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In chemistry and biology, catalysis is the acceleration of the rate of a chemical reaction by a substance, called a catalyst, that is itself unchanged by the overall reaction. A common misunderstanding is that catalysis "makes the reaction happen": that the reaction would not otherwise proceed without the presence of the catalyst.
In biologically- or industrially-useful timescales, this may be true in a limited sense. However, a catalyst cannot make a thermodynamically unfavorable reaction proceed. Rather, it can only speed up a reaction that is already thermodynamically favorable. Such a reaction in the absence of a catalyst would proceed, even without the catalyst, although perhaps too slowly to be observed or of use in a given context.
Catalysts accelerate the chemical reaction by providing a lower energy pathway between the reactants and the products. This usually involves the formation of an intermediate, 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.
Catalysis is a very important process from an industrial point of view since the production of most industrially important chemicals involve catalysis. Research into catalysis is a major field in applied science, and involves many fields of chemistry and physics.
Two types of catalysis are generally distinguished. In homogeneous catalysis the reactants and catalyst are in the same phase. For example acids (H+ ion donors) are common catalysts in many aqueous reactions. In this case both the reactants and the catalysts are in the aqueous phase. In heterogeneous catalysis the catalyst is in a different phase than the reactants and products. Usually, the catalyst is a solid and the reactants and products are gases or liquids. In order for the reaction to occur one or more of the reactants must diffuse to the catalyst surface and adsorb onto it. After reaction, the products must desorb from the surface and diffuse away from the solid surface. Frequently, this transport of reactants and products from one phase to another plays a dominant role in limiting the rate of reaction. Understanding these transport phenomena is an important area of heterogeneous catalyst research.
1 Important catalytic processes
- The Haber process for ammonia synthesis
- Steam reforming of hydrocarbons to produce synthesis gas
- Methanol synthesis
- Fischer-Tropsch synthesis
- Hydrogenation/dehydrogenation of organic compounds
- Sulfuric acid production
- Nitric acid production
- Maleic anhydride production
- Petroleum refining and processing
- Hydrotreating - hydrogenation of hydrocarbons and removal of organic sulfur, nitrogen, oxygen, and metals
- Catalytic cracking - breaking long-chain hydrocarbons into smaller pieces
- Naptha reforming
- AlkylationAlkylation is the transfer of an alkyl group from one molecule to another. In a standard Refinery Process,Alkylation system combines low-molecular-weight olefins (primarily a mixture of propylene and butylene) with isobutene in the presence of a catalyst,
- Industrial and automotive abatement of NOx, CO, and hydrocarbons
- Nearly every chemical process associated with life!
2 See also
- Metabolic pathwayIn biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell, catalyzed by enzymes, and resulting in either the formation of a metabolic product to be used or stored by the cell ( metabolic sink), or the initiation of ano
- Surface chemistrySurface chemistry is the study of chemical phenomena that occur at the interface of two phases, usually between a gas and a solid or between a liquid and a solid. One important field of surface chemical research is related to surface functionalization, wh
- AbzymeAn abzyme (from antibody and enzyme), also called catmab (from catalytic monoclonal antibody , is a monoclonal antibody with catalytic activity. Abzymes are usually artificial constructs, but are also found in normal humans (anti-vasoactive intestinal pep
- Dispersion (materials science)In materials science, dispersion is the fraction of atoms of a material exposed to the surface. In general: D N ''N where D is the dispersion, N is the number of surface atoms and N is the total number of atoms of the material. Dispersion is an important
- EC numberEC numbers Enzyme Commission numbers are a numerical classification scheme for enzymes, based on the chemical reactions they catalyze. As a system of enzyme nomenclature every EC number is associated with a recommended name for the respective enzyme.
- Ozone hole
- Catalyst
- Albert Szent-Györgyi
- Ribozyme
- Enzyme
- Michaelis-Menten kinetics
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