Catalyst

of these articles treats a certain kind of chemical materials, for the emission control of vehicles, sees vehicle catalyst.

The catalyst (of the catalysis, Greek κατάλυσις, katálysis - dissolution with Latin ending) is a material, that the reaction rate of a chemical reactionaffected, without thereby to be used. This takes place by means of up or reduction of the activation energy. Catalysts, which lower the activation energy, are called positive catalysts, such, which raise the activation energy, as negative catalysts or inhibitors. Catalysts change thusto change kinetics of chemical reactions without their thermodynamics. They accelerate and/or. slow down and the backward reaction equally and change thus nothing in the equilibrium of a reaction.

Characteristics of a catalyst:

  • a reaction lies after a reaction
  • invariably forwards accelerated/slows down (those changesReaction rate)
  • increased/reduces the activation energy
  • works selectively (certain reactions need certain catalysts)

further technical terms about catalyst: Catalysis, autocatalysis, homogeneous catalysis, heterogeneous catalysis, catalyst poison and biocatalyst.

Table of contents

history

since the antique one chemical reactions are implemented by catalysts. Only Jöns Jakob Berzelius came 1835 to the realization that a multiplicity ofReactions took place only if a certain material present were, which was not used however. According to its opinion these materials were not converted, supplied however by their presence the energy over their catalytic Kraft. It called these materials catalysts.

In the future it, deeper understanding for the thermodynamic succeeded background to the catalysis to win. William Ostwald defined the catalyst as follows:

“A catalyst is a material, which increases the speed of a chemical reaction, without even thereby used up tooand without the final situation of the thermodynamic equilibrium of this reaction will change. “

For its work around the catalysis William Ostwald received the Nobelpreis for chemistry.

chemistry

the impact of a catalyst is based on its possibility, thatTo change mechanism of a chemical reaction in such a manner that the activation energy is changed. One “goes another way” on the potential hyperlevel (the potential is in general. a function of several variables. Therefore is i.e. in the simplest case, the dependence of the potentialof only two variables, which change, the potential a three-dimensional level. The variables can e.g. two connection distances between the reactants its, which change during the reaction. This simplest case is descriptive, but unrealistic.). This takes place over thoseEducation of a reactive intermediate connection (complex also activated) and the further Abreaktion to the final products, whereby the assigned catalyst is regressed. In practice however catalysts become i. D. R. by secondary reactions after some time of the use ineffectively, there itby by-products to be blocked. The following diagram (Arrhenius - diagram) arises as cut as a result of the energy hyperpotential surface.


Bild:Katreak2.png

In the diagram the upper curve gives the reaction

< math> A + B \ rightarrow STARTING FROM </math>

again. The activation energy becomes with <math> A_U</math> designated. The lower curve shows the energy process through <math> C </math> catalyzed reaction. Here becomes over a transient condition (1. Maximum) a minimum reaches, which the enthalpy of the connection <math> AC </math> corresponds.

<math> A + C \ rightarrow AC</math>

Over a further transient condition the product becomes <math> STARTING FROM </math> reached, whereby the catalyst <math> C </math> one regresses.

<math> B + AC \ rightarrow OFF + C </math>

With <math> A_C </math> designated activation energy of the catalyzed reaction is clearly smaller.

As example the catalytic burn can be stated of hydrogen with oxygen. This burn is thermodynamically so favorably that it should run off in principle “voluntarily”, however due to the activation energy high at room temperature is so strongly restrained that the reaction rateis very small. The presence of a platinum catalyst can degrade this activation energy in such a manner that this reaction runs off then sufficiently fast even at lower temperatures. An application for it was the Döbereiner lighter.

With Gleichgewichtsreaktionen a catalyst changes and backward reaction upthe same way, so that the situation of the equilibrium is not changed, the equilibrium however faster adjusts itself.

seem to meaning

Aufgeschnittener Fahrzeugkatalysator
of the catalysts cut open

vehicle catalyst catalysts in nature in various way. In organisms nearly everything runsvitally necessary chemical reactions catalyzes off (e.g. during photosynthesis, the respiration or the power production from the food). The used catalysts are usually certain proteins, the enzymes.

The reduction of the activation energy by positive catalysts is with chemical reactionsof great (commercial) importance. In more than 80% of all chemical industriellen processes are used catalysts. Without the presence of the catalyst the respective chemical reaction would take place very many more slowly or not at all. Therefore catalysts nowadays hardly still are from thatTo exclude chemistry technology. At present it becomes estimated that about 80% of all chemical products go through a catalytic stage in their creation of value chain.

Also the inhibitors (negative catalysts) attained a certain meaning in the chemical industry, by being used, if one normally like an explosionrunning reaction to be industrially used and controlled is (example: the polymerization of Metaldehyd from acetaldehyde) or if a certain by-product is to be excluded. Also within the range of the rust protection inhibitors are used.

If several products develop with reactions, the selectivity playsa catalyst a very important role. The catalyst is obtained in such a way selected that only that reaction is accelerated, the desired product. Impurities by by-products are avoided so to a large extent.

From the view of environmental protection becomes by the employment ofselective and active catalysts usually energy saved and the quantity of by-products reduces. For our environment the exhaust subsequent treatment is in addition, not less important in the industriellen production or in power stations. In case of the exhaustcatalytic procedures (e.g.in cars) unavoidable, dangerous substances are converted into fewer dangerous.

Katalysator
Catalyst

example: In the exhaust gas catalyst the breath poison carbon mono oxide ( CO) with oxygen (O 2) reacts to the greenhouse gas carbon dioxide (CO 2).

examples of catalysts

cerium iron (Ammonia synthesis), Raney nickel, platinum, rhodium, palladium, Vanadiumpentoxid and samarium oxide catalyzes the hydrogenation and dehydrogenation of ethanol.

Hopcalite, a group of catalysts from different metallic oxides, catalyze the oxidation from carbon monoxide to carbon dioxide at ambient temperature.

Vehicle catalyst: Most well-known example is the catalyst in the automobile for the reduction of the waste gas emission, with which the whole equipment is designated according to the chemically effective principle.

important one catalytic procedures

procedure product catalyst condition reactor
ammonia synthesis NH 3 Α-Eisen/Al 2 O 3 T = 450-500 °C; p = 25-40 MPa fixed bed reactor
methanol synthesis CH 3 OH CuO/Cr 2 O 3, ZnO/Cr 2 O 3 or CuO/Zn0 T = 210-280 °C; p = 6 MPa fixed bed reactor
sulfur outer deer only. H2 SO 4 V 2 O 5 /Tr of äger T = 400-500 °C fixed bed reactor
saltpeter outer deer only. (Ostwald procedure) HNO 3 platinum/rhodium T = 800 °C


literature

  • Ferdi Schüth: Key technology of the chemical industry: Heterogeneous catalysis.Chemistry in our time 40 (2), S. 92 - 103 (2006), ISSN 0009-2851
  • Michael Röper: Homogeneous catalysis in the chemical industry. Chemistry in our time 40 (2), S. 126 - 135 (2006), ISSN 0009-2851
  • Rainer Stürmer, Michael Breuer: Enzymes as catalysts.Chemistry and biology hand in hand. Chemistry in our time 40 (2), S. 104 - 111 (2006), ISSN 0009-2851

see also:

Autocatalysis, homogeneous catalysis, heterogeneous catalysis, catalyst poison, biocatalyst

 

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