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that utilizes a low-temperature oxidation catalyst to convert
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...
to less toxic
carbon dioxide Carbon dioxide (chemical formula ) is a colorless gas with a density about 53% higher than that of dry air. Carbon dioxide molecules consist of a carbon atom covalent bond, covalently double bonded to two oxygen atoms. It occurs naturally in At ...

carbon dioxide
at room temperature. It can also remove
formaldehyde Formaldehyde ( , also ) ( systematic name methanal) is a naturally occurring organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen che ...
from the air. Catalysis () is the process of increasing the reaction rate, rate of a
chemical reaction A chemical reaction is a process that leads to the IUPAC nomenclature for organic transformations, chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the posit ...
by adding a substance known as a catalyst (). Catalysts are not consumed in the catalyzed reaction but can act repeatedly. Often only very small amounts of catalyst are required. The global demand for catalysts in 2010 was estimated at approximately US$29.5 billion.


General principles


Illustration

Illustrative is the
disproportionation In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, structure, properties, behavior and the changes they underg ...
of
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid, slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as ...

hydrogen peroxide
to water and
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
: :2 HO → 2 HO + O This reaction proceeds because the reaction products are more stable than the starting material. The uncatalysed reaction is slow. In fact, the decomposition of hydrogen peroxide is so slow that hydrogen peroxide solutions are commercially available. This reaction is strongly affected by catalysts such as
manganese dioxide Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

manganese dioxide
, or the enzyme
peroxidase Peroxidases or peroxide reductases ( EC numberbr>1.11.1.x are a large group of enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act ...
in organisms. Upon the addition of a small amount of
manganese dioxide Manganese dioxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese Manganese is a chemical element Image:Simple Periodic Table Chart- ...

manganese dioxide
, the hydrogen peroxide reacts rapidly. This effect is readily seen by the
effervescence Image:Soda bubbles macro.jpg, Bubbles of carbon dioxide float to the surface of a Soft drink#Carbonated drinks, carbonated soft drink. Effervescence is the escape of gas from an aqueous solution and the foaming or fizzing that results from that rel ...
of oxygen. The manganese dioxide is not consumed in the reaction, and thus may be recovered unchanged, and re-used indefinitely. Accordingly, manganese dioxide ''catalyses'' this reaction.


Units

The
SI derived unit SI derived units are units of measurement ' Measurement is the number, numerical quantification (science), quantification of the variable and attribute (research), attributes of an object or event, which can be used to compare with other objects or ...
for measuring the catalytic activity of a catalyst is the
katal The katal (symbol: kat) is the unit of catalytic activity in the International System of Units International is an adjective (also used as a noun) meaning "between nations". International may also refer to: Music Albums * International (Kevin ...
, which is quantified in moles per second. The productivity of a catalyst can be described by the
turnover numberTurnover number has two different meanings: In enzymology Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistr ...
(or TON) and the catalytic activity by the ''turn over frequency'' (TOF), which is the TON per time unit. The biochemical equivalent is the
enzyme unitThe enzyme unit, or international unit for enzyme (symbol U, sometimes also IU) is a unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a ...
. For more information on the efficiency of enzymatic catalysis, see the article on ''
enzymes Enzymes () are protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including E ...
''.


Typical mechanism

In general, chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternative reaction pathway - or mechanism - with a lower
activation energy provide the activation energy to initiate combustion in this Bunsen burner. The blue flame sustains itself after the sparks stop because the continued combustion of the flame is now energetically favorable. In chemistry Chemistry is the scie ...

activation energy
than the non-catalyzed mechanism. In catalyzed mechanisms, the catalyst usually reacts to form an intermediate, which then regenerates the original catalyst in a process. Catalysts generally react with one or more reactants to form intermediates that subsequently give the final reaction product, in the process regenerating the catalyst. The following is a typical reaction scheme, where ''C'' represents the catalyst, X and Y are reactants, and Z is the product of the reaction of X and Y: Although the catalyst is consumed by reaction , it is subsequently produced by reaction . As a catalyst is regenerated in a reaction, often only small amounts are needed to increase the rate of the reaction. In practice, however, catalysts are sometimes consumed in secondary processes. The catalyst does often appear in the
rate equation The rate law or rate equation for a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter ha ...
. For example, if the
rate-determining step In chemical kinetics Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is to be contrasted with thermodynamics, which deals with the dire ...
in the above reaction scheme is the first step
X + C → XC, the catalyzed reaction will be second order with rate equation v = k C], which is proportional to the catalyst concentration However remains constant during the reaction so that the catalyzed reaction is pseudo-first order: v = k where k = k As an example of a detailed mechanism at the microscopic level, in 2008 Danish researchers first revealed the sequence of events when
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
and
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
combine on the surface of
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compoun ...
(TiO, or ''titania'') to produce water. With a time-lapse series of
scanning tunneling microscopy A scanning tunneling microscope (STM) is a type of microscope used for imaging surfaces at the atomic level. Its development in 1981 earned its inventors, Gerd Binnig and Heinrich Rohrer, then at IBM Research – Zurich, IBM Zürich, the Nobel Pr ...
images, they determined the molecules undergo
adsorption of multilayer adsorption is a random distribution of molecules on the material surface. Adsorption is the adhesion Adhesion is the tendency of dissimilar Particle, particles or interface (matter), surfaces to cling to one another (Cohesion ...

adsorption
, dissociation and
diffusion File:DiffusionMicroMacro.gif, 250px, Diffusion from a microscopic and macroscopic point of view. Initially, there are solute molecules on the left side of a barrier (purple line) and none on the right. The barrier is removed, and the solute diff ...

diffusion
before reacting. The intermediate reaction states were: HO, HO, then HO and the final reaction product (), after which the water molecule desorbs from the catalyst surface.


Reaction energetics

Image:CatalysisScheme.png, upright=1.25, Generic potential energy diagram showing the effect of a catalyst in a hypothetical exothermic chemical reaction X + Y to give Z. The presence of the catalyst opens a different reaction pathway (shown in red) with a lower activation energy. The final result and the overall thermodynamics are the same. Catalysts work by providing an (alternative) mechanism involving a different transition state and lower
activation energy provide the activation energy to initiate combustion in this Bunsen burner. The blue flame sustains itself after the sparks stop because the continued combustion of the flame is now energetically favorable. In chemistry Chemistry is the scie ...

activation energy
. Consequently, more molecular collisions have the energy needed to reach the transition state. Hence, catalysts can enable reactions that would otherwise be blocked or slowed by a kinetic barrier. The catalyst may increase reaction rate or selectivity, or enable the reaction at lower temperatures. This effect can be illustrated with an
energy profileFor a chemical reaction or process an energy profile (or reaction coordinate diagram) is a theoretical representation of a single energetic pathway, along the reaction coordinate, as the reactants are transformed into products. Reaction coordinate d ...
diagram. In the catalyzed
elementary reactionAn elementary reaction is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having cons ...
, catalysts do not change the extent of a reaction: they have no effect on the
chemical equilibrium In a chemical reaction, chemical equilibrium is the state in which both reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system ...
of a reaction because the rate of both the forward and the reverse reaction are both affected (see also
thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, entropy, and the physical properties of matter and radiation. The behavior of these quantities is governed by ...

thermodynamics
). The
second law of thermodynamics The second law of thermodynamics establishes the concept of entropy Entropy is a scientific concept, as well as a measurable physical property that is most commonly associated with a state of disorder, randomness, or uncertainty. The term an ...
describes why a catalyst does not change the chemical equilibrium of a reaction. Suppose there was such a catalyst that shifted an equilibrium. Introducing the catalyst to the system would result in a reaction to move to the new equilibrium, producing energy. Production of energy is a necessary result since reactions are spontaneous only if
Gibbs free energy In thermodynamics Thermodynamics is a branch of physics that deals with heat, Work (thermodynamics), work, and temperature, and their relation to energy, radiation, and physical properties of matter. The behavior of these quantities is governe ...
is produced, and if there is no energy barrier, there is no need for a catalyst. Then, removing the catalyst would also result in reaction, producing energy; i.e. the addition and its reverse process, removal, would both produce energy. Thus, a catalyst that could change the equilibrium would be a
perpetual motion machine 's 1618 "water screw" perpetual motion machine from a 1660 wood engraving. It is widely credited as the first attempt to describe such a device in order to produce useful work, that of driving millstones. Perpetual motion is the motion of bodies ...
, a contradiction to the laws of thermodynamics. Thus, catalyst does not alter the equilibrium constant. (A catalyst can however change the equilibrium concentrations by reacting in a subsequent step. It is then consumed as the reaction proceeds, and thus it is also a reactant. Illustrative is the base-catalysed
hydrolysis Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

hydrolysis
of
ester An ester is a chemical compound derived from an acid (organic or inorganic) in which at least one –OH hydroxyl group is replaced by an –O– alkyl (alkoxy) group, as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

ester
s, where the produced
carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with R referring to the alkyl, alkenyl, aryl, or other group. Carboxy ...
immediately reacts with the base catalyst and thus the reaction equilibrium is shifted towards hydrolysis.) The catalyst stabilizes the transition state more than it stabilizes the starting material. It decreases the kinetic barrier by decreasing the ''difference'' in energy between starting material and transition state. It does not change the energy difference between starting materials and products (thermodynamic barrier), or the available energy (this is provided by the environment as heat or light).


Related concepts

Some so-called catalysts are really precatalysts. Precatalysts convert to catalysts in the reaction. For example,
Wilkinson's catalyst Wilkinson's catalyst is the common name for chloridotris(triphenylphosphine)rhodium(I), a coordination complex of rhodium Rhodium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic tabl ...
RhCl(PPh) loses one triphenylphosphine ligand before entering the true catalytic cycle. Precatalysts are easier to store but are easily activated
in situ ''In situ'' (; often not italicized in English) is a Latin Latin (, or , ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken in the area around Rome, known as ...
. Because of this preactivation step, many catalytic reactions involve an
induction period An induction period in chemical kinetics Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions. It is to be contrasted with thermodynamics, which ...
. Chemical species that improve catalytic activity are called co-catalysts (cocatalysts) or promoters in cooperative catalysis. In tandem catalysis two or more different catalysts are coupled in a one-pot reaction. In
autocatalysis A single chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical A chemical substance is a form of matter having constant chemical comp ...
, the catalyst ''is'' a product of the overall reaction, in contrast to all other types of catalysis considered in this article. The simplest example of autocatalysis is a reaction of type A + B → 2 B, in one or in several steps. The overall reaction is just A → B, so that B is a product. But since B is also a reactant, it may be present in the rate equation and affect the reaction rate. As the reaction proceeds, the concentration of B increases and can accelerate the reaction as a catalyst. In effect, the reaction accelerates itself or is autocatalyzed. An example is the hydrolysis of an
ester An ester is a chemical compound derived from an acid (organic or inorganic) in which at least one –OH hydroxyl group is replaced by an –O– alkyl (alkoxy) group, as in the substitution reaction of a carboxylic acid and an alcohol. Glycerides ...

ester
such as
aspirin Aspirin, also known as acetylsalicylic acid (ASA), is a medication A medication (also referred to as medicine, pharmaceutical drug, medicinal drug or simply drug) is a drug used to medical diagnosis, diagnose, cure, therapy, treat, or prev ...

aspirin
to a
carboxylic acid A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with R referring to the alkyl, alkenyl, aryl, or other group. Carboxy ...
and an
alcohol File:Alcohol general.svg, upright=0.8, The bond angle between a hydroxyl group (-OH) and a chain of carbon atoms (R) In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated ...

alcohol
. In the absence of added acid catalysts, the carboxylic acid product catalyzes the hydrolysis.


Classification

Catalysis may be classified as either homogeneous or heterogeneous. A
homogeneous catalysisIn chemistry, homogeneous catalysis is catalysis in a solution by a soluble catalyst. Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants, principally in solution. In contrast, heterogeneous catalysis ...
is one whose components are dispersed in the same phase (usually gaseous or liquid) as the
reactant 200px, Reactants, such as sulfur (''pictured''), are the starting materials that are used in chemical reactions. A reagent is a substance or compound added to a system to cause a chemical reaction A chemical reaction is a process that leads ...
's molecules. A
heterogeneous catalysis of ethene on a catalytic solid surface (1) Adsorption (2) Reaction (3) Desorption In chemistry, heterogeneous catalysis is catalysis where the Phase (matter), phase of catalysts differs from that of the reactants or product (chemistry), products ...
is one where the reaction components are not in the same phase.
Enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates int ...

Enzyme
s and other biocatalysts are often considered as a third category. Similar mechanistic principles apply to heterogeneous, homogeneous, and biocatalysis.


Heterogeneous catalysis

Heterogeneous catalysts act in a different
phase Phase or phases may refer to: Science * State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter) In the physical sciences, a phase is a region of space (a thermodynamic system A thermodynamic system is a ...
than the
reactants Image:SulfurReagent.jpg, 200px, Reactants, such as sulfur (''pictured''), are the starting materials that are used in chemical reactions. A reagent is a substance or compound added to a system to cause a chemical reaction, or added to test if a ...
. Most heterogeneous catalysts are
solid Solid is one of the four fundamental states of matter (the others being liquid, gas and plasma). The molecules in a solid are closely packed together and contain the least amount of kinetic energy. A solid is characterized by structural ...

solid
s that act on substrates in a
liquid A liquid is a nearly incompressible In fluid mechanics or more generally continuum mechanics, incompressible flow (isochoric process, isochoric flow) refers to a fluid flow, flow in which the material density is constant within a fluid parc ...

liquid
or gaseous
reaction mixture A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and t ...
. Important heterogeneous catalysts include
zeolite Zeolites are microporous, aluminosilicate mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (g ...

zeolite
s,
alumina Aluminium oxide is a chemical compound of aluminium and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic ta ...
, higher-order oxides, graphitic carbon,
transition metal In chemistry, the term transition metal (or transition element) has three possible definitions: * The IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations tha ...
oxide of rutile Rutile is a mineral composed primarily of titanium dioxide (TiO2), and is the most common natural form of TiO2. Other rarer polymorphs of TiO2 are known, including anatase, akaogiite, and brookite. Rutile has one of the highest re ...
s, metals such as
Raney nickel Raney nickel , also called spongy nickel, is a fine-grained solid composed mostly of nickel derived from a nickel–aluminium Aluminium (aluminum in American English, American and Canadian English) is a chemical element with the Symbol ( ...

Raney nickel
for hydrogenation, and
vanadium(V) oxide Vanadium(V) oxide (''vanadia'') is the inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition ...

vanadium(V) oxide
for oxidation of
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a Toxicity, toxic gas responsible for the smell of burnt matches. It is released naturally by vol ...
into
sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide) is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an industrial scale as a precursor to s ...
by the so-called . Diverse mechanisms for
reactions on surfaces Reactions on surfaces are reactions in which at least one of the steps of the reaction mechanism is the adsorption of multilayer adsorption is a random distribution of molecules on the material surface. Adsorption is the adhesion Adhesion ...
are known, depending on how the adsorption takes place ( Langmuir-Hinshelwood, Eley-Rideal, and Mars- van Krevelen). The total surface area of solid has an important effect on the reaction rate. The smaller the catalyst particle size, the larger the surface area for a given mass of particles. A heterogeneous catalyst has active sites, which are the atoms or crystal faces where the reaction actually occurs. Depending on the mechanism, the active site may be either a planar exposed metal surface, a crystal edge with imperfect metal valence or a complicated combination of the two. Thus, not only most of the volume, but also most of the surface of a heterogeneous catalyst may be catalytically inactive. Finding out the nature of the active site requires technically challenging research. Thus, empirical research for finding out new metal combinations for catalysis continues. For example, in the
Haber process The Haber process, also called the Haber–Bosch process, is an artificial nitrogen fixation process and is the main industrial procedure for the ammonia production, production of ammonia today. It is named after its inventors, the German chemists ...

Haber process
, finely divided
iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundance ...

iron
serves as a catalyst for the synthesis of
ammonia Ammonia is a chemical compound, compound of nitrogen and hydrogen with the chemical formula, formula NH3. A Binary compounds of hydrogen, stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct p ...
from
nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele and Henry Cavendish had independentl ...

nitrogen
and
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
. The reacting
gas Gas is one of the four fundamental states of matter (the others being solid, liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an appl ...

gas
es
adsorb of multilayer adsorption is a random distribution of molecules on the material surface. Adsorption is the adhesion Adhesion is the tendency of dissimilar Particle, particles or interface (matter), surfaces to cling to one another (Cohesion ...
onto active sites on the iron particles. Once physically adsorbed, the reagents undergo
chemisorptionChemisorption is a kind of adsorption of multilayer adsorption is a random distribution of molecules on the material surface. Adsorption is the adhesion Adhesion is the tendency of dissimilar Particle, particles or interface (matter), surfac ...
that results in dissociation into adsorbed atomic species, and new bonds between the resulting fragments form in part due to their close proximity. In this way the particularly strong
triple bond A triple bond in chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds compos ...

triple bond
in nitrogen is broken, which would be extremely uncommon in the gas phase due to its high activation energy. Thus, the activation energy of the overall reaction is lowered, and the rate of reaction increases. Another place where a heterogeneous catalyst is applied is in the oxidation of sulfur dioxide on
vanadium(V) oxide Vanadium(V) oxide (''vanadia'') is the inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition ...

vanadium(V) oxide
for the production of
sulfuric acid Sulfuric acid (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography English orthograp ...

sulfuric acid
. Heterogeneous catalysts are typically " supported," which means that the catalyst is dispersed on a second material that enhances the effectiveness or minimizes their cost. Supports prevent or reduce agglomeration and sintering small catalyst particles, exposing more surface area, thus catalysts have a higher specific activity (per gram) on a support. Sometimes the support is merely a surface on which the catalyst is spread to increase the surface area. More often, the support and the catalyst interact, affecting the catalytic reaction. Supports can also be used in nanoparticle synthesis by providing sites for individual molecules of catalyst to chemically bind. Supports are porous materials with a high surface area, most commonly
alumina Aluminium oxide is a chemical compound of aluminium and oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic ta ...
,
zeolites Zeolites are microporous, aluminosilicate mineral In geology Geology (from the Ancient Greek γῆ, ''gē'' ("earth") and -λoγία, ''-logia'', ("study of", "discourse")) is an Earth science concerned with the solid Earth, the rock (g ...
or various kinds of
activated carbon Activated carbon, also called activated charcoal, is a form of carbon Carbon (from la, carbo "coal") is a chemical element with the Symbol (chemistry), symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—making f ...

activated carbon
. Specialized supports include
silicon dioxide Silicon dioxide, also known as silica, is an oxide of rutile. Ti(IV) centers are grey; oxygen centers are red. Notice that oxygen forms three bonds to titanium and titanium forms six bonds to oxygen. An oxide () is a chemical compound that con ...
,
titanium dioxide Titanium dioxide, also known as titanium(IV) oxide or titania , is the inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compoun ...
,
calcium carbonate Calcium carbonate is a chemical compound with the formula Ca CO3. It is a common substance found in rocks as the minerals calcite and aragonite (most notably as limestone Limestone is a common type of carbonate rock, carbonate sediment ...

calcium carbonate
, and
barium sulfate Barium sulfate (or sulphate) is the inorganic compound In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules and ions: their composition, st ...
. In slurry reactions, heterogeneous catalysts can be lost by dissolving. Many heterogeneous catalysts are in fact nanomaterials. Nanomaterial-based catalysts with enzyme-mimicking activities are collectively called as nanozymes.


Electrocatalysts

In the context of
electrochemistry Electrochemistry is the branch of physical chemistry Physical chemistry is the study of macroscopic The macroscopic scale is the length scale on which objects or phenomena are large enough to be visible with the naked eye, without magnifying ...
, specifically in
fuel cell A fuel cell is an electrochemical cell An electrochemical cell is a device capable of either generating electrical energy from chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of ...

fuel cell
engineering, various metal-containing catalysts are used to enhance the rates of the
half reaction A half reaction is either the oxidation or reduction reaction component of a redox reaction. A half reaction is obtained by considering the change in oxidation states of individual substances involved in the redox reaction. Often, the concept of hal ...
s that comprise the fuel cell. One common type of fuel cell electrocatalyst is based upon
nanoparticles A nanoparticle or ultrafine particle is usually defined as a particle of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched ...

nanoparticles
of
platinum Platinum is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

platinum
that are supported on slightly larger
carbon Carbon (from la, carbo "coal") is a chemical element with the Symbol (chemistry), symbol C and atomic number 6. It is nonmetallic and tetravalence, tetravalent—making four electrons available to form covalent bond, covalent chemical bonds. ...
particles. When in contact with one of the
electrodes An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor A semiconductor material has an Electrical resistivity and conductivity, electrical conductivity value falling between tha ...
in a fuel cell, this platinum increases the rate of
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
reduction either to water, or to
hydroxide Hydroxide is a polyatomic ion, diatomic anion with chemical formula OH−. It consists of an oxygen and hydrogen atom held together by a single covalent bond, and carries a negative electric charge. It is an important but usually Self-ionization o ...
or
hydrogen peroxide Hydrogen peroxide is a chemical compound with the formula . In its pure form, it is a very pale blue liquid, slightly more viscosity, viscous than Properties of water, water. It is used as an oxidizer, bleaching agent, and antiseptic, usually as ...

hydrogen peroxide
.


Homogeneous catalysis

Homogeneous catalysts function in the same phase as the reactants. Typically homogeneous catalysts are dissolved in a solvent with the substrates. One example of homogeneous catalysis involves the influence of on the
esterification An ester is a chemical compound derived from an acid (organic or inorganic) in which at least one –OH hydroxyl group is replaced by an –O– alkyl ( alkoxy) group, as in the substitution reaction of a carboxylic acid and an alcohol. Glycer ...

esterification
of carboxylic acids, such as the formation of
methyl acetate Methyl acetate, also known as MeOAc, acetic acid methyl ester or methyl ethanoate, is a carboxylate ester An ester is a chemical compound derived from an acid (organic or inorganic) in which at least one –OH hydroxyl group is replaced by an ...

methyl acetate
from
acetic acid Acetic acid , systematically named ethanoic acid , is an acidic, colourless liquid and organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, ...

acetic acid
and
methanol Methanol, also known as methyl alcohol, amongst other names, is a Chemical compound, chemical and the simplest alcohol, with the Chemical formula, formula Carbon, CHydrogen, H3Oxygen, OHydrogen, H (a methyl group linked to a Hydroxy group, hydro ...

methanol
. High-volume processes requiring a homogeneous catalyst include
hydroformylation Hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehyde Chemically, an aldehyde is a compound containing a functional group with the structure −CHO, consisting of a carbonyl cente ...

hydroformylation
,
hydrosilylationHydrosilylation, also called catalytic hydrosilation, describes the addition of Si-H bonds across unsaturated bonds."Hydrosilylation A Comprehensive Review on Recent Advances" B. Marciniec (ed.), Advances in Silicon Science, Springer Science, 2009. ...

hydrosilylation
,
hydrocyanation Hydrocyanation is the addition of hydrogen, H+ and cyanide, –CN to Substrate (chemistry), substrate. Usually the substrate is an alkene and the product is a nitrile. Hydrocyanation of unactivated alkenes Industrially, hydrocyanation is comm ...

hydrocyanation
. For inorganic chemists, homogeneous catalysis is often synonymous with organometallic catalysts. Many homogeneous catalysts are however not organometallic, illustrated by the use of cobalt salts that catalyze the oxidation of
p-xylene ''p''-Xylene ( ''para''-xylene) is an aromatic hydrocarbon Aromatic compounds are those chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of ...
to
terephthalic acid Terephthalic acid is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenatio ...

terephthalic acid
.


Organocatalysis

Whereas transition metals sometimes attract most of the attention in the study of catalysis, small organic molecules without metals can also exhibit catalytic properties, as is apparent from the fact that many
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates int ...

enzyme
s lack transition metals. Typically, organic catalysts require a higher loading (amount of catalyst per unit amount of reactant, expressed in mol%
amount of substance In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound, compounds composed of atoms, mo ...
) than transition metal(-ion)-based catalysts, but these catalysts are usually commercially available in bulk, helping to reduce costs. In the early 2000s, these organocatalysts were considered "new generation" and are competitive to traditional
metal A metal (from Ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts Electrical resistivity and conductivity, el ...

metal
(-ion)-containing catalysts. Organocatalysts are supposed to operate akin to metal-free enzymes utilizing, e.g., non-covalent interactions such as
hydrogen bonding A hydrogen bond (or H-bond) is a primarily Electrostatics, electrostatic force of attraction between a hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of ...
. The discipline organocatalysis is divided in the application of covalent (e.g.,
proline Proline (symbol Pro or P) is an organic acid classed as a proteinogenic amino acid Proteinogenic amino acids are amino acids that are incorporated biosynthetically into proteins during translation (biology), translation. The word "proteinogenic" ...

proline
, DMAP) and non-covalent (e.g.,
thiourea organocatalysis Within the area of organocatalysis's synthesis of oxamide from dicyan and water represents the ''first organocatalytic reaction'', with acetaldehyde further identified as the first discovered pure "organocatalyst", which act similarly to the then-na ...
) organocatalysts referring to the preferred catalyst-
substrate Substrate may refer to: Physical layers *Substrate (biology), the natural environment in which an organism lives, or the surface or medium on which an organism grows or is attached **Substrate (locomotion), the surface over which an organism loco ...
binding and interaction, respectively.


Photocatalysts

Photocatalysis is the phenomenon where the catalyst can receive light (such as visible light), be promoted to an excited state, and then undergo
intersystem crossingIntersystem crossing (ISC) is an isoenergetic radiationless process involving a transition between the two electronic states with different states spin multiplicity. Singlet and triplet states When an electron in a molecule with a singlet ground ...
with the starting material, returning to ground state without being consumed. The excited state of the starting material will then undergo reactions it ordinarily could not if directly illuminated. For example,
singlet oxygen Singlet oxygen, systematically named dioxygen(singlet) and dioxidene, is a gaseous inorganic chemical with the formula O=O (also written as or ), which is in a quantum state where all electrons are spin paired. It is kinetically unstable at ambie ...
is usually produced by photocatalysis. Photocatalysts are also the main ingredient in
dye-sensitized solar cell A dye-sensitized solar cell (DSSC, DSC, DYSC or Grätzel cell) is a low-cost solar cell belonging to the group of thin film solar cells. It is based on a semiconductor formed between a photo-sensitized anode and an electrolyte, a ''Photoelectroc ...
s.


Enzymes and biocatalysts

In biology,
enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates int ...

enzyme
s are protein-based catalysts in
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main purposes of metabolism are: the conversion of the energy in food to energy available to run cellu ...

metabolism
and
catabolism Catabolism () is the set of metabolic Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities that have biological processes, such as s ...
. Most biocatalysts are enzymes, but other non-protein-based classes of biomolecules also exhibit catalytic properties including
ribozyme Ribozymes (ribonucleic acid enzymes) are RNA molecules that have the ability to catalyze specific biochemical reactions, including RNA splicing in gene expression, similar to the action of protein enzymes. The 1982 discovery of ribozymes demonst ...

ribozyme
s, and synthetic deoxyribozymes. Biocatalysts can be thought of as intermediate between homogeneous and heterogeneous catalysts, although strictly speaking soluble enzymes are homogeneous catalysts and
membrane Image:Schematic size.jpg, up150px, Schematic of size-based membrane exclusion A membrane is a selective barrier; it allows some things to pass through but stops others. Such things may be molecules, ions, or other small particles. Biological membr ...
-bound enzymes are heterogeneous. Several factors affect the activity of enzymes (and other catalysts) including temperature, pH, concentration of enzyme, substrate, and products. A particularly important reagent in enzymatic reactions is water, which is the product of many bond-forming reactions and a reactant in many bond-breaking processes. In
biocatalysis Biocatalysis refers to the use of living (biological) systems or their parts to speed up ( catalyze) chemical reactions. In biocatalytic processes, natural catalysts, such as enzyme Enzymes () are proteins that act as biological catalysts (bi ...
, enzymes are employed to prepare many commodity chemicals including
high-fructose corn syrup High-fructose corn syrup (HFCS), also known as glucose-fructose, isoglucose and glucose-fructose syrup, is a sweetener made from corn starch. As in the production of conventional corn syrup, the starch is broken down into glucose by enzymes. ...
and
acrylamide Acrylamide (or acrylic amide) is an organic compound with the chemical formula CH2=CHC(O)NH2. It is a white odorless solid, soluble in water (molecule), water and several organic solvents. It is produced industrially as a precursor to polyacrylamid ...
. Some
monoclonal antibodies A monoclonal antibody (mAb or moAb) is an antibody An antibody (Ab), also known as an immunoglobulin (Ig), is a large, Y-shaped protein used by the immune system to identify and neutralize foreign objects such as pathogenic bacteria and Viral ...

monoclonal antibodies
whose binding target is a stable molecule which resembles the transition state of a chemical reaction can function as weak catalysts for that chemical reaction by lowering its activation energy. Such catalytic antibodies are sometimes called " abzymes".


Significance

Estimates are that 90% of all commercially produced chemical products involve catalysts at some stage in the process of their manufacture. In 2005, catalytic processes generated about $900 billion in products worldwide. Catalysis is so pervasive that subareas are not readily classified. Some areas of particular concentration are surveyed below.


Energy processing

Petroleum Petroleum (), also known as crude oil and oil, is a #Latent heat of vaporization, naturally occurring, yellowish-black liquid found in geological formations beneath the Earth, Earth's surface. It is commonly refined into various types of fuels. ...

Petroleum
refining makes intensive use of catalysis for
alkylation Alkylation is the transfer of an alkyl group from one molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five carbon rings. A molecule is an electrically ...

alkylation
,
catalytic cracking Fluid catalytic cracking (FCC) is one of the most important conversion processes used in petroleum refineries. It is widely used to convert the high-boiling point, high-molecular weight hydrocarbon fractions of petroleum crude oils into more valu ...
(breaking long-chain hydrocarbons into smaller pieces),
naphtha Naphtha ( or ) is a flammable liquid hydrocarbon mixture. Mixtures labelled ''naphtha'' have been produced from natural gas condensates, petroleum distillates, and the distillation of coal tar and peat. In different industries and regions ''na ...
reforming and
steam reforming Steam reforming or steam methane reforming is a method for producing syngas (hydrogen and carbon monoxide) by reaction of hydrocarbons with water. Commonly natural gas is the feedstock. The main purpose of this technology is hydrogen production. The ...
(conversion of
hydrocarbon In organic chemistry, a hydrocarbon is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's a ...
s into
synthesis gas Syngas, or synthetic gas, is a fuel gas mixture consisting primarily of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest el ...
). Even the exhaust from the burning of fossil fuels is treated via catalysis:
Catalytic converter A catalytic converter is an exhaust emission control device that reduces toxic gases and pollutants in exhaust gas from an internal combustion engine An internal combustion engine (ICE) is a heat engine in which the combustion of a fuel o ...
s, typically composed of
platinum Platinum is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

platinum
and
rhodium Rhodium is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same numb ...

rhodium
, break down some of the more harmful byproducts of automobile exhaust. :2 CO + 2 NO → 2 CO + N With regard to synthetic fuels, an old but still important process is the Fischer-Tropsch synthesis of hydrocarbons from
synthesis gas Syngas, or synthetic gas, is a fuel gas mixture consisting primarily of hydrogen Hydrogen is the chemical element with the Symbol (chemistry), symbol H and atomic number 1. With a standard atomic weight of , hydrogen is the lightest el ...
, which itself is processed via , catalysed by iron.
Biodiesel Biodiesel is a form of diesel fuel Diesel fuel in general is any liquid fuel specifically designed for use in diesel engine The diesel engine, named after Rudolf Diesel, is an internal combustion engine An internal combustion e ...

Biodiesel
and related biofuels require processing via both inorganic and biocatalysts.
Fuel cell A fuel cell is an electrochemical cell An electrochemical cell is a device capable of either generating electrical energy from chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of ...

Fuel cell
s rely on catalysts for both the anodic and cathodic reactions.
Catalytic heaterA catalytic heater is a flameless heater which relies on catalyzed chemical reactions to break down molecule File:Pentacene on Ni(111) STM.jpg, A scanning tunneling microscopy image of pentacene molecules, which consist of linear chains of five ...
s generate flameless heat from a supply of combustible fuel.


Bulk chemicals

Some of the largest-scale chemicals are produced via catalytic oxidation, often using
oxygen Oxygen is the chemical element with the chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen Group (periodic table), group in the periodic table, a highly Chemical reaction, reactive nonmetal, and an oxidizing a ...

oxygen
. Examples include
nitric acid Nitric acid (), also known as ''aqua fortis'' (Latin for "strong water") and spirit of niter, is a highly corrosive mineral acid. The pure compound is colorless, but older samples tend to acquire a yellow cast due to decomposition into nitrogen ...

nitric acid
(from ammonia),
sulfuric acid Sulfuric acid (American spelling Despite the various English dialects spoken from country to country and within different regions of the same country, there are only slight regional variations in English orthography English orthograp ...

sulfuric acid
(from
sulfur dioxide Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a Toxicity, toxic gas responsible for the smell of burnt matches. It is released naturally by vol ...
to
sulfur trioxide Sulfur trioxide (alternative spelling sulphur trioxide) is the chemical compound with the formula SO3. It has been described as "unquestionably the most important economically" sulfur oxide. It is prepared on an industrial scale as a precursor to s ...
by the ),
terephthalic acid Terephthalic acid is an organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical bond, bonds. Due to carbon's ability to Catenatio ...

terephthalic acid
from p-xylene,
acrylic acid Acrylic acid (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science ...
from
propylene Propene, also known as propylene or methyl ethylene, is an unsaturated organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical ...

propylene
or
propane Propane () is a three- carbon alkane with the molecular formula . It is a gas at standard temperature and pressure, but compressible to a transportable liquid. A by-product of natural gas Natural gas (also called fossil gas; sometimes ju ...

propane
and
acrylonitrile Acrylonitrile is an organic compound with the formula CH2CHCN. It is a colorless volatile liquid although commercial samples can be yellow due to impurities. It has a pungent odor of garlic or onions. In terms of its molecular structure, it cons ...
from propane and ammonia. The production of ammonia is one of the largest-scale and most energy-intensive processes. In the
Haber process The Haber process, also called the Haber–Bosch process, is an artificial nitrogen fixation process and is the main industrial procedure for the ammonia production, production of ammonia today. It is named after its inventors, the German chemists ...

Haber process
nitrogen Nitrogen is the chemical element with the Symbol (chemistry), symbol N and atomic number 7. It was first discovered and isolated by Scottish physician Daniel Rutherford in 1772. Although Carl Wilhelm Scheele and Henry Cavendish had independentl ...

nitrogen
is combined with hydrogen over an iron oxide catalyst.
Methanol Methanol, also known as methyl alcohol, amongst other names, is a Chemical compound, chemical and the simplest alcohol, with the Chemical formula, formula Carbon, CHydrogen, H3Oxygen, OHydrogen, H (a methyl group linked to a Hydroxy group, hydro ...

Methanol
is prepared from
carbon monoxide Carbon monoxide (chemical formula CO) is a colorless, odorless, tasteless, flammable gas that is slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom. It is the simplest molecule of the oxocarbon family. In ...
or carbon dioxide but using copper-zinc catalysts. Bulk polymers derived from
ethylene Ethylene (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science Co ...

ethylene
and
propylene Propene, also known as propylene or methyl ethylene, is an unsaturated organic compound , CH4; is among the simplest organic compounds. In chemistry, organic compounds are generally any chemical compounds that contain carbon-hydrogen chemical ...

propylene
are often prepared via Ziegler-Natta catalysis. Polyesters, polyamides, and
isocyanate Isocyanate is the functional group with the formula R−N=C=O. Organic compounds that contain an isocyanate group are referred to as isocyanates. An organic compound with two isocyanate groups is known as a diisocyanate. Diisocyanates are manufa ...
s are derived via acid-base catalysis. Most carbonylation processes require metal catalysts, examples include the Monsanto acetic acid process and
hydroformylation Hydroformylation, also known as oxo synthesis or oxo process, is an industrial process for the production of aldehyde Chemically, an aldehyde is a compound containing a functional group with the structure −CHO, consisting of a carbonyl cente ...

hydroformylation
.


Fine chemicals

Many fine chemicals are prepared via catalysis; methods include those of heavy industry as well as more specialized processes that would be prohibitively expensive on a large scale. Examples include the Heck reaction, and Friedel–Crafts reactions. Because most bioactive compounds are Chirality (chemistry), chiral, many pharmaceuticals are produced by enantioselective catalysis (catalytic asymmetric synthesis).(R)-1,2-Propandiol, precursor to the antibacterial levofloxacin, can be efficiently synthesized from hydroxyacetone using Noyori asymmetric hydrogenation:


Food processing

One of the most obvious applications of catalysis is the hydrogenation (reaction with
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
gas) of fats using nickel catalyst to produce margarine. Many other foodstuffs are prepared via biocatalysis (see below).


Environment

Catalysis impacts the environment by increasing the efficiency of industrial processes, but catalysis also plays a direct role in the environment. A notable example is the catalytic role of chlorine free radicals in the breakdown of ozone. These radicals are formed by the action of ultraviolet radiation on chlorofluorocarbons (CFCs). :Cl + O → ClO + O :ClO + O → Cl + O


History

Generally speaking, anything that increases the rate of a process is a "catalyst", a term derived from Greek language, Greek wikt:καταλύω, καταλύειν, meaning "to annul," or "to untie," or "to pick up." The concept of catalysis was invented by chemist Elizabeth Fulhame and described in a 1794 book, based on her novel work in oxidation-reduction experiments. The first chemical reaction in organic chemistry that utilized a catalyst was studied in 1811 by Gottlieb Kirchhoff who discovered the acid-catalyzed conversion of starch to glucose. The term ''catalysis'' was later used by Jöns Jakob Berzelius in 1835 to describe reactions that are accelerated by substances that remain unchanged after the reaction. Elizabeth Fulhame, Fulhame, who predated Berzelius, did work with water as opposed to metals in her reduction experiments. Other 18th century chemists who worked in catalysis were Eilhard Mitscherlich who referred to it as ''contact'' processes, and Johann Wolfgang Döbereiner who spoke of ''contact action. ''He developed Döbereiner's lamp, a Lighter (fire starter), lighter based on
hydrogen Hydrogen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

hydrogen
and a
platinum Platinum is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

platinum
sponge, which became a commercial success in the 1820s that lives on today. Humphry Davy discovered the use of platinum in catalysis. In the 1880s, Wilhelm Ostwald at Leipzig University started a systematic investigation into reactions that were catalyzed by the presence of acids and bases, and found that chemical reactions occur at finite rates and that these rates can be used to determine the strengths of acids and bases. For this work, Ostwald was awarded the 1909 Nobel Prize in Chemistry. Vladimir Ipatieff performed some of the earliest industrial scale reactions, including the discovery and commercialization of oligomerization and the development of catalysts for hydrogenation.


Inhibitors, poisons, and promoters

An added substance which does reduce the reaction rate is a reaction inhibitor if reversible and Catalyst poisoning, catalyst poisons if irreversible. Promoters are substances that increase the catalytic activity, even though they are not catalysts by themselves. Inhibitors are sometimes referred to as "negative catalysts" since they decrease the reaction rate. However the term inhibitor is preferred since they do not work by introducing a reaction path with higher activation energy; this would not reduce the rate since the reaction would continue to occur by the non-catalyzed path. Instead they act either by deactivating catalysts, or by removing reaction intermediates such as free radicals.Laidler, K.J. (1978) ''Physical Chemistry with Biological Applications'', Benjamin/Cummings. pp. 415–17. .Laidler, K.J. and Meiser, J.H. (1982) ''Physical Chemistry'', Benjamin/Cummings, p. 425. . In heterogeneous catalysis, coking inhibits the catalyst, which becomes covered by polymeric side products. The inhibitor may modify selectivity in addition to rate. For instance, in the reduction of alkynes to alkenes, a palladium (Pd) catalyst partly "poisoned" with lead(II) acetate (Pb(CHCO)) can be used. Without the deactivation of the catalyst, the alkene produced would be further reduced to alkane.Bender, Myron L; Komiyama, Makoto and Bergeron, Raymond J (1984) ''The Bioorganic Chemistry of Enzymatic Catalysis'' Wiley-Interscience, Hoboken, U.S. The inhibitor can produce this effect by, e.g., selectively poisoning only certain types of active sites. Another mechanism is the modification of surface geometry. For instance, in hydrogenation operations, large planes of metal surface function as sites of hydrogenolysis catalysis while sites catalyzing hydrogenation of unsaturates are smaller. Thus, a poison that covers surface randomly will tend to reduce the number of uncontaminated large planes but leave proportionally more smaller sites free, thus changing the hydrogenation vs. hydrogenolysis selectivity. Many other mechanisms are also possible. Promoters can cover up surface to prevent production of a mat of coke, or even actively remove such material (e.g., rhenium on platinum in catalytic reforming, platforming). They can aid the dispersion of the catalytic material or bind to reagents.


See also

* Chemical reaction ** Substrate (chemistry), Substrate ** Reagent **
Enzyme Enzymes () are proteins that act as biological catalysts (biocatalysts). Catalysts accelerate chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates int ...

Enzyme
** Product (chemistry), Product * Abzyme * Acid catalysis (includes Base catalysis) * Autocatalysis * BIG-NSE (Berlin Graduate School of Natural Sciences and Engineering) * ''Catalysis Science & Technology'' (a chemistry journal) * Catalytic resonance theory * Electrocatalyst * Environmental triggers * Enzyme catalysis * Industrial catalysts * Kelvin probe force microscope * Limiting reagent * Pharmaceutic adjuvant * Phase-boundary catalysis * Phase transfer catalyst * Photocatalysis * Ribozyme (RNA biocatalyst) * SUMO enzymes * Temperature-programmed reduction * Thermal desorption spectroscopy


References

*


External links


Science Aid: Catalysts
Page for high school level science
W.A. Herrmann Technische Universität presentation

Alumite Catalyst, Kameyama-Sakurai Laboratory, Japan

Inorganic Chemistry and Catalysis Group, Utrecht University, The Netherlands



Carbons & Catalysts Group, University of Concepcion, Chile

Center for Enabling New Technologies Through Catalysis, An NSF Center for Chemical Innovation, USA

"Bubbles turn on chemical catalysts"
Science News magazine online, April 6, 2009. {{Authority control Catalysis, Chemical kinetics Articles containing video clips