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In chemistry, a catalyst (Greek: καταλύτης, catalytēs) is a substance that decreases the activation energy of a chemical reaction (see also catalysis) without itself being changed at the end of the chemical reaction. Catalysts participate in reactions but are neither reactants nor products of the reaction they catalyse (a strange 'exception' is the process of autocatalysis). More generally, one may at times call anything that accelerates a reaction, without itself being consumed or changed, a "catalyst" (for example, a "catalyst for political change").

A promoter is an accelerator of catalysis, but not a catalyst by itself.

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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 reaction scheme, where C represents the catalyst, A and B are reactants, D is the product of the reaction of A and B:

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Catalyst - Includes archive of past segments, previews of forthcoming episodes, and guidelines for producers.
Meta Description: [ Catalyst is a program that sees science as a dynamic force changing our world. Each week Catalyst will bring a mixture of Australian and international stories, from science breakthroughs investigating the implications, the ethics, and the politics of the particular issue, to stories about how sci... ]

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A music video featuring Lee and Kara from Battlestar Galactica, set to "Catalyst" by Anna Nalick. The video clips belong ...
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