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Created page with 'File:lighterstill.jpgright|frame '''Catalyst''' (or Catalysis) the process in which the rate of a chemical reaction is either increased ...'
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'''Catalyst''' (or Catalysis) the [[process]] in which the rate of a [[chemical]] [[reaction]] is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that [[participate]] in the chemical reaction, a catalyst is not consumed by the reaction itself. The catalyst may participate in multiple chemical [[transformations]]. Catalysts that speed the reaction are called positive catalysts. Catalysts that slow down the reaction are called negative catalysts or inhibitors. Substances that increase the [[activity]] of catalysts are called promoters and substances that deactivate catalysts are called catalytic [[poison]]s.
The general [[Attribute|feature]] of catalysis is that the catalytic reaction has a lower rate-limiting free [[energy]] [[change]] to the transition [[state]] than the corresponding uncatalyzed reaction, resulting in a larger reaction rate at the same temperature. However, the [[mechanistic]] [[origin]] of catalysis is [[complex]]. Catalysts may affect the reaction environment favorably, e.g. acid catalysts for reactions of carbonyl compounds form specific intermediates that are not produced naturally, such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause lysis of reagents to reactive forms, such as atomic hydrogen in catalytic hydrogenation.
Kinetically, catalytic reactions behave like typical chemical reactions, i.e. the reaction rate depends on the frequency of contact of the reactants in the rate-determining step. Usually, the catalyst participates in this slow step, and rates are limited by amount of catalyst. In heterogeneous catalysis, the diffusion of reagents to the [[surface]] and diffusion of products from the surface can be rate determining. [[Analogous]] [[events]] associated with substrate binding and product dissociation apply to homogeneous catalysts.
Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated or destroyed by secondary [[processes]]. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid-liquid system or evaporate in a solid-gas system.
==History==
In a general sense, anything that increases the rate of a [[process]] is a "catalyst", a term derived from [[Greek]] καταλύειν, meaning "to annul," or "to untie," or "to pick up." The phrase catalysed processes was coined by [http://en.wikipedia.org/wiki/J%C3%B6ns_Jakob_Berzelius Jöns Jakob Berzelius] in 1836 to describe reactions that are accelerated by substances that remain unchanged after the reaction. Other early chemists involved in catalysis were [http://en.wikipedia.org/wiki/Alexander_Mitscherlich Alexander Mitscherlich] who referred to ''contact processes'' and [http://en.wikipedia.org/wiki/Johann_Wolfgang_D%C3%B6bereiner Johann Wolfgang Döbereiner] who spoke of ''contact action'' and whose lighter based on hydrogen and a platinum sponge became a huge commercial success in the 1820s. [http://en.wikipedia.org/wiki/Humphry_Davy Humphry Davy] [[discovered]] the use of platinum in catalysis. In the 1880s, Wilhelm Ostwald at Leipzig University started a systematic investigation into reactions that were catalyzed by the presence of acids and bases, and found that chemical reactions occur at finite rates and that these rates can be used to determine the strengths of acids and bases. For this work, Ostwald was awarded the 1909 [[Nobel Prize]] in Chemistry.
==External links==
* [http://scienceaid.co.uk/chemistry/inorganic/catalysis.html Science Aid: Catalysts] Page for high school level science
* W.A. Herrmann Technische Universität presentation [http://aci.anorg.chemie.tu-muenchen.de/wah/vortraege/catalysis.pdf]
* [http://www.tuat.ac.jp/~kameyama/ Alumite Catalyst, Kameyama-Sakurai Laboratory, Japan]
* [http://www.inorganic-chemistry-and-catalysis.eu/ Inorganic Chemistry and Catalysis Group, Utrecht University, The Netherlands]
* [http://www.biw.kuleuven.be/ifc/cok/home.htm Centre for Surface Chemistry and Catalysis]
* [http://www.udec.cl/~carbocat Carbons & Catalysts Group, University of Concepcion, Chile]
* [http://www.nsfcentc.org Center for Enabling New Technologies Through Catalysis, An NSF Center for Chemical Innovation, USA]
*[http://www.sciencenews.org/view/generic/id/42507/title/Bubbles_turn_on_chemical_catalysts]"Bubbles turn on chemical catalysts," Science News magazine online, April 6, 2009.
[[Category: Chemistry]]
'''Catalyst''' (or Catalysis) the [[process]] in which the rate of a [[chemical]] [[reaction]] is either increased or decreased by means of a chemical substance known as a catalyst. Unlike other reagents that [[participate]] in the chemical reaction, a catalyst is not consumed by the reaction itself. The catalyst may participate in multiple chemical [[transformations]]. Catalysts that speed the reaction are called positive catalysts. Catalysts that slow down the reaction are called negative catalysts or inhibitors. Substances that increase the [[activity]] of catalysts are called promoters and substances that deactivate catalysts are called catalytic [[poison]]s.
The general [[Attribute|feature]] of catalysis is that the catalytic reaction has a lower rate-limiting free [[energy]] [[change]] to the transition [[state]] than the corresponding uncatalyzed reaction, resulting in a larger reaction rate at the same temperature. However, the [[mechanistic]] [[origin]] of catalysis is [[complex]]. Catalysts may affect the reaction environment favorably, e.g. acid catalysts for reactions of carbonyl compounds form specific intermediates that are not produced naturally, such as osmate esters in osmium tetroxide-catalyzed dihydroxylation of alkenes, or cause lysis of reagents to reactive forms, such as atomic hydrogen in catalytic hydrogenation.
Kinetically, catalytic reactions behave like typical chemical reactions, i.e. the reaction rate depends on the frequency of contact of the reactants in the rate-determining step. Usually, the catalyst participates in this slow step, and rates are limited by amount of catalyst. In heterogeneous catalysis, the diffusion of reagents to the [[surface]] and diffusion of products from the surface can be rate determining. [[Analogous]] [[events]] associated with substrate binding and product dissociation apply to homogeneous catalysts.
Although catalysts are not consumed by the reaction itself, they may be inhibited, deactivated or destroyed by secondary [[processes]]. In heterogeneous catalysis, typical secondary processes include coking where the catalyst becomes covered by polymeric side products. Additionally, heterogeneous catalysts can dissolve into the solution in a solid-liquid system or evaporate in a solid-gas system.
==History==
In a general sense, anything that increases the rate of a [[process]] is a "catalyst", a term derived from [[Greek]] καταλύειν, meaning "to annul," or "to untie," or "to pick up." The phrase catalysed processes was coined by [http://en.wikipedia.org/wiki/J%C3%B6ns_Jakob_Berzelius Jöns Jakob Berzelius] in 1836 to describe reactions that are accelerated by substances that remain unchanged after the reaction. Other early chemists involved in catalysis were [http://en.wikipedia.org/wiki/Alexander_Mitscherlich Alexander Mitscherlich] who referred to ''contact processes'' and [http://en.wikipedia.org/wiki/Johann_Wolfgang_D%C3%B6bereiner Johann Wolfgang Döbereiner] who spoke of ''contact action'' and whose lighter based on hydrogen and a platinum sponge became a huge commercial success in the 1820s. [http://en.wikipedia.org/wiki/Humphry_Davy Humphry Davy] [[discovered]] the use of platinum in catalysis. In the 1880s, Wilhelm Ostwald at Leipzig University started a systematic investigation into reactions that were catalyzed by the presence of acids and bases, and found that chemical reactions occur at finite rates and that these rates can be used to determine the strengths of acids and bases. For this work, Ostwald was awarded the 1909 [[Nobel Prize]] in Chemistry.
==External links==
* [http://scienceaid.co.uk/chemistry/inorganic/catalysis.html Science Aid: Catalysts] Page for high school level science
* W.A. Herrmann Technische Universität presentation [http://aci.anorg.chemie.tu-muenchen.de/wah/vortraege/catalysis.pdf]
* [http://www.tuat.ac.jp/~kameyama/ Alumite Catalyst, Kameyama-Sakurai Laboratory, Japan]
* [http://www.inorganic-chemistry-and-catalysis.eu/ Inorganic Chemistry and Catalysis Group, Utrecht University, The Netherlands]
* [http://www.biw.kuleuven.be/ifc/cok/home.htm Centre for Surface Chemistry and Catalysis]
* [http://www.udec.cl/~carbocat Carbons & Catalysts Group, University of Concepcion, Chile]
* [http://www.nsfcentc.org Center for Enabling New Technologies Through Catalysis, An NSF Center for Chemical Innovation, USA]
*[http://www.sciencenews.org/view/generic/id/42507/title/Bubbles_turn_on_chemical_catalysts]"Bubbles turn on chemical catalysts," Science News magazine online, April 6, 2009.
[[Category: Chemistry]]