacancies has already been discussed earlier in this article. Fransen et al. (85), have shown that the monolayer is not destroyed by reduction. 

The situation with respect to Co/Al catalysts is less certain. At low levels of Co, no reduction occurs, whereas at higher levels, some reduction occurs. It is likely that reduction in the latter case is due to the ready reducibility of Co304. One may surmise that Co[T] is not reducible in view of the resistance of CoA1204 to reduction. However, whether Co[0] in other forms besides bulk Co304 (or CoO) reduces (if indeed it is present) is not known. 

When Co and Mo co-exist on the oxidized catalyst, total disagreement exists between various investigators on ease of reducibility. Some claim Co enhances Mo reduction, others that it impedes and still others that it has no effect. Here again, catalyst preparation and mode of addition of the Co and Mo could have a bearing on these results. Clearly, more research on this point is needed to get a better picture of the Co-Mo interactions which may be present. 

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