Mechanisms Involving Gold Particles Only

A CO oxidation mechanism involving gold particles only is proposed especially when the support is non-reducible. For instance, Schubert et al. [54] deduced from experiments of CO-O2 time resolved titration and of isotopic exchange, that when gold is supported on magnesia, silica or alumina, the O2 adsorption takes place on low coordinated sites of the gold surface, but leads to a lower activity than when oxygen can be activated on a reducible support. 

We may distinguish four main types of mechanism (1) the reaction proceeds only on metallic gold particle, (2) it requires the simultaneous availability of metallic gold and cationic gold species, (3) it involves collaboration between metal and support, with the possible assistance of cationic species and (4) it proceeds solely via cationic species on the support. In the next section we examine mechanisms 1 and 2 then in Section 6.6.3, we look at mechanisms 3 and 4. 

It does not follow that the mechanism described by the theory is the only mechanism involved in the behaviour of carbon black filler in rubber the geometric or hydrodynamic effect resulting from the Guth-Gold factor properly applied and the particle size continue to play their important part occluded rub-... 

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