Catalyst

A catalyst (Greek: καταλύτης, catalyt?s) is a substance that accelerates the rate (speed) of a chemical reaction without itself being transformed or consumed by the reaction (see also catalysis). Chemical catalysts, the focus of this article, participate in reactions but are neither chemical reactants nor chemical products. More generally, one may sometimes call anything which accelerates a reaction without itself being consumed or transformed a catalyst (for example, a "catalyst for political change").

Types of catalysts

Catalysts can be heterogeneous, or homogeneous. Heterogeneous catalysts are present in different phases from the reactants (e.g. a solid catalyst in a liquid reaction mixture), whereas homogenous catalysts are in the same phase (e.g. a dissolved catalyst in a liquid reaction mixture). A simple model for heterogeneous catalysis involves the catalyst providing a surface on which the reactants (or substrates) temporarily become adsorbed. Bonds in the substrate become weakened sufficiently for new products to be created. The bonds between the products and the catalyst are weaker, so the products are released.

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Homogenous catalysts generally react with one or more reactants to form a chemical intermediate that subsequently reacts to form the final reaction product, in the process regenerating the catalyst. The following is a typical catalytic reaction scheme, where C represents the catalyst:

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:A + C → AC (1)

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:B + AC → AB + C (2)

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Although the catalyst (C) is consumed by reaction 1, it is subsequently produced by reaction 2, so for the overall reaction:

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:A + B + C → AB + C

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the catalyst is neither consumed nor produced. Enzymes are biocatalysts.

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Use of "catalyst" in a broader cultural sense is in rough analogy to the sense described here. Other biocatalysts are ribozymes and deoxyribozymes.

Related Topics:
Ribozyme - Deoxyribozyme

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