Properties of Nanoparticulate Gold Catalysts

Properties of the supported An nanocatalysts have been found to depend on the method of preparation, and the pretreatment and calcination procedures used [18,31,44,125[. This section discusses the most important properties of catal3dic gold nanoparticles. 

Although, the reasons for the catal3dic activity of gold are not as yet fully understood, the presence of gold as well-dispersed nanoparticles ( 10nm) 

Nevertheless, unsupported powdered gold (mean diameter, 76 nm) proved to be active for CO oxidation [138,139], and so did naked gold [140] and gold nanotubes [141] under mild conditions. In addition, investigations by Flytzani-Stephanopoulos and co-workers [142-144] on the water-gas shift (WGS) reaction (see Sect. 6.4.1) have challenged the idea that gold nanoparticles are essential, but these investigators have not exhaustively proved the complete absence of Au(0). 

The most usual supports are transition metal oxides [7,38,53,54,154,155]. The role of these is still a matter of discussion and two different classes of oxides can be identified [90,152]. The first class comprises active supports. These are materials that can be relatively easily reduced such as NiO, Fc203 or Ti02. The second class is formed by inert, so-called inactive supports such as MgO, AI2O3 and Si02. These supports can, in some cases, lead to catalysts as active as those with reducible supports [32], but it is very important to ensure a high dispersion of very small particles of gold on the oxide [47,90]. 

Alumina is the support most commonly used for PGM industrial catalysts [8,36,47], but not all investigators regard AI2O3 as a good support for gold catalysts. Schubert and co-workers found that AI2O3 was not as effective 

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