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Encyclopedia > Catalyst
It has been suggested that this article or section be merged into Catalysis. (Discuss)


Generally, a catalyst is defined as any substance that changes the speed of a chemical reaction and does not appear in the final resultant product, and undergoes no (permanent) changes. Wikipedia does not have an article with this exact name. ... Generic graph showing the effect of a catalyst in an hypothetical exothermic chemical reaction. ...



In chemistry, a catalyst (Greek: καταλύτης, catalytēs) is a substance that decreases the activation energy of a chemical reaction (see also catalysis) without itself being changed at the end of the chemical reaction. Catalysts participate in reactions but are neither reactants nor products of the reaction they catalyse (a strange 'exception' is the process of autocatalysis). They work by providing an alternative pathway for the reaction to occur, thus reducing the activation energy and increasing the reaction rate. More generally, one may at times call anything that accelerates a reaction, without itself being consumed or changed, a "catalyst" (for example, a "catalyst for political change"). Water and steam are two different forms of the same chemical substance A chemical substance is any material with a definite chemical composition, no matter where it comes from. ... The sparks generated by striking steel against a flint provide the activation energy to initiate combustion in this Bunsen burner. ... A chemical reaction occurs when vapours of hydrogen chloride and ammonia meet to form a cloud of a new substance, ammonium chloride Chemical reaction is a process that results in the interconversion of chemical substances [1]. The substance or substances initially involved in a chemical reaction are called reactants. ... Generic graph showing the effect of a catalyst in an hypothetical exothermic chemical reaction. ... A single chemical reaction is said to have undergone autocatalysis, or be autocatalytic, if the reaction product is itself the catalyst for that reaction. ... The sparks generated by striking steel against a flint provide the activation energy to initiate combustion in this Bunsen burner. ... The reaction rate for a reactant or product in a particular reaction is defined as the fraction of the chemical that is formed or removed (in moles or mass units) per unit time per unit volume. ...


A promoter is an accelerator of catalysis, but not a catalyst by itself. An inhibitor inhibits the working of a catalyst. A reaction inhibitor is a substance that prevents or decreases the rate of a chemical reaction. ...

Contents

History

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 huge commercial success in the 1820’s. Jöns Jakob Berzelius Statue of Berzelius in the centre of Berzelii Park, Stockholm Jöns Jakob Berzelius (August 20, 1779 - August 7, 1848) was a Swedish chemist. ... Alexander Mitscherlich (b. ... Johann Wolfgang Döbereiner Johann Wolfgang Döbereiner (December 13, 1780 – March 24, 1849) was a German chemist. ... A metal naphtha lighter A lighter is a device used to create fire with the intent to ignite another substance such as a cigarette, smoking pipe, or charcoal in a grill. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ...


PUSH IT TO THE LIMIT!


Importance of Catalysis

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. The Haber Process (also Haber-Bosch process) is the reaction of nitrogen and hydrogen to produce ammonia. ... Ammonia is a compound of nitrogen and hydrogen with the formula NH3. ... Comparison between a clean Fischer-Tropsch diesel fuel (flask with clear liquid) and conventional No. ... Organometallic chemistry is the study of chemical compounds containing bonds between carbon and a metal. ... jecca is very beautiful!! Environmental science is the study of the interactions among the physical, chemical and biological components of the environment; with a focus on pollution and degradation of the environment related due to human activities; and the impact on biodiversity and sustainability from local and global development. ... Catalytic converter on a Saab 9-5. ... Image of the largest antarctic ozone hole ever recorded in September 2000. ...


Definitions

Catalysts generally react with one or more reactants to form a chemical intermediate that subsequently reacts to form the final reaction product, in the process regenerating the catalyst. The following is a typical reaction scheme, where C represents the catalyst, A and B are reactants, D is the product of the reaction of A and B:

A + C → AC (1)
B + AC → ABC (2)
ABC → CD (3)
CD → C + D (4)

Although the catalyst (C) is consumed by reaction 1, it is subsequently produced by reaction 4, so for the overall reaction:

A + B + C → D + C

the catalyst is neither consumed nor produced.


Catalysts and reaction energetics

Generic graph showing the effect of a catalyst in an hypothetical exothermic chemical reaction. Notice that the catalysed (red) pathway, despite having a lower activation energy, produces the same final result.
Generic graph showing the effect of a catalyst in an hypothetical exothermic chemical reaction. Notice that the catalysed (red) pathway, despite having a lower activation energy, produces the same final result.

Catalysts work by providing an (alternative) mechanism involving a different transition state and lower activation energy. The effect of this is that more molecular collisions have the energy needed to reach the transition state. Hence, catalysts can perform reactions that, albeit thermodynamically feasible, would not run without the presence of a catalyst, or perform them much faster, more specific, or at lower temperatures. This can be observed on a Boltzmann distribution and energy profile diagram. This means that catalysts reduce the amount of energy needed to start a chemical reaction. Image File history File links Catalyst_effect. ... Image File history File links Catalyst_effect. ... The sparks generated by striking steel against a flint provide the activation energy to initiate combustion in this Bunsen burner. ... The Maxwell-Boltzmann distribution is a probability distribution with applications in physics and chemistry. ...


Catalysts cannot make energetically unfavorable reactions possible — they have no effect on the chemical equilibrium of a reaction because the rate of both the forward and the reverse reaction are equally affected (see also thermodynamics). The net free energy change of a reaction is the same whether a catalyst is used or not; the catalyst just makes it easier to activate. Chemical equilibrium is the state in which the concentrations of the reactants and products have no net change over time. ... Thermodynamics (from the Greek thermos meaning heat and dynamics meaning power) is a branch of physics that studies the effects of changes in temperature, pressure, and volume on physical systems at the macroscopic scale by analyzing the collective motion of their particles using statistics. ...


The SI derived unit for measuring the catalytic activity of a catalyst 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. 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. ... Turnover Frequency (TOF) Rate of conversion is given as the number of moles converted or produced per unit weight and unit time. ... An enzyme unit is the amount of enzyme that catalyzes the transformation of 1 micromole of substance per minute at 30°C. It is commonly used to measure the specific activity of an enzyme. ...


Types of catalysts

Catalysts can be either heterogeneous or homogeneous. Biocatalysis is often seen as a separate group. Look up Heterogeneous in Wiktionary, the free dictionary. ... Biocatalysis can be defined as the utilization of natural catalysts, called enzymes, to perform chemical transformations on organic compounds. ...


Heterogeneous catalysts are present in different phases from the reactants (for example, a solid catalyst in a liquid reaction mixture), whereas homogeneous catalysts are in the same phase (for example, a dissolved catalyst in a liquid reaction mixture). In the physical sciences, a phase is a set of states of a macroscopic physical system that have relatively uniform chemical composition and physical properties (i. ... In chemistry, the reactants are the substances that exist at the start of a chemical reaction. ... In jewelry, a solid gold piece is the alternative to gold-filled or gold-plated jewelry. ... A liquid will usually assume the shape of its container. ... For the connotation of the term relating to chemistry, see Solvation. ...


Heterogeneous catalysts

A simple model for heterogeneous catalysis involves the catalyst providing a surface on which the reactants (or substrates) temporarily become adsorbed. Bonds in the substrate become weakened sufficiently for new bonds to be created. The bonds between the products and the catalyst are weaker, so the products are released. Different possible mechanisms for reactions on surfaces are known, depending on how the adsorption takes place (Langmuir-Hinshelwood and Eley-Rideal). Look up Heterogeneous in Wiktionary, the free dictionary. ... An open surface with X-, Y-, and Z-contours shown. ... In biochemistry, a substrate is a molecule which is acted upon by an enzyme. ... Adsorption is a process that occurs when a liquid or gas (called adsorbate) accumulates on the surface of a solid or liquid (adsorbent), forming a molecular or atomic film (adsorbate). ... A chemical bond is the physical phenomenon of chemical substances being held together by attraction of atoms to each other through sharing, as well as exchanging, of electrons or electrostatic forces. ... By reactions on surfaces it is understood reactions in which at least one of the steps of the reaction mechanism is the adsorption of one or more reactants. ...


For example, in the Haber process to manufacture ammonia, finely divided iron acts as a heterogeneous catalyst. Active sites on the metal allow partial weak bonding to the reactant gases, which are adsorbed onto the metal surface. As a result, the bond within the molecule of a reactant is weakened and the reactant molecules are held in close proximity to each other. In this way the particularly strong triple bond in nitrogen is weakened and the hydrogen and nitrogen molecules are brought closer together than would be the case in the gas phase, so the rate of reaction increases. The Haber Process (also Haber-Bosch process) is the reaction of nitrogen and hydrogen to produce ammonia. ... Ammonia is a compound of nitrogen and hydrogen with the formula NH3. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... A gas is one of the five main phases of matter (after solid and liquid, and followed by plasma and Bose-Einstein Condensate) and, that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... In chemistry, a molecule is adsorbed onto a surface when temporary bonds are formed between the surface and the molecule. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ...


Other heterogeneous catalysts include vanadium(V) oxide in the Contact process, nickel in the manufacture of margarine, alumina and silica in the cracking of alkanes and platinum rhodium palladium in catalytic converters. Vanadium(V) oxide (V2O5), commonly known as vanadium pentoxide, is the most important compound of vanadium. ... The contact process is the current method of producing sulphuric acid in the high concentrations needed for industrial processes. ... General Name, Symbol, Number nickel, Ni, 28 Chemical series transition metals Group, Period, Block 10, 4, d Appearance lustrous, metallic Atomic mass 58. ... Margarine, as a generic term, can indicate any of a wide range of butter-substitutes. ... Aluminium oxide (or aluminum oxide) (Al2O3) is a chemical compound of aluminium and oxygen. ... The chemical compound silicon dioxide, also known as silica, is the oxide of silicon, chemical formula SiO2. ... Cracking-divides a group’s voters into other districts, where they will be ineffective minorities; and kidnapping places two incumbents from the same party in the same district. ... An alkane in organic chemistry is a type of hydrocarbon in which the molecule has the maximum possible number of hydrogen atoms and so has no double bonds (they are saturated). ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... Rh redirects here. ... General Name, Symbol, Number palladium, Pd, 46 Chemical series transition metals Group, Period, Block 10, 5, d Appearance silvery white metallic Atomic mass 106. ... In an automobiles exhaust system, a catalytic converter provides an environment for a chemical reaction where unburned hydrocarbons completely combust. ...


In car engines, incomplete combustion of the fuel produces carbon monoxide, which is toxic. The electric spark and high temperatures also allow oxygen and nitrogen to react and form nitric oxide and nitrogen dioxide, which are responsible for photochemical smog and acid rain. Catalytic converters reduce such emissions by adsorbing CO and NO onto catalytic surface, where the gases undergo a redox reaction. Carbon dioxide and nitrogen are desorbed from the surface and emitted as relatively harmless gases: Combustion or burning is a complex sequence of chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. ... Fuel is any material that is capable of releasing energy when its chemical or physical structure is changed or converted. ... Carbon monoxide, with the chemical formula CO, is a colourless, odourless, and tasteless gas. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... The chemical compound nitric oxide is a gas with chemical formula NO. It is an important signaling molecule in the body of mammals including humans, one of the few gaseous signaling molecules known. ... [1] R-phrases , S-phrases , , , , , Supplementary data page Structure and properties n, εr, etc. ... Victorian London was notorious for its thick smogs, or pea-soupers, a fact that is often recreated to add an air of mystery to a period costume drama. ... The effects of acid rain in the Jizera Mountains of the Czech Republic Acid rain (or more accurately acid precipitation)[1] occurs when sulfur dioxide and nitrogen oxides are emitted into the atmosphere, undergo chemical transformations and are absorbed by water droplets in clouds. ... Carbon monoxide, with the chemical formula CO, is a colourless, odourless, and tasteless gas. ... The chemical compound nitric oxide is a gas with chemical formula NO. It is an important signaling molecule in the body of mammals including humans, one of the few gaseous signaling molecules known. ... The most fundamental reactions in chemistry are the redox processes. ... Carbon dioxide is a chemical compound composed of one carbon and two oxygen atoms. ...

2CO + 2NO → 2CO2 + N2

Homogeneous catalysts

In homogeneous catalysis the catalyst is a molecule which facilitates the reaction. The reactant(s) coordinate to the catalyst (or vice versa), are transformed to product(s), which are then released from the catalyst. In chemistry, a molecule is an aggregate of at least two atoms in a definite arrangement held together by special forces. ... See Cartesian coordinate system or Coordinates (elementary mathematics) for a more elementary introduction to this topic. ...


Examples of homogeneous catalysts are H+(aq) which acts as a catalyst in esterification, and chlorine free radicals in the break down of ozone. Chlorine free radicals are formed by the action of ultraviolet radiation on chlorofluorocarbons (CFCs). They react with ozone forming oxygen molecules and regenerating chlorine free radicals: General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... Esterification is the general name for a chemical reaction in which two chemicals (typically an alcohol and an acid) form an ester as the reaction product. ... General Name, Symbol, Number chlorine, Cl, 17 Chemical series halogens Group, Period, Block 17, 3, p Appearance yellowish green Atomic mass 35. ... In chemistry free radicals are uncharged atomic or molecular species with unpaired electrons or an otherwise open shell configuration. ... For other uses, see Ozone (disambiguation). ... To meet Wikipedias quality standards, this article or section may require cleanup. ... Radiation in Physics is the process of emitting energy in the form of waves or particles. ... For other uses, see CFC (disambiguation). ...

Cl + O3 → ClO + O2
ClO + O → Cl + O2

Biocatalysts

In nature enzymes are catalysts in the metabolic pathway. In biochemistry catalysis is also observed with abzymes, ribozymes and deoxyribozymes. In biocatalysis enzymes are used as catalyst in organic chemistry. Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... In biochemistry, a metabolic pathway is a series of chemical reactions occurring within a cell, catalyzed by enzymes, resulting in either the formation of a metabolic product to be used or stored by the cell, or the initiation of another metabolic pathway (then called a flux generating step). ... This article or section does not cite its references or sources. ... An abzyme (from antibody and enzyme), also called catmab (from catalytic monoclonal antibody), is a monoclonal antibody with catalytic activity. ... A ribozyme (from ribonucleic acid enzyme, also called RNA enzyme or catalytic RNA) is an RNA molecule that catalyzes a chemical reaction. ... Deoxyribozymes or DNA enzymes or catalytic DNA, or DNAzymes are DNA molecules with catalytic action. ... Biocatalysis can be defined as the utilization of natural catalysts, called enzymes, to perform chemical transformations on organic compounds. ... Organic chemistry is a specific discipline within the subject of chemistry. ...


Poisoning of a Catalyst

Main article: catalyst poisoning

A catalyst can be poisoned if another compound reacts with it and bonds chemically (similar to an inhibitor) but does not release, or chemically alters the catalyst. This effectively destroys the usefulness of the catalyst, as it cannot participate in the reaction with which it was supposed to catalyse. Catalyst poisoning refers to the effect that a catalyst can be poisoned if it reacts with another compound that bonds chemically (similar to an inhibitor) but does not release, or chemically alters the catalyst. ...


Commonly used catalysts

Estimates are that 60% of all commercially produced chemical products involve catalysts at some stage in the process of their manufacture.[1]


Some of the most famous catalysts ever developed are:

Some examples of (famous) catalysts that perform specific transformations on functional groups: Catalytic converter on a Saab 9-5. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... Rh redirects here. ... The Haber Process (also Haber-Bosch process) is the reaction of nitrogen and hydrogen to produce ammonia. ... Ammonia is a compound of nitrogen and hydrogen with the formula NH3. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ...

These given examples show that different catalysts perform other transformations on the same functional groups, where the reaction would not run, run very slow, or would not run in a specific manner without the presence of the catalyst A synonym for the more widely accepted term, alkene. ... A Ziegler-Natta catalyst is a reagent used in the production of unbranched, stereoregular vinyl polymers. ... POLYETHYLENE [[In the polymer industry the name is sometimes shortened to PE, . The ethylene molecule connected by a double bond, thus: Polyethylene is created through polymerization of ethylene. ... Polypropylene lid of a Tic Tacs box, with a living hinge and the resin identification code under its flap Polypropylene or polypropene (PP) is a thermoplastic polymer, used in a wide variety of applications, including food packaging, textiles, laboratory equipment, loudspeakers, automotive components, and polymer banknotes. ... Grubbs Catalyst is named after the chemist by whom it was first synthesized, Robert H. Grubbs. ... Olefin metathesis or transalkylidenation (in some literature, a disproportionation) is an organic reaction which involves redistribution of olefinic (alkene) bonds. ...


The most effective catalysts are usually transition metals or transition metal complexes. In chemistry, the term transition metal (sometimes also called a transition element) has two possible meanings: It commonly refers to any element in the d-block of the periodic table, including zinc, cadmium and mercury. ... Synthesis of copper(II)-tetraphenylporphine, a metal complex, from tetraphenylporphine and copper(II) acetate monohydrate. ...


Catalytic processes

It has been suggested that this article or section be merged with Acid catalysis. ... Catalytic converter on a Saab 9-5. ... General Name, Symbol, Number platinum, Pt, 78 Chemical series transition metals Group, Period, Block 10, 6, d Appearance grayish white Atomic mass 195. ... Rh redirects here. ... A fuel cell is an electrochemical device similar to a battery, but differing from the latter in that it is designed for continuous replenishment of the reactants consumed; i. ... Comparison between a clean Fischer-Tropsch diesel fuel (flask with clear liquid) and conventional No. ... The Haber Process (also Haber-Bosch process) is the reaction of nitrogen and hydrogen to produce ammonia. ... Ammonia is a compound of nitrogen and hydrogen with the formula NH3. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number iron, Fe, 26 Chemical series transition metals Group, Period, Block 8, 4, d Appearance lustrous metallic with a grayish tinge Atomic mass 55. ... Hydrogenation is a chemical reaction in which unsaturated bonds between carbon atoms are reduced by attachment of a hydrogen atom to each carbon. ... 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 with a distinctive odor that is somewhat sweeter than ethanol (ethyl alcohol). ... The chemical compound nitric acid (HNO3), otherwise known as aqua fortis or spirit of nitre, is an aqueous solution of hydrogen nitrate (anhydrous nitric acid). ... Pumpjack pumping an oil well near Sarnia, Ontario Ignacy Łukasiewicz - inventor of the refining of kerosene from crude oil. ... Alkylation is the transfer of an alkyl group from one molecule to another. ... 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 primarily as feedstocks in refineries for the reforming process and in the petrochemical industry for the production of olefins in steam crackers. ... Steam reforming, or catalytic oxidation, is a method of producing hydrogen from hydrocarbons. ... In chemistry, a hydrocarbon is a cleaning solution consisting only of carbon (C) and hydrogen (H). ... Syngas (from synthesis gas) is the name given to gasses of varying composition that are generated in coal gasification and some types of waste-to-energy facilities. ... Sulfuric acid (British English: sulphuric acid), H2SO4, is a strong mineral acid. ... In organic chemistry, transesterification is the process of exchanging the alkoxy group of an ester compound by another alcohol. ... A Ziegler-Natta catalyst is a reagent used in the production of unbranched, stereoregular vinyl polymers. ...

See also

  1. ^ "Recognizing the Best in Innovation: Breakthrough Catalyst". R&D Magazine, September 2005, pg 20.

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Catalysts participate in reactions but are neither reactants nor products of the reaction they catalyse (a strange 'exception' is the process of autocatalysis).
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