Catalysis is the process by which the rate of a chemical reaction (or biological process) is increased by means of the addition of a species known as a catalyst to the reaction. What makes a catalyst different from a chemical reagent is that whilst it participates in the reaction, is not consumed in the reaction. That is, the catalyst may undergo several chemical transformations during the reaction, but at the conclusion of the reaction, the catalyst is regenerated unchanged. As a catalyst is regenerated in a reaction, often only a very small amount is needed to increase the rate of the reaction.
A catalyst works by providing an alternative reaction pathway to the reaction product. The rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst. The lower the activation energy, the faster the rate of the reaction.
A real example is the disproportionation of hydrogen peroxide to give water and oxygen: 2 H2O2 → 2 H2O + O2
Whilst the above reaction is favoured in the sense that reaction products are more stable than the starting material, the reaction is slow. This can be seen by the fact that hydrogen peroxide is often available for purchase on the high-street in bottles as a disinfectant.
However, upon the addition of a small amount of manganese dioxide, the hydrogen peroxide undergoes a rapid reaction, which can be readily seen by the effervescence of oxygen.[citation needed] The manganese dioxide may be recovered unchanged, and re-used indefinitely, and thus is not consumed in the reaction. Accordingly, manganese dioxide catalyses this reaction.
In a more general sense, anything that increases the rate of any process is commonly called a "catalyst" (From the Greekκαταλύειν, meaning to annul or to untie or to pick up). For example a matchmaker might be called a catalyst, as he or she brings two people together who otherwise might not meet, with the matchmaker being unaltered by the matching process.
The opposite of a catalyst is an inhibitor which slows the rate of a reaction without itself being consumed.
Contents
1 History
2 Typical mechanism
3 Catalytic cycles
4 Catalysts and reaction energetics
4.1 Autocatalysis
5 Types of catalysts
5.1 Heterogeneous catalysts
5.2 Homogeneous catalysts
5.3 Biocatalysts
5.4 Electrocatalysts
6 Significance
7 Notable examples
8 New directions - organocatalysis
9 Catalytic processes
10 See also
11 References
12 External links
2 Typical mechanism
3 Catalytic cycles
4 Catalysts and reaction energetics
4.1 Autocatalysis
5 Types of catalysts
5.1 Heterogeneous catalysts
5.2 Homogeneous catalysts
5.3 Biocatalysts
5.4 Electrocatalysts
6 Significance
7 Notable examples
8 New directions - organocatalysis
9 Catalytic processes
10 See also
11 References
12 External links
Surface and Nanomolecular Catalysis
Highlighting new instrumentation and experimental techniques-including high-throughput experimentation and combinatorial approaches-that are being employed to observe chemical reactions and molecular properties at the nanoscale, leading scientists from a diverse range of fields reveal new insights into the surface chemistry of catalysts and the reaction mechanisms that
http://rapidshare.com/files/22170585/SNC.rar.html
Highlighting new instrumentation and experimental techniques-including high-throughput experimentation and combinatorial approaches-that are being employed to observe chemical reactions and molecular properties at the nanoscale, leading scientists from a diverse range of fields reveal new insights into the surface chemistry of catalysts and the reaction mechanisms that
http://rapidshare.com/files/22170585/SNC.rar.html
