Supported metals, small particles coprecipitation

A Ni/Si02 catalyst prepared by incipient wetness was shown to consist, initially, of the silica support filled with the nickel salt. On reduction the nickel particles coalesced to form large crystallites because of their weak interaction with the support. Coprecipitated catalysts, however, were composed of layered silicate structures that were more difficult to reduce to metallic nickel. When reduction did take place, though, the reduced crystallites were fixed within the confines of the support so small metal particles with a narrow size range were produced. ... 

The success of Haruta s early work lay in his choice of preparation method and support. Gold particles of the necessary small size were first obtained by coprecipitation (COPPT) and later by deposition-precipitation (DP) (see Sections 4.2.2 and 4.2.3) classical impregnation with HAuCLj does not work. The choice of support is also critical transition metal oxides such as ferric oxide and titania work well, whereas the more commonly used supports, such as silica and alumina, do not work well or only less efficiently. This strongly suggests that the support is in some manner involved in the reaction. 

Coprecipitation gives a solid catalyst containing small metal particles imbedded throughout a porous oxide support. However, not only is this an inefficient use of the metal, it is eilso difficult to produce a support having a prescribed surface area... 

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