In chemistry, a catalyst support is the material, usually a solid with a high surface area, to which a catalyst is affixed. The reactivity of heterogeneous catalysts and nanomaterial-based catalysts occurs at the surface atoms. Consequently great effort is made to maximize the surface area of a catalyst by distributing it over the support. The support may be inert or participate in the catalytic reactions. Typical supports include various kinds of carbon, alumina, and silica.
Applying catalysts to supports
Two main methods are used to prepare supported catalysts. In the impregnation method, a suspension of the solid support is treated with a solution of a precatalyst, and the resulting material is then activated under conditions that will convert the precatalyst (often a metal salt) to a more active state, perhaps the metal itself. In such cases, the catalyst support is usually in the form of pellets. Alternatively, supported catalysts can be prepared from homogeneous solution by co-precipitation. For example, an acidic solution of aluminium salts and precatalyst are treated with base to precipitate the mixed hydroxide, which is subsequently calcined.
Activation of precatalysts
Supports are usually thermally very stable and withstand processes required to activate precatalysts. For example, many precatalysts are activated by exposure to a stream of hydrogen at high temperatures. Similarly, catalysts become fouled after extended use, and in such cases they are sometimes re-activated by oxidation-reduction cycles, again at high temperatures.
Almost all major catalysts are supported. Largest scale classes of catalysts are Mo-Co-S materials supported on alumina, used for hydrodesulfurization. In the area of organic synthesis, palladium on charcoal is a common hydrogenation catalyst. In Ziegler-Natta olefin polymerization, titanium chloride catalysts are supported on magnesium chloride.
- Zhen Ma, Francisco Zaera "Heterogeneous Catalysis by Metals" in Encyclopedia of Inorganic Chemistry, 2006, John Wiley. doi:10.1002/0470862106.ia084
- L. Keith Hudson, Chanakya Misra, Anthony J. Perrotta, Karl Wefers, F. S. Williams “Aluminum Oxide” in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a01_557.