Oxidation State of Gold in Active Catalysts

The positions adopted by investigators are often based on experience with only one system, although they may be claimed to have general relevance it seems more realistic to seek an answer for each individual system. A further problem is that it is not sufficient to state that a given procedure of activation makes an active catalyst it is necessary to know how active it is, and how its activity compares with that found after use of other procedures of activation. Without such information we cannot fully understand the factors that contribute to activity, or to find the conditions for obtaining the best catalytic properties. 

These positions fall into one of four categories. 

From the suggestions found in the literature as summarised in Section 6.3.3, one might conclude that with ceramic oxides, including titania and zirconia, the dominant active species is Au°, either alone or with some cationic species. With ferric oxide, it may be Au° associated with Au111, with magnesia, it may be Au° associated with Au1, and with ceria, it is not clear which combination of the three species is active. 

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