Catalysis
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In chemistry and biology, catalysis is the acceleration of the reaction rate of a chemical reaction by means of a substance, called a catalyst, that is itself unchanged chemically by the overall reaction. The word is derived from the Greek καταλειν or κατάλυσις meaning to annul or to untie or to pick up. The chinese symbol for catalyst is the same as the one for marriage broker.
Catalysts accelerate the chemical reaction by providing a lower energy pathway between the reactants and the reaction products. This usually involves the formation of one or more intermediates, which cannot be formed without the catalyst. The formation of this intermediate and subsequent reaction generally has a much lower activation energy barrier than is required for the direct reaction of reactants to products. The SI derived unit for measuring catalytic activity is the katal, which is moles per second. The degree of activity of a catalyst can also be described by the turn over number or TON and the catalytic efficiency by the turn over frequency (TOF). The biochemical equivalent is the enzyme unit.
The opposite of a catalyst is an inhibitor, which slows down the rate of a chemical reaction. In Autocatalysis a reactant or reaction product is itself the catalyst. Two types of catalysis are generally distinguished. In homogeneous catalysis the reactants and catalyst are in the same phase and in heterogeneous catalysis the catalyst is in a different phase than the reactants and products. A promoter is an accelerator of catalysis, but not a catalyst by itself.
In nature enzymes are catalysts in the Metabolic pathway. In biochemistry catalysis is also observed with Abzymes,Ribozymes and deoxyribozymes. Catalysis is at the heart of the Bombardier beetle defence mechanism.
The phrase catalysis was coined by Jöns Jakob Berzelius in 1835 who was the first to note that certain chemicals speed up a reaction. Other early chemists involved in catalysis were Alexander Mitscherlich who in 1831 referred to contact processes and Johann Wolfgang Döbereiner who spoke of contact action and whose lighter based on hydrogen and a platinum sponge became a hugh commercial success in the 1820’s.
Catalysis is a very important process from an industrial point of view since the production of most industrially important chemicals involve catalysis. The earliest commercial processes are the Haber process for ammonia synthesis and the Fischer-Tropsch synthesis. Research into catalysis is a major field in applied science, and involves many fields of chemistry, notably in organometallic chemistry, and physics. Catalysis is important in many aspects of environmental science from the catalytic converter in automobiles to the causes of the ozone hole.
Important catalytic processes
- Haber process
- Steam reforming of hydrocarbons to produce synthesis gas
- Methanol synthesis
- Fischer-Tropsch synthesis.
- Hydrogenation
- Sulfuric acid production
- Nitric acid production
- Petroleum refining and processing
- Catalytic cracking - breaking long-chain hydrocarbons into smaller pieces
- Naptha reforming
- Alkylation
- fuel cells
External links
- W.A. Herrmann Technische Universität presentation [1] (http://aci.anorg.chemie.tu-muenchen.de/wah/vortraege/catalysis.pdf)
- University of York catalyst pages [2] (http://www.uyseg.org/catalysis/pages/cat_frames.htm)de:Katalyse
es:Catálisis fr:Catalyse nl:Katalyse pt:Catálise sk:Katalýza zh:催化