107-545: Catalysis ( / k ə ˈ t æ l ə s ɪ s / ) is the increase in rate of a chemical reaction due to an added substance known as a catalyst ( / ˈ k æ t əl ɪ s t / ). Catalysts are not consumed by the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice; mixing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to form intermediates that subsequently give
214-572: A cascade method, Swiss chemist and physicist Raoul Pierre Pictet evaporated liquid sulfur dioxide in order to liquefy carbon dioxide, which in turn was evaporated to cool oxygen gas enough to liquefy it. He sent a telegram on December 22, 1877, to the French Academy of Sciences in Paris announcing his discovery of liquid oxygen . Just two days later, French physicist Louis Paul Cailletet announced his own method of liquefying molecular oxygen. Only
321-448: A lighter based on hydrogen and a 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
428-407: A liquid or gaseous reaction mixture . Important heterogeneous catalysts include zeolites , alumina , higher-order oxides, graphitic carbon, transition metal oxides , metals such as Raney nickel for hydrogenation, and vanadium(V) oxide for oxidation of sulfur dioxide into sulfur trioxide by the contact process . Diverse mechanisms for reactions on surfaces are known, depending on how
535-477: A chemical element. The name oxygen was coined in 1777 by Antoine Lavoisier , who first recognized oxygen as a chemical element and correctly characterized the role it plays in combustion. Common industrial uses of oxygen include production of steel , plastics and textiles , brazing, welding and cutting of steels and other metals , rocket propellant , oxygen therapy , and life support systems in aircraft , submarines , spaceflight and diving . One of
642-593: A facet (edge, surface, step, etc.) of a solid. 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 is technically challenging. For example, the catalyst for the Haber process for the synthesis of ammonia from nitrogen and hydrogen is often described as iron . But detailed studies and many optimizations have led to catalysts that are mixtures of iron-potassium-calcium-aluminum-oxide. The reacting gases adsorb onto active sites on
749-434: A few drops of the liquid were produced in each case and no meaningful analysis could be conducted. Oxygen was liquefied in a stable state for the first time on March 29, 1883, by Polish scientists from Jagiellonian University , Zygmunt Wróblewski and Karol Olszewski . In 1891 Scottish chemist James Dewar was able to produce enough liquid oxygen for study. The first commercially viable process for producing liquid oxygen
856-451: A high surface area, most commonly alumina , zeolites or various kinds of activated carbon . Specialized supports include silicon dioxide , titanium dioxide , calcium carbonate , and barium sulfate . In the context of electrochemistry , specifically in fuel cell engineering, various metal-containing catalysts are used to enhance the rates of the half reactions that comprise the fuel cell. One common type of fuel cell electrocatalyst
963-401: A higher specific activity (per gram) on 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
1070-406: A kinetic barrier. The catalyst may increase the reaction rate or selectivity, or enable the reaction at lower temperatures. This effect can be illustrated with an energy profile diagram. In the catalyzed elementary reaction , catalysts do not change the extent of a reaction: they have no effect on the chemical equilibrium of a reaction. The ratio of the forward and the reverse reaction rates
1177-481: A light sky-blue color caused by absorption in the red (in contrast with the blue color of the sky, which is due to Rayleigh scattering of blue light). High-purity liquid O 2 is usually obtained by the fractional distillation of liquefied air. Liquid oxygen may also be condensed from air using liquid nitrogen as a coolant. Liquid oxygen is a highly reactive substance and must be segregated from combustible materials. The spectroscopy of molecular oxygen
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#17328695161301284-560: A major role in absorbing energy from singlet oxygen and converting it to the unexcited ground state before it can cause harm to tissues. The common allotrope of elemental oxygen on Earth is called dioxygen , O 2 , the major part of the Earth's atmospheric oxygen (see Occurrence ). O 2 has a bond length of 121 pm and a bond energy of 498 kJ/mol . O 2 is used by complex forms of life, such as animals, in cellular respiration . Other aspects of O 2 are covered in
1391-409: A one-pot reaction. In autocatalysis , 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
1498-438: A part of air that he called spiritus nitroaereus . In one experiment, he found that placing either a mouse or a lit candle in a closed container over water caused the water to rise and replace one-fourteenth of the air's volume before extinguishing the subjects. From this, he surmised that nitroaereus is consumed in both respiration and combustion. Mayow observed that antimony increased in weight when heated, and inferred that
1605-404: A process called eutrophication and the decay of these organisms and other biomaterials may reduce the O 2 content in eutrophic water bodies. Scientists assess this aspect of water quality by measuring the water's biochemical oxygen demand , or the amount of O 2 needed to restore it to a normal concentration. Paleoclimatologists measure the ratio of oxygen-18 and oxygen-16 in
1712-468: A process, is derived from Greek 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 reactions. The first chemical reaction in organic chemistry that knowingly used a catalyst was studied in 1811 by Gottlieb Kirchhoff , who discovered the acid-catalyzed conversion of starch to glucose. The term catalysis
1819-458: A small proportion of manganese dioxide. Oxygen levels in the atmosphere are trending slightly downward globally, possibly because of fossil-fuel burning. At standard temperature and pressure , oxygen is a colorless, odorless, and tasteless gas with the molecular formula O 2 , referred to as dioxygen. As dioxygen , two oxygen atoms are chemically bound to each other. The bond can be variously described based on level of theory, but
1926-449: A triplet electronic ground state . An electron configuration with two unpaired electrons, as is found in dioxygen orbitals (see the filled π* orbitals in the diagram) that are of equal energy—i.e., degenerate —is a configuration termed a spin triplet state. Hence, the ground state of the O 2 molecule is referred to as triplet oxygen . The highest-energy, partially filled orbitals are antibonding , and so their filling weakens
2033-399: A type of catalysis where the catalyst can be toggled between different ground states possessing distinct reactivity, typically by applying an external stimulus. This ability to reversibly switch the catalyst allows for spatiotemporal control over catalytic activity and selectivity. The external stimuli used to switch the catalyst can include changes in temperature, pH, light, electric fields, or
2140-576: Is the most abundant element in Earth's crust , and the third-most abundant element in the universe after hydrogen and helium . At standard temperature and pressure , two oxygen atoms will bind covalently to form dioxygen , a colorless and odorless diatomic gas with the chemical formula O 2 . Dioxygen gas currently constitutes 20.95% molar fraction of the Earth's atmosphere , though this has changed considerably over long periods of time in Earth's history . Oxygen makes up almost half of
2247-570: Is a corrosive byproduct of smog and thus an air pollutant . Oxygen was isolated by Michael Sendivogius before 1604, but it is commonly believed that the element was discovered independently by Carl Wilhelm Scheele , in Uppsala , in 1773 or earlier, and Joseph Priestley in Wiltshire , in 1774. Priority is often given for Priestley because his work was published first. Priestley, however, called oxygen "dephlogisticated air", and did not recognize it as
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#17328695161302354-427: Is a good reagent for dihydroxylation, but it is highly toxic and expensive. In Upjohn dihydroxylation , the sacrificial catalyst N-methylmorpholine N-oxide (NMMO) regenerates OsO 4 , and only catalytic quantities of OsO 4 are needed. Catalysis may be classified as either homogeneous or heterogeneous . A homogeneous catalysis is one whose components are dispersed in the same phase (usually gaseous or liquid) as
2461-464: Is a stable molecule that 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 ". 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
2568-477: Is absorbed by specialized respiratory organs called gills , through the skin or via the gut ; in terrestrial animals such as tetrapods , oxygen in air is actively taken into the body via specialized organs known as lungs , where gas exchange takes place to diffuse oxygen into the blood and carbon dioxide out, and the body's circulatory system then transports the oxygen to other tissues where cellular respiration takes place. However in insects ,
2675-475: Is applied is in the oxidation of sulfur dioxide on vanadium(V) oxide for the production of sulfuric acid . Many heterogeneous catalysts are in fact nanomaterials. Heterogeneous catalysts are typically " supported ", which means that the catalyst is dispersed on a second material that enhances the effectiveness or minimizes its cost. Supports prevent or minimize agglomeration and sintering of small catalyst particles, exposing more surface area, thus catalysts have
2782-508: Is associated with the atmospheric processes of aurora and airglow . The absorption in the Herzberg continuum and Schumann–Runge bands in the ultraviolet produces atomic oxygen that is important in the chemistry of the middle atmosphere. Excited-state singlet molecular oxygen is responsible for red chemiluminescence in solution. Table of thermal and physical properties of oxygen (O 2 ) at atmospheric pressure: Naturally occurring oxygen
2889-408: Is based upon nanoparticles of platinum that are supported on slightly larger carbon particles. When in contact with one of the electrodes in a fuel cell, this platinum increases the rate of oxygen reduction either to water or to hydroxide or hydrogen peroxide . Homogeneous catalysts function in the same phase as the reactants. Typically homogeneous catalysts are dissolved in a solvent with
2996-469: Is composed of three stable isotopes , O , O , and O , with O being the most abundant (99.762% natural abundance ). Most O is synthesized at the end of the helium fusion process in massive stars but some is made in the neon burning process . O is primarily made by the burning of hydrogen into helium during the CNO cycle , making it a common isotope in the hydrogen burning zones of stars. Most O
3103-415: Is derived from Greek καταλύειν , kataluein , meaning "loosen" or "untie". The concept of catalysis was invented by chemist Elizabeth Fulhame , based on her novel work in oxidation-reduction experiments. An illustrative example is the effect of catalysts to speed the decomposition of hydrogen peroxide into water and oxygen : This reaction proceeds because the reaction products are more stable than
3210-512: Is one of the largest-scale and most energy-intensive processes. In the Haber process nitrogen is combined with hydrogen over an iron oxide catalyst. Methanol is prepared from carbon monoxide or carbon dioxide but using copper-zinc catalysts. Bulk polymers derived from ethylene and propylene are often prepared via Ziegler-Natta catalysis . Polyesters, polyamides, and isocyanates are derived via acid-base catalysis . Most carbonylation processes require metal catalysts, examples include
3317-447: Is oxygen as a component of water, the major constituent of lifeforms. Oxygen in Earth's atmosphere is produced by biotic photosynthesis , in which photon energy in sunlight is captured by chlorophyll to split water molecules and then react with carbon dioxide to produce carbohydrates and oxygen is released as a byproduct . Oxygen is too chemically reactive to remain a free element in air without being continuously replenished by
Catalysis - Misplaced Pages Continue
3424-441: Is produced when N (made abundant from CNO burning) captures a He nucleus, making O common in the helium-rich zones of evolved, massive stars . Fifteen radioisotopes have been characterized, ranging from O to O. The most stable are O with a half-life of 122.24 seconds and O with a half-life of 70.606 seconds. All of the remaining radioactive isotopes have half-lives that are less than 27 seconds and
3531-406: Is produced, and if there is no energy barrier, there is no need for a catalyst. Then, removing the catalyst would also result in a 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 , a contradiction to the laws of thermodynamics. Thus, catalysts do not alter
3638-408: Is reasonably and simply described as a covalent double bond that results from the filling of molecular orbitals formed from the atomic orbitals of the individual oxygen atoms, the filling of which results in a bond order of two. More specifically, the double bond is the result of sequential, low-to-high energy, or Aufbau , filling of orbitals, and the resulting cancellation of contributions from
3745-474: Is regenerated. The overall rate is the rate of the slow step An example of heterogeneous catalysis is the reaction of oxygen and hydrogen on the surface of titanium dioxide (TiO 2 , or titania ) to produce water. Scanning tunneling microscopy showed that the molecules undergo adsorption and dissociation . The dissociated, surface-bound O and H atoms diffuse together. The intermediate reaction states are: HO 2 , H 2 O 2 , then H 3 O 2 and
3852-571: Is said to catalyze this reaction. In living organisms, this reaction is catalyzed by enzymes (proteins that serve as catalysts) such as catalase . Another example is the effect of catalysts on air pollution and reducing the amount of carbon monoxide. Development of active and selective catalysts for the conversion of carbon monoxide into desirable products is one of the most important roles of catalysts. Using catalysts for hydrogenation of carbon monoxide helps to remove this toxic gas and also attain useful materials. The SI derived unit for measuring
3959-412: Is so pervasive that subareas are not readily classified. Some areas of particular concentration are surveyed below. Petroleum refining makes intensive use of catalysis for alkylation , catalytic cracking (breaking long-chain hydrocarbons into smaller pieces), naphtha reforming and steam reforming (conversion of hydrocarbons into synthesis gas ). Even the exhaust from the burning of fossil fuels
4066-712: Is temperature-dependent, and about twice as much ( 14.6 mg/L ) dissolves at 0 °C than at 20 °C ( 7.6 mg/L ). At 25 °C and 1 standard atmosphere (101.3 kPa ) of air, freshwater can dissolve about 6.04 milliliters (mL) of oxygen per liter , and seawater contains about 4.95 mL per liter. At 5 °C the solubility increases to 9.0 mL (50% more than at 25 °C) per liter for freshwater and 7.2 mL (45% more) per liter for sea water. Oxygen condenses at 90.20 K (−182.95 °C, −297.31 °F) and freezes at 54.36 K (−218.79 °C, −361.82 °F). Both liquid and solid O 2 are clear substances with
4173-435: Is the result of the oxygen cycle . This biogeochemical cycle describes the movement of oxygen within and between its three main reservoirs on Earth: the atmosphere, the biosphere, and the lithosphere . The main driving factor of the oxygen cycle is photosynthesis , which is responsible for modern Earth's atmosphere. Photosynthesis releases oxygen into the atmosphere, while respiration , decay , and combustion remove it from
4280-652: Is treated via catalysis: Catalytic converters , typically composed of platinum and rhodium , break down some of the more harmful byproducts of automobile exhaust. With regard to synthetic fuels, an old but still important process is the Fischer-Tropsch synthesis of hydrocarbons from synthesis gas , which itself is processed via water-gas shift reactions , catalyzed by iron. The Sabatier reaction produces methane from carbon dioxide and hydrogen. Biodiesel and related biofuels require processing via both inorganic and biocatalysts. Fuel cells rely on catalysts for both
4387-439: Is unaffected (see also thermodynamics ). The second law of thermodynamics 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
Catalysis - Misplaced Pages Continue
4494-457: Is unusual among the planets of the Solar System in having such a high concentration of oxygen gas in its atmosphere: Mars (with 0.1% O 2 by volume) and Venus have much less. The O 2 surrounding those planets is produced solely by the action of ultraviolet radiation on oxygen-containing molecules such as carbon dioxide. The unusually high concentration of oxygen gas on Earth
4601-517: Is usually given priority in the discovery. The French chemist Antoine Laurent Lavoisier later claimed to have discovered the new substance independently. Priestley visited Lavoisier in October 1774 and told him about his experiment and how he liberated the new gas. Scheele had also dispatched a letter to Lavoisier on September 30, 1774, which described his discovery of the previously unknown substance, but Lavoisier never acknowledged receiving it (a copy of
4708-608: The Earth , the Moon , Mars , and meteorites , but were long unable to obtain reference values for the isotope ratios in the Sun , believed to be the same as those of the primordial solar nebula . Analysis of a silicon wafer exposed to the solar wind in space and returned by the crashed Genesis spacecraft has shown that the Sun has a higher proportion of oxygen-16 than does the Earth. The measurement implies that an unknown process depleted oxygen-16 from
4815-463: The Earth's crust in the form of various oxides such as water , carbon dioxide , iron oxides and silicates . All eukaryotic organisms , including plants , animals , fungi , algae and most protists , need oxygen for cellular respiration , which extracts chemical energy by the reaction of oxygen with organic molecules derived from food and releases carbon dioxide as a waste product. In aquatic animals , dissolved oxygen in water
4922-556: The Greek roots ὀξύς (oxys) ( acid , literally 'sharp', from the taste of acids) and -γενής (-genēs) (producer, literally begetter), because he mistakenly believed that oxygen was a constituent of all acids. Chemists (such as Sir Humphry Davy in 1812) eventually determined that Lavoisier was wrong in this regard, but by then the name was too well established. Oxygen entered the English language despite opposition by English scientists and
5029-577: The Monsanto acetic acid process and hydroformylation . 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 chiral , many pharmaceuticals are produced by enantioselective catalysis (catalytic asymmetric synthesis ). (R)-1,2-Propandiol,
5136-511: The catalytic activity of a catalyst is the katal , which is quantified in moles per second. The productivity of a catalyst can be described by the turnover number (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 unit . For more information on the efficiency of enzymatic catalysis, see the article on enzymes . In general, chemical reactions occur faster in
5243-423: The reactant 's molecules. A heterogeneous catalysis is one where the reaction components are not in the same phase. Enzymes and other biocatalysts are often considered as a third category. Similar mechanistic principles apply to heterogeneous, homogeneous, and biocatalysis. Heterogeneous catalysts act in a different phase than the reactants . Most heterogeneous catalysts are solids that act on substrates in
5350-470: The shells and skeletons of marine organisms to determine the climate millions of years ago (see oxygen isotope ratio cycle ). Seawater molecules that contain the lighter isotope , oxygen-16, evaporate at a slightly faster rate than water molecules containing the 12% heavier oxygen-18, and this disparity increases at lower temperatures. During periods of lower global temperatures, snow and rain from that evaporated water tends to be higher in oxygen-16, and
5457-430: The thermal decomposition of potassium nitrate . In Bugaj's view, the isolation of oxygen and the proper association of the substance to that part of air which is required for life, provides sufficient evidence for the discovery of oxygen by Sendivogius. This discovery of Sendivogius was however frequently denied by the generations of scientists and chemists which succeeded him. It is also commonly claimed that oxygen
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#17328695161305564-553: The 17th and the 18th century but none of them recognized it as a chemical element . This may have been in part due to the prevalence of the philosophy of combustion and corrosion called the phlogiston theory , which was then the favored explanation of those processes. Established in 1667 by the German alchemist J. J. Becher , and modified by the chemist Georg Ernst Stahl by 1731, phlogiston theory stated that all combustible materials were made of two parts. One part, called phlogiston,
5671-531: The 2s electrons, after sequential filling of the low σ and σ orbitals; σ overlap of the two atomic 2p orbitals that lie along the O–O molecular axis and π overlap of two pairs of atomic 2p orbitals perpendicular to the O–O molecular axis, and then cancellation of contributions from the remaining two 2p electrons after their partial filling of the π orbitals. This combination of cancellations and σ and π overlaps results in dioxygen's double-bond character and reactivity, and
5778-527: The American scientist Robert H. Goddard became the first person to develop a rocket engine that burned liquid fuel; the engine used gasoline for fuel and liquid oxygen as the oxidizer . Goddard successfully flew a small liquid-fueled rocket 56 m at 97 km/h on March 16, 1926, in Auburn, Massachusetts , US. In academic laboratories, oxygen can be prepared by heating together potassium chlorate mixed with
5885-478: The Philosopher's Stone drawn from the source of nature and manual experience"] (1604) described a substance contained in air, referring to it as 'cibus vitae' (food of life, ) and according to Polish historian Roman Bugaj, this substance is identical with oxygen. Sendivogius, during his experiments performed between 1598 and 1604, properly recognized that the substance is equivalent to the gaseous byproduct released by
5992-438: The Sun's disk of protoplanetary material prior to the coalescence of dust grains that formed the Earth. Oxygen presents two spectrophotometric absorption bands peaking at the wavelengths 687 and 760 nm . Some remote sensing scientists have proposed using the measurement of the radiance coming from vegetation canopies in those bands to characterize plant health status from a satellite platform. This approach exploits
6099-478: The activity of enzymes (and other catalysts) including temperature, pH, the concentration of enzymes, 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 , enzymes are employed to prepare many commodity chemicals including high-fructose corn syrup and acrylamide . Some monoclonal antibodies whose binding target
6206-421: The addition of chemical agents. A true catalyst can work in tandem with a sacrificial catalyst . The true catalyst is consumed in the elementary reaction and turned into a deactivated form. The sacrificial catalyst regenerates the true catalyst for another cycle. The sacrificial catalyst is consumed in the reaction, and as such, it is not really a catalyst, but a reagent. For example, osmium tetroxide (OsO 4 )
6313-441: The adsorption takes place ( Langmuir-Hinshelwood , Eley-Rideal , and Mars- van Krevelen ). The total surface area of a 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 substrate actually binds. Active sites are atoms but are often described as
6420-501: The anodic and cathodic reactions. Catalytic heaters generate flameless heat from a supply of combustible fuel. Some of the largest-scale chemicals are produced via catalytic oxidation, often using oxygen . Examples include nitric acid (from ammonia), sulfuric acid (from sulfur dioxide to sulfur trioxide by the contact process ), terephthalic acid from p-xylene, acrylic acid from propylene or propane and acrylonitrile from propane and ammonia. The production of ammonia
6527-493: The atmosphere. In the present equilibrium, production and consumption occur at the same rate. Free oxygen also occurs in solution in the world's water bodies. The increased solubility of O 2 at lower temperatures (see Physical properties ) has important implications for ocean life, as polar oceans support a much higher density of life due to their higher oxygen content. Water polluted with plant nutrients such as nitrates or phosphates may stimulate growth of algae by
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#17328695161306634-412: The bond order from three to two. Because of its unpaired electrons, triplet oxygen reacts only slowly with most organic molecules, which have paired electron spins; this prevents spontaneous combustion. In the triplet form, O 2 molecules are paramagnetic . That is, they impart magnetic character to oxygen when it is in the presence of a magnetic field, because of the spin magnetic moments of
6741-507: The details below. Request from 172.68.168.226 via cp1108 cp1108, Varnish XID 821512353 Upstream caches: cp1108 int Error: 429, Too Many Requests at Fri, 29 Nov 2024 08:38:36 GMT Oxygen Oxygen is a chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table , a highly reactive nonmetal , and a potent oxidizing agent that readily forms oxides with most elements as well as with other compounds . Oxygen
6848-444: The diatomic elemental molecules in those gases. The first commercial method of producing oxygen was chemical, the so-called Brin process involving a reversible reaction of barium oxide . It was invented in 1852 and commercialized in 1884, but was displaced by newer methods in early 20th century. By the late 19th century scientists realized that air could be liquefied and its components isolated by compressing and cooling it. Using
6955-462: The early 2000s, these organocatalysts were considered "new generation" and are competitive to traditional metal (-ion)-containing catalysts. Organocatalysts are supposed to operate akin to metal-free enzymes utilizing, e.g., non-covalent interactions such as hydrogen bonding . The discipline organocatalysis is divided into the application of covalent (e.g., proline , DMAP ) and non-covalent (e.g., thiourea organocatalysis ) organocatalysts referring to
7062-466: The electron spins are paired. It is much more reactive with common organic molecules than is normal (triplet) molecular oxygen. In nature, singlet oxygen is commonly formed from water during photosynthesis, using the energy of sunlight. It is also produced in the troposphere by the photolysis of ozone by light of short wavelength and by the immune system as a source of active oxygen. Carotenoids in photosynthetic organisms (and possibly animals) play
7169-407: 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). The term "catalyst", broadly defined as anything that increases the rate of
7276-431: 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-catalyzed hydrolysis of esters , where the produced carboxylic acid immediately reacts with the base catalyst and thus the reaction equilibrium is shifted towards hydrolysis.) The catalyst stabilizes
7383-563: The fact that the Englishman Priestley had first isolated the gas and written about it. This is partly due to a poem praising the gas titled "Oxygen" in the popular book The Botanic Garden (1791) by Erasmus Darwin , grandfather of Charles Darwin . John Dalton 's original atomic hypothesis presumed that all elements were monatomic and that the atoms in compounds would normally have the simplest atomic ratios with respect to one another. For example, Dalton assumed that water's formula
7490-507: The final reaction product, in the process of regenerating the catalyst. The rate increase occurs because the catalyst allows the reaction to occur by an alternative mechanism which may be much faster than the non-catalyzed mechanism. However the non-catalyzed mechanism does remain possible, so that the total rate (catalyzed plus non-catalyzed) can only increase in the presence of the catalyst and never decrease. Catalysis may be classified as either homogeneous , whose components are dispersed in
7597-399: The first known experiments on the relationship between combustion and air was conducted by the 2nd century BCE Greek writer on mechanics, Philo of Byzantium . In his work Pneumatica , Philo observed that inverting a vessel over a burning candle and surrounding the vessel's neck with water resulted in some water rising into the neck. Philo incorrectly surmised that parts of the air in
7704-399: The idea; instead, it was based on observations of what happens when something burns, that most common objects appear to become lighter and seem to lose something in the process. Polish alchemist , philosopher , and physician Michael Sendivogius (Michał Sędziwój) in his work De Lapide Philosophorum Tractatus duodecim e naturae fonte et manuali experientia depromti ["Twelve Treatises on
7811-413: The iron particles. Once physically adsorbed, the reagents partially or wholly dissociate and form new bonds. In this way the particularly strong 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
7918-499: The letter was found in Scheele's belongings after his death). Lavoisier conducted the first adequate quantitative experiments on oxidation and gave the first correct explanation of how combustion works. He used these and similar experiments, all started in 1774, to discredit the phlogiston theory and to prove that the substance discovered by Priestley and Scheele was a chemical element . In one experiment, Lavoisier observed that there
8025-428: The majority of these have half-lives that are less than 83 milliseconds. The most common decay mode of the isotopes lighter than O is β decay to yield nitrogen, and the most common mode for the isotopes heavier than O is beta decay to yield fluorine . Oxygen is the most abundant chemical element by mass in the Earth's biosphere , air, sea and land. Oxygen is the third most abundant chemical element in
8132-418: The most successful and biodiverse terrestrial clade , oxygen is directly conducted to the internal tissues via a deep network of airways . Many major classes of organic molecules in living organisms contain oxygen atoms, such as proteins , nucleic acids , carbohydrates and fats , as do the major constituent inorganic compounds of animal shells, teeth, and bone. Most of the mass of living organisms
8239-494: The nitroaereus must have combined with it. He also thought that the lungs separate nitroaereus from air and pass it into the blood and that animal heat and muscle movement result from the reaction of nitroaereus with certain substances in the body. Accounts of these and other experiments and ideas were published in 1668 in his work Tractatus duo in the tract "De respiratione". Robert Hooke , Ole Borch , Mikhail Lomonosov , and Pierre Bayen all produced oxygen in experiments in
8346-451: The photosynthetic activities of autotrophs such as cyanobacteria , chloroplast -bearing algae and plants. A much rarer triatomic allotrope of oxygen , ozone ( O 3 ), strongly absorbs the UVB and UVC wavelengths and forms a protective ozone layer at the lower stratosphere , which shields the biosphere from ionizing ultraviolet radiation . However, ozone present at the surface
8453-491: The precursor to the antibacterial levofloxacin , can be synthesized efficiently from hydroxyacetone by using catalysts based on BINAP -ruthenium complexes, in Noyori asymmetric hydrogenation : One of the most obvious applications of catalysis is the hydrogenation (reaction with hydrogen gas) of fats using nickel catalyst to produce margarine . Many other foodstuffs are prepared via biocatalysis (see below). Catalysis affects
8560-1073: The preferred catalyst- substrate binding and interaction, respectively. The Nobel Prize in Chemistry 2021 was awarded jointly to Benjamin List and David W.C. MacMillan "for the development of asymmetric organocatalysis." Photocatalysis is the phenomenon where the catalyst can receive light to generate an excited state that effect redox reactions. Singlet oxygen is usually produced by photocatalysis. Photocatalysts are components of dye-sensitized solar cells . In biology, enzymes are protein-based catalysts in metabolism and catabolism . Most biocatalysts are enzymes, but other non-protein-based classes of biomolecules also exhibit catalytic properties including ribozymes , and synthetic deoxyribozymes . Biocatalysts can be thought of as an intermediate between homogeneous and heterogeneous catalysts, although strictly speaking soluble enzymes are homogeneous catalysts and membrane -bound enzymes are heterogeneous. Several factors affect
8667-424: The presence of a catalyst because the catalyst provides an alternative reaction mechanism (reaction pathway) having a lower activation energy than the non-catalyzed mechanism. In catalyzed mechanisms, the catalyst is regenerated. As a simple example occurring in the gas phase, the reaction 2 SO 2 + O 2 → 2 SO 3 can be catalyzed by adding nitric oxide . The reaction occurs in two steps: The NO catalyst
8774-413: The reaction product ( water molecule dimers ), after which the water molecule desorbs from the catalyst surface. Catalysts enable pathways that differ from the uncatalyzed reactions. These pathways have lower 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
8881-419: 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 such as aspirin to a carboxylic acid and an alcohol . In the absence of added acid catalysts, the carboxylic acid product catalyzes the hydrolysis. Switchable catalysis refers to
8988-499: The reaction. For example, Wilkinson's catalyst RhCl(PPh 3 ) 3 loses one triphenylphosphine ligand before entering the true catalytic cycle. Precatalysts are easier to store but are easily activated in situ . Because of this preactivation step, many catalytic reactions involve an induction period . In cooperative catalysis , chemical species that improve catalytic activity are called cocatalysts or promoters . In tandem catalysis two or more different catalysts are coupled in
9095-455: The remainder of this article. Trioxygen ( O 3 ) is usually known as ozone and is a very reactive allotrope of oxygen that is damaging to lung tissue. Ozone is produced in the upper atmosphere when O 2 combines with atomic oxygen made by the splitting of O 2 by ultraviolet (UV) radiation. Since ozone absorbs strongly in the UV region of the spectrum , the ozone layer of
9202-422: The same phase (usually gaseous or liquid) as the reactant, or heterogeneous , whose components are not in the same phase. Enzymes and other biocatalysts are often considered as a third category. Catalysis is ubiquitous in chemical industry of all kinds. Estimates are that 90% of all commercially produced chemical products involve catalysts at some stage in the process of their manufacture. The term "catalyst"
9309-414: The seawater left behind tends to be higher in oxygen-18. Marine organisms then incorporate more oxygen-18 into their skeletons and shells than they would in a warmer climate. Paleoclimatologists also directly measure this ratio in the water molecules of ice core samples as old as hundreds of thousands of years. Planetary geologists have measured the relative quantities of oxygen isotopes in samples from
9416-413: The starting compound, but this decomposition is so slow that hydrogen peroxide solutions are commercially available. In the presence of a catalyst such as manganese dioxide this reaction proceeds much more rapidly. This effect is readily seen by the effervescence of oxygen. The catalyst is not consumed in the reaction, and may be recovered unchanged and re-used indefinitely. Accordingly, manganese dioxide
9523-500: 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. Reaction rate Too Many Requests If you report this error to the Wikimedia System Administrators, please include
9630-497: The substrates. One example of homogeneous catalysis involves the influence of H on the esterification of carboxylic acids, such as the formation of methyl acetate from acetic acid and methanol . High-volume processes requiring a homogeneous catalyst include hydroformylation , hydrosilylation , hydrocyanation . For inorganic chemists, homogeneous catalysis is often synonymous with organometallic catalysts . Many homogeneous catalysts are however not organometallic, illustrated by
9737-474: 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 the 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). Some so-called catalysts are really precatalysts . Precatalysts convert to catalysts in
9844-486: The universe, after hydrogen and helium. About 0.9% of the Sun 's mass is oxygen. Oxygen constitutes 49.2% of the Earth's crust by mass as part of oxide compounds such as silicon dioxide and is the most abundant element by mass in the Earth's crust . It is also the major component of the world's oceans (88.8% by mass). Oxygen gas is the second most common component of the Earth's atmosphere , taking up 20.8% of its volume and 23.1% of its mass (some 10 tonnes). Earth
9951-401: The unpaired electrons in the molecule, and the negative exchange energy between neighboring O 2 molecules. Liquid oxygen is so magnetic that, in laboratory demonstrations, a bridge of liquid oxygen may be supported against its own weight between the poles of a powerful magnet. Singlet oxygen is a name given to several higher-energy species of molecular O 2 in which all
10058-435: The upper atmosphere functions as a protective radiation shield for the planet. Near the Earth's surface, it is a pollutant formed as a by-product of automobile exhaust . At low earth orbit altitudes, sufficient atomic oxygen is present to cause corrosion of spacecraft . The metastable molecule tetraoxygen ( O 4 ) was discovered in 2001, and was assumed to exist in one of the six phases of solid oxygen . It
10165-617: The use of cobalt salts that catalyze the oxidation of p-xylene to terephthalic acid . 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 enzymes lack transition metals. Typically, organic catalysts require a higher loading (amount of catalyst per unit amount of reactant, expressed in mol% amount of substance ) than transition metal(-ion)-based catalysts, but these catalysts are usually commercially available in bulk, helping to lower costs. In
10272-451: The vessel were converted into the classical element fire and thus were able to escape through pores in the glass. Many centuries later Leonardo da Vinci built on Philo's work by observing that a portion of air is consumed during combustion and respiration . In the late 17th century, Robert Boyle proved that air is necessary for combustion. English chemist John Mayow (1641–1679) refined this work by showing that fire requires only
10379-428: Was HO, leading to the conclusion that the atomic mass of oxygen was 8 times that of hydrogen, instead of the modern value of about 16. In 1805, Joseph Louis Gay-Lussac and Alexander von Humboldt showed that water is formed of two volumes of hydrogen and one volume of oxygen; and by 1811 Amedeo Avogadro had arrived at the correct interpretation of water's composition, based on what is now called Avogadro's law and
10486-408: Was first discovered by Swedish pharmacist Carl Wilhelm Scheele . He had produced oxygen gas by heating mercuric oxide (HgO) and various nitrates in 1771–72. Scheele called the gas "fire air" because it was then the only known agent to support combustion. He wrote an account of this discovery in a manuscript titled Treatise on Air and Fire , which he sent to his publisher in 1775. That document
10593-451: Was given off when the substance containing it was burned, while the dephlogisticated part was thought to be its true form, or calx . Highly combustible materials that leave little residue , such as wood or coal, were thought to be made mostly of phlogiston; non-combustible substances that corrode, such as iron, contained very little. Air did not play a role in phlogiston theory, nor were any initial quantitative experiments conducted to test
10700-491: Was independently developed in 1895 by German engineer Carl von Linde and British engineer William Hampson . Both men lowered the temperature of air until it liquefied and then distilled the component gases by boiling them off one at a time and capturing them separately. Later, in 1901, oxyacetylene welding was demonstrated for the first time by burning a mixture of acetylene and compressed O 2 . This method of welding and cutting metal later became common. In 1923,
10807-474: Was later used by Jöns Jakob Berzelius in 1835 to describe reactions that are accelerated by substances that remain unchanged after the reaction. 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 ,
10914-445: Was no overall increase in weight when tin and air were heated in a closed container. He noted that air rushed in when he opened the container, which indicated that part of the trapped air had been consumed. He also noted that the tin had increased in weight and that increase was the same as the weight of the air that rushed back in. This and other experiments on combustion were documented in his book Sur la combustion en général , which
11021-462: Was not sensibly different from that of common air , but I fancied that my breast felt peculiarly light and easy for some time afterwards." Priestley published his findings in 1775 in a paper titled "An Account of Further Discoveries in Air", which was included in the second volume of his book titled Experiments and Observations on Different Kinds of Air . Because he published his findings first, Priestley
11128-408: Was proven in 2006 that this phase, created by pressurizing O 2 to 20 GPa , is in fact a rhombohedral O 8 cluster . This cluster has the potential to be a much more powerful oxidizer than either O 2 or O 3 and may therefore be used in rocket fuel . A metallic phase was discovered in 1990 when solid oxygen is subjected to a pressure of above 96 GPa and it
11235-499: Was published in 1777. In the meantime, on August 1, 1774, an experiment conducted by the British clergyman Joseph Priestley focused sunlight on mercuric oxide contained in a glass tube, which liberated a gas he named "dephlogisticated air". He noted that candles burned brighter in the gas and that a mouse was more active and lived longer while breathing it. After breathing the gas himself, Priestley wrote: "The feeling of it to my lungs
11342-458: Was published in 1777. In that work, he proved that air is a mixture of two gases; 'vital air', which is essential to combustion and respiration, and azote (Gk. ἄζωτον "lifeless"), which did not support either. Azote later became nitrogen in English, although it has kept the earlier name in French and several other European languages. Lavoisier renamed 'vital air' to oxygène in 1777 from
11449-420: Was shown in 1998 that at very low temperatures, this phase becomes superconducting . Oxygen dissolves more readily in water than nitrogen, and in freshwater more readily than in seawater. Water in equilibrium with air contains approximately 1 molecule of dissolved O 2 for every 2 molecules of N 2 (1:2), compared with an atmospheric ratio of approximately 1:4. The solubility of oxygen in water
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