Composition, Structure and Texture of Catalysts

3 Composition, structure and texture of catalysts 1.3.1 General terms 

Catalysts may be one-phase or multiphase. In the first case, they may be composed of one substance (for example, alumina or platinum black) or they may be a one-phase solution of two or more substances. In this case, the components of the solution should be given and joined by a hyphen (for example, silica-alumina). 

Support. In multiphase catalysts, the active catalytic material is often present as the minor component dispersed upon a support sometimes called a carrier. The support may be catalyticaliy inert but it may contribute to the overall catalytic activity. Certain bifunctional catalysts ( 1.2.8) constitute an extreme example of this. In naming such a catalyst, the active component should be listed first, the support second and the two words or phrases should be separated by a solidus, for example, platinum/silica or platinum/silica-alumina. The solidus is sometimes replaced by the word on, for example, platinum on alumina. 

Promoter. In some cases, a relatively small quantity of one or more substances, the promoter or promoters, when added to a catalyst improves the activity, the selectivity, or the useful lifetime of the catalyst. In general, a promoter may either augment a desired reaction or suppress an undesired one. There is no formal system of nomenclature for designating promoted catalysts. One may, however, for example, employ the phase iron promoted with alumina and potassium oxide.  

A promoter which works by reducing the tendency for sintering and loss of area may be called a textural promoter (see 1.7.3). 

---