In chemistry and biology, catalysis (in Greek meaning to annul) is the acceleration of the rate of a chemical reaction by means of a substance, called a catalyst, that is itself unchanged chemically by the overall reaction. The opposite of a catalyst is an inhibitor, which slows down the rate of a chemical reaction. Chemistry (in Greek: χημεία) is the science of matter and its interactions with energy and itself (see physics, biology). ... Biology is the science of life (from the Greek words bios = life and logos = reasoned account). ... A catalyst (Greek: καταλύτης, catalytis) is a substance that accelerates the rate of a chemical reaction, at some temperature, but without itself being transformed or consumed by the reaction (see also catalysis). ... An inhibitor is a type of effector that decreases or prevents a chemical reaction. ...

A common misunderstanding is that catalysis "makes the reaction happen", and 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. A catalyst (Greek: καταλύτης, catalytis) is a substance that accelerates the rate of a chemical reaction, at some temperature, but without itself being transformed or consumed by the reaction (see also catalysis). ... Thermodynamics (Greek: thermos = heat and dynamic = change) is the physics of energy, heat, work, entropy and the spontaneity of processes. ...

The mechanisms by which a catalyst speeds up a reaction are many, but they are all based on the reduction of the activation energy that is necessary to initiate the reaction. If you think of a reaction as a hill to be passed, the activation energy is the uphill part from the reactants' energy level to the energy level of the activated complex. The activated complex can then descend on either side of the reaction, either returning to the reactants or becoming products. In the hill example, catalysis functions as a tunnel, providing an easier way to the other side of the hill. The activation energy in chemistry is the energy needed by a system to initiate a particular process. ... An underground pedestrian tunnel between buildings at MIT. Note the utility pipes running along the ceiling. ...

Catalysts accelerate the chemical reaction by providing a lower energy pathway between the reactants and the 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. SI derived units are part of the SI system of measurement units and are derived from the seven SI base units. ... Katal is the SI derived unit for catalytic activity. ...

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. In chemistry, adsorption of a substance is its concentration on a particular surface. ... In computer networks, rate limiting is the function of controlling the maximum rate of traffic sent or received on a network interface. ...

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
  • Alkylation
• Industrial and automotive abatement of NO_x, CO, and hydrocarbons
• Nearly every chemical process associated with life!

The Haber Process (also Haber-Bosch process) is the reaction of nitrogen and hydrogen to produce ammonia. ... Ammonia is a chemical compound with the formula NH3. ... Steam reforming is a method of producing hydrogen. ... In chemistry, a hydrocarbon is a cleaning solution consisting only of carbon (C) and hydrogen (H). ... Methanol, also known as methyl alcohol or wood alcohol, is a chemical compound with chemical formula CH3OH. It is the simplest alcohol, and is a light, volatile, colourless, flammable, poisonous liquid that is used as an antifreeze, solvent, fuel, and as a denaturant for ethyl alcohol. ... Comparison between a clean Fischer-Tropsch diesel fuel (flask with clear liquid) and conventional No. ... Hydrogenation is a chemical reaction in which unsaturated bonds between carbon atoms are reduced by attachment of a hydrogen atom to each carbon. ... Sulfuric acid (British English: sulphuric acid), H2SO4, is a strong mineral acid. ... The chemical compound nitric acid (HNO3), otherwise known as aqua fortis, is a colorless, corrosive liquid, a toxic acid which can cause severe burns. ... Nodding donkey pumping an oil well near Sarnia, Ontario, 2001 Petroleum (from Greek petra – rock and oleum – oil), crude oil, sometimes colloquially called black gold, is a thick, dark brown or greenish flammable liquid, which exists in the upper strata of some areas of the Earths crust. ... In petroleum geology and chemistry, cracking is the process whereby complex organic molecules (e. ... Naphtha is a group of various volatile flammable liquid hydrocarbon mixtures used chiefly as solvents. ... Alkylation is the transfer of an alkyl group from one molecule to another. ...

See also

• Autocatalysis
• Metabolic pathway
• Surface chemistry
• Abzyme
• Dispersion (materials science)
• EC number
• Ozone hole
• Catalyst
• Albert Szent-Györgyi
• Ribozyme
• Enzyme
• Michaelis-Menten kinetics
• Catalytic converter (automobiles)