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Catalysis

From Wikipedia, the free encyclopedia
"Catalyst" redirects here. For other uses, seeCatalyst (disambiguation).
Not to be confused withCatalistorCathalistis.
For the stage of metabolism, seecatabolism.

A range of industrial catalysts in pellet form
Anair filterthat uses a low-temperature oxidation catalyst to convertcarbon monoxideto less toxiccarbon dioxideat room temperature. It can also removeformaldehydefrom the air.

Catalysis(/kəˈtæləsɪs/) is the increase inrateof achemical reactiondue to an added substance known as acatalyst[1][2](/ˈkætəlɪst/). Catalysts are not consumed by the reaction and remain unchanged after it.[3]If the reaction is rapid and the catalyst recycles quickly, very small amounts of catalyst often suffice;[4]mi xing, surface area, and temperature are important factors in reaction rate. Catalysts generally react with one or more reactants to formintermediatesthat subsequently give 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.[5]

Catalysis may be classified as eitherhomogeneous,whose components are dispersed in the same phase (usually gaseous or liquid) as the reactant, orheterogeneous,whose components are not in the same phase.Enzymesand other biocatalysts are often considered as a third category.

Catalysis is ubiquitous inchemical industryof all kinds.[6]Estimates are that 90% of all commercially produced chemical products involve catalysts at some stage in the process of their manufacture.

The term "catalyst" is derived fromGreekκαταλύειν,kataluein,meaning "loosen" or "untie". The concept of catalysis was invented by chemistElizabeth Fulhame,based on her novel work in oxidation-reduction experiments.[7][8]

General principles

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Example

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An illustrative example is the effect of catalysts to speed the decomposition ofhydrogen peroxideinto water andoxygen:

2 H2O2→ 2 H2O + O2

This reaction proceeds because the reaction products are more stable than the starting compound, but this decomposition is so slow that hydrogen peroxide solutions are commercially available. In the presence of a catalyst such asmanganese dioxidethis reaction proceeds much more rapidly. This effect is readily seen by theeffervescenceof oxygen.[9]The catalyst is not consumed in the reaction, and may be recovered unchanged and re-used indefinitely. Accordingly, manganese dioxide is said tocatalyzethis reaction. In living organisms, this reaction is catalyzed byenzymes(proteins that serve as catalysts) such ascatalase.

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.[10]

Units

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TheSI derived unitfor measuring thecatalytic activityof a catalyst is thekatal,which is quantified in moles per second. The productivity of a catalyst can be described by theturnover number(or TON) and the catalytic activity by theturn over frequency(TOF), which is the TON per time unit. The biochemical equivalent is theenzyme unit.For more information on the efficiency of enzymatic catalysis, see the article onenzymes.

Catalytic reaction mechanisms

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Main article:catalytic cycle

In general, chemical reactions occur faster in the presence of a catalyst because the catalyst provides an alternativereaction mechanism(reaction pathway) having a loweractivation energythan the non-catalyzed mechanism. In catalyzed mechanisms, the catalyst is regenerated.[11][12][13][14]

As a simple example occurring in the gas phase, the reaction 2 SO2+ O2→ 2 SO3can be catalyzed by addingnitric oxide.The reaction occurs in two steps:

2NO + O2→ 2NO2(rate-determining)
NO2+ SO2→ NO + SO3(fast)

The NO catalyst is regenerated. The overall rate is the rate of the slow step[14]

v = 2k1[NO]2[O2].

An example ofheterogeneous catalysisis the reaction ofoxygenandhydrogenon the surface oftitanium dioxide(TiO2,ortitania) to produce water.Scanning tunneling microscopyshowed that the molecules undergoadsorptionanddissociation.The dissociated, surface-bound O and H atomsdiffusetogether. The intermediate reaction states are: HO2,H2O2,then H3O2and the reaction product (water molecule dimers), after which the water moleculedesorbsfrom the catalyst surface.[15][16]

Reaction energetics

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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 lower activation energy. The final result and the overall thermodynamics are the same.

Catalysts enable pathways that differ from the uncatalyzed reactions. These pathways have loweractivation energy.Consequently, more molecular collisions have the energy needed to reach thetransition state.Hence, catalysts can enable reactions that would otherwise be blocked or slowed by 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 anenergy profilediagram.

In the catalyzedelementary reaction,catalysts donotchange the extent of a reaction: they havenoeffect on thechemical equilibriumof a reaction. The ratio of the forward and the reverse reaction rates is unaffected (see alsothermodynamics). Thesecond law of thermodynamicsdescribes 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 ifGibbs free energyis 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 aperpetual motion machine,a contradiction to the laws of thermodynamics.[17]Thus, catalystsdo notalter 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-catalyzedhydrolysisofesters,where the producedcarboxylic acidimmediately 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 thedifferencein energy between starting material and the transition state. Itdoes notchange the energy difference between starting materials and products (thermodynamic barrier), or the available energy (this is provided by the environment as heat or light).

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Some so-called catalysts are reallyprecatalysts.Precatalysts convert to catalysts in the reaction. For example,Wilkinson's catalystRhCl(PPh3)3loses one triphenylphosphine ligand before entering the true catalytic cycle. Precatalysts are easier to store but are easily activatedin situ.Because of this preactivation step, many catalytic reactions involve aninduction period.

Incooperative catalysis,chemical species that improve catalytic activity are calledcocatalystsorpromoters.

Intandem catalysistwo or more different catalysts are coupled in a one-pot reaction.

Inautocatalysis,the catalystisa 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 anestersuch asaspirinto acarboxylic acidand analcohol.In the absence of added acid catalysts, the carboxylic acid product catalyzes the hydrolysis.

Switchable catalysisrefers to a type of catalysis where the catalyst can be toggled between different ground states possessing distinct reactivity, typically by applying an external stimulus.[18]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,[19]electric fields, or the addition of chemical agents.

A true catalyst can work in tandem with asacrificial 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(OsO4) is a good reagent for dihydroxylation, but it is highly toxic and expensive. InUpjohn dihydroxylation,the sacrificial catalystN-methylmorpholine N-oxide(NMMO) regenerates OsO4,and only catalytic quantities of OsO4are needed.

Classification

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Catalysis may be classified as eitherhomogeneous or heterogeneous.Ahomogeneous catalysisis one whose components are dispersed in the same phase (usually gaseous or liquid) as thereactant's molecules. Aheterogeneous catalysisis one where the reaction components are not in the same phase.Enzymesand other biocatalysts are often considered as a third category. Similar mechanistic principles apply to heterogeneous, homogeneous, and biocatalysis.

Heterogeneous catalysis

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Main article:Heterogeneous catalysis
The microporous molecular structure of thezeoliteZSM-5 is exploited in catalysts used in refineries
Zeolites are extruded as pellets for easy handling in catalytic reactors.

Heterogeneous catalysts act in a differentphasethan thereactants.Most heterogeneous catalysts aresolidsthat act on substrates in aliquidor gaseousreaction mixture.Important heterogeneous catalysts includezeolites,alumina,[20]higher-order oxides, graphitic carbon,transition metaloxides,metals such asRaney nickelfor hydrogenation, andvanadium(V) oxidefor oxidation ofsulfur dioxideintosulfur trioxideby thecontact process.[21]

Diverse mechanisms forreactions on surfacesare known, depending on how the adsorption takes place (Langmuir-Hinshelwood,Eley-Rideal,and Mars-van Krevelen).[22]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 hasactive sites,which are the atoms or crystal faces where the substrate actually binds. Active sites are atoms but are often described as 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 theHaber processfor the synthesis ofammoniafromnitrogenandhydrogenis often described asiron.But detailed studies and many optimizations have led to catalysts that are mixtures of iron-potassium-calcium-aluminum-oxide.[23]The reactinggasesadsorbonto active sites on the iron particles. Once physically adsorbed, the reagents partially or wholly dissociate and form new bonds. In this way the particularly strongtriple bondin 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.[24]Another place where a heterogeneous catalyst is applied is in the oxidation of sulfur dioxide onvanadium(V) oxidefor the production ofsulfuric acid.[21]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 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 a high surface area, most commonlyalumina,zeolitesor various kinds ofactivated carbon.Specialized supports includesilicon dioxide,titanium dioxide,calcium carbonate,andbarium sulfate.[25]

Electrocatalysts

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Main article:Electrocatalyst

In the context ofelectrochemistry,specifically infuel cellengineering, various metal-containing catalysts are used to enhance the rates of thehalf reactionsthat comprise the fuel cell. One common type of fuel cell electrocatalyst is based uponnanoparticlesofplatinumthat are supported on slightly largercarbonparticles. When in contact with one of theelectrodesin a fuel cell, this platinum increases the rate ofoxygenreduction either to water or tohydroxideorhydrogen peroxide.

Homogeneous catalysis

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Main article: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 ofH+on theesterificationof carboxylic acids, such as the formation ofmethyl acetatefromacetic acidandmethanol.[26]High-volume processes requiring a homogeneous catalyst includehydroformylation,hydrosilylation,hydrocyanation.For inorganic chemists, homogeneous catalysis is often synonymous withorganometallic catalysts.[27]Many homogeneous catalysts are however not organometallic, illustrated by the use of cobalt salts that catalyze the oxidation ofp-xylenetoterephthalic acid.

Organocatalysis

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Main article: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 manyenzymeslack transition metals. Typically, organic catalysts require a higher loading (amount of catalyst per unit amount of reactant, expressed inmol%amount of substance) than transition metal(-ion)-based catalysts, but these catalysts are usually commercially available in bulk, helping to lower costs. In the early 2000s, these organocatalysts were considered "new generation" and are competitive to traditionalmetal(-ion)-containing catalysts. Organocatalysts are supposed to operate akin to metal-free enzymes utilizing, e.g., non-covalent interactions such ashydrogen 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 the preferred catalyst-substratebindingand 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."[28]

Photocatalysts

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Main article:Photocatalysis

Photocatalysis is the phenomenon where the catalyst can receive light to generate anexcited statethat effect redox reactions.[29]Singlet oxygenis usually produced by photocatalysis. Photocatalysts are components ofdye-sensitized solar cells.

Enzymes and biocatalysts

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Main article:Enzyme catalysis

In biology,enzymesare protein-based catalysts inmetabolismandcatabolism.Most biocatalysts are enzymes, but other non-protein-based classes of biomolecules also exhibit catalytic properties includingribozymes,and syntheticdeoxyribozymes.[30]

Biocatalysts can be thought of as an intermediate between homogeneous and heterogeneous catalysts, although strictly speaking soluble enzymes are homogeneous catalysts andmembrane-bound enzymes are heterogeneous. Several factors affect 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.

Inbiocatalysis,enzymes are employed to prepare many commodity chemicals includinghigh-fructose corn syrupandacrylamide.

Somemonoclonal antibodieswhose binding target 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.[31]Such catalytic antibodies are sometimes called "abzymes".

Significance

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Left: Partially caramelizedcube sugar,Right: burning cube sugar with ash as catalyst
A Ti-Cr-Pt tube (~40 μm long) releases oxygen bubbles when immersed inhydrogen peroxide(via catalytic decomposition), forming amicropump.[32]

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.[33]Catalysis is so pervasive that subareas are not readily classified. Some areas of particular concentration are surveyed below.

Energy processing

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Petroleumrefining makes intensive use of catalysis foralkylation,catalytic cracking(breaking long-chain hydrocarbons into smaller pieces),naphthareforming andsteam reforming(conversion ofhydrocarbonsintosynthesis gas). Even the exhaust from the burning of fossil fuels is treated via catalysis:Catalytic converters,typically composed ofplatinumandrhodium,break down some of the more harmful byproducts of automobile exhaust.

2 CO + 2 NO → 2 CO2+ N2

With regard to synthetic fuels, an old but still important process is theFischer-Tropsch synthesisof hydrocarbons fromsynthesis gas,which itself is processed viawater-gas shift reactions,catalyzed by iron. TheSabatier reactionproducesmethanefrom carbon dioxide and hydrogen.Biodieseland related biofuels require processing via both inorganic and biocatalysts.

Fuel cellsrely on catalysts for both the anodic and cathodic reactions.

Catalytic heatersgenerate flameless heat from a supply of combustible fuel.

Bulk chemicals

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Typical vanadium pentoxide catalyst used in sulfuric acid production for an intermediate reaction to convert sulfur dioxide to sulfur trioxide.
Typical vanadium pentoxide catalyst used in sulfuric acid production for an intermediate reaction to convert sulfur dioxide to sulfur trioxide.

Some of the largest-scale chemicals are produced via catalytic oxidation, often usingoxygen.Examples includenitric acid(from ammonia),sulfuric acid(fromsulfur dioxidetosulfur trioxideby thecontact process),terephthalic acidfrom p-xylene,acrylic acidfrompropyleneorpropaneandacrylonitrilefrom propane and ammonia.[22]

The production of ammonia is one of the largest-scale and most energy-intensive processes. In theHaber processnitrogenis combined with hydrogen over an iron oxide catalyst.[34]Methanolis prepared fromcarbon monoxideor carbon dioxide but using copper-zinc catalysts.

Bulk polymers derived fromethyleneandpropyleneare often prepared viaZiegler-Natta catalysis.Polyesters, polyamides, andisocyanatesare derived viaacid-base catalysis.

Mostcarbonylationprocesses require metal catalysts, examples include theMonsanto acetic acid processandhydroformylation.

Fine chemicals

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Manyfine chemicalsare 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 theHeck reaction,andFriedel–Crafts reactions.Because most bioactive compounds arechiral,many pharmaceuticals are produced by enantioselective catalysis (catalyticasymmetric synthesis). (R)-1,2-Propandiol, the precursor to the antibacteriallevofloxacin,can be synthesized efficiently from hydroxyacetone by using catalysts based onBINAP-ruthenium complexes, inNoyori asymmetric hydrogenation:[35]

levofloxaxin synthesis
levofloxaxin synthesis

Food processing

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One of the most obvious applications of catalysis is thehydrogenation(reaction withhydrogengas) of fats usingnickelcatalyst to producemargarine.[36]Many other foodstuffs are prepared via biocatalysis (see below).

Environment

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Catalysis affects 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 ofchlorinefree radicalsin the breakdown ofozone.These radicals are formed by the action ofultravioletradiationonchlorofluorocarbons(CFCs).

Cl·+ O3→ ClO·+ O2
ClO·+ O·→ Cl·+ O2

History

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The term "catalyst", broadly defined as anything that increases the rate of a process, is derived fromGreekκαταλύειν,meaning "to annul," or "to untie," or "to pick up". The concept of catalysis was invented by chemistElizabeth Fulhameand described in a 1794 book, based on her novel work in oxidation–reduction reactions.[7][8][37]The first chemical reaction in organic chemistry that knowingly used a catalyst was studied in 1811 byGottlieb Kirchhoff,who discovered the acid-catalyzed conversion of starch to glucose. The termcatalysiswas later used byJöns Jakob Berzeliusin 1835[38]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 wereEilhard Mitscherlich[39]who referred to it ascontactprocesses, andJohann Wolfgang Döbereiner[40][41]who spoke ofcontact action.He developedDöbereiner's lamp,alighterbased onhydrogenand aplatinumsponge, which became a commercial success in the 1820s that lives on today.Humphry Davydiscovered the use of platinum in catalysis.[42]In the 1880s,Wilhelm OstwaldatLeipzig Universitystarted 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 1909Nobel Prize in Chemistry.[43]Vladimir Ipatieffperformed some of the earliest industrial scale reactions, including the discovery and commercialization of oligomerization and the development of catalysts for hydrogenation.[44]

Inhibitors, poisons, and promoters

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An added substance that lowers the rate is called areaction inhibitorif reversible andcatalyst poisonsif irreversible.[1]Promoters are substances that increase the catalytic activity, even though they are not catalysts by themselves.[45]

Inhibitors are sometimes referred to as "negative catalysts" since they decrease the reaction rate.[46]However the term inhibitor is preferred since they do not work by introducing a reaction path with higher activation energy; this would not lower 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.[46][11]Inheterogeneouscatalysis,cokinginhibits the catalyst, which becomes covered bypolymericside products.

The inhibitor may modify selectivity in addition to rate. For instance, in the hydrogenation ofalkynestoalkenes,apalladium(Pd) catalyst partly "poisoned" withlead(II) acetate(Pb(CH3CO2)2) can be used (Lindlar catalyst).[47]Without the deactivation of the catalyst, the alkene produced would be further hydrogenated toalkane.[48][49]

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 ofhydrogenolysiscatalysis while sites catalyzinghydrogenationof unsaturates are smaller. Thus, a poison that covers the surface randomly will tend to lower the number of uncontaminated large planes but leave proportionally smaller sites free, thus changing the hydrogenation vs. hydrogenolysis selectivity. Many other mechanisms are also possible.

Promoters can cover up the surface to prevent the production of a mat of coke, or even actively remove such material (e.g., rhenium on platinum inplatforming). They can aid the dispersion of the catalytic material or bind to reagents.

See also

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References

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  36. ^Clark, Jim (October 2013)."Types of catalysis".Chemguide.
  37. ^Bård Lindström and Lars J. Petterson (2003) "A brief history of catalysis"Cattech,7(4): 130–38.
  38. ^Berzelius, J.J. (1835)Årsberättelsen om framsteg i fysik och kemi[Annual report on progress in physics and chemistry]. Stockholm, Sweden: Royal Swedish Academy of Sciences. After reviewing Eilhard Mitscherlich's research on the formation of ether, Berzelius coins the wordkatalys(catalysis) onp. 245:

    Original:Jag skall derföre, för att begagna en i kemien välkänd härledning, kalla den kropparskatalytiska kraft,sönderdelning genom denna kraftkatalys,likasom vi med ordet analys beteckna åtskiljandet af kroppars beståndsdelar medelst den vanliga kemiska frändskapen.

    Translation:I shall, therefore, to employ a well-known derivation in chemistry, call [the catalytic] bodies [i.e., substances] thecatalytic forceand the decomposition of [other] bodies by this forcecatalysis,just as we signify by the wordanalysisthe separation of the constituents of bodies by the usual chemical affinities.
  39. ^Mitscherlich, E. (1834)."Ueber die Aetherbildung"[On the formation of ether].Annalen der Physik und Chemie.31(18): 273–82.Bibcode:1834AnP...107..273M.doi:10.1002/andp.18341071802.
  40. ^Döbereiner (1822)."Glühendes Verbrennen des Alkohols durch verschiedene erhitzte Metalle und Metalloxyde"[Incandescent burning of alcohol by various heated metals and metal oxides].Journal für Chemie und Physik.34:91–92.
  41. ^Döbereiner (1823)."Neu entdeckte merkwürdige Eigenschaften des Platinsuboxyds, des oxydirten Schwefel-Platins und des metallischen Platinstaubes"[Newly discovered remarkable properties of platinum suboxide, oxidized platinum sulfide and metallic platinum dust].Journal für Chemie und Physik.38:321–26.
  42. ^Davy, Humphry (1817)."Some new experiments and observations on the combustion of gaseous mixtures, with an account of a method of preserving a continued light in mixtures of inflammable gases and air without flame".Philosophical Transactions of the Royal Society of London.107:77–85.doi:10.1098/rstl.1817.0009.S2CID97988261.
  43. ^Roberts, M.W. (2000). "Birth of the catalytic concept (1800–1900)".Catalysis Letters.67(1): 1–4.doi:10.1023/A:1016622806065.S2CID91507819.
  44. ^Nicholas, Christopher P. (August 21, 2018)."Dehydration, Dienes, High Octane, and High Pressures: Contributions from Vladimir Nikolaevich Ipatieff, a Father of Catalysis".ACS Catalysis.8(9): 8531–39.doi:10.1021/acscatal.8b02310.
  45. ^Dhara SS; Umare SS (2018).A Textbook of Engineering Chemistry.India: S. Chand Publishing. p. 66.ISBN9789352830688.
  46. ^abLaidler, K.J. (1978)Physical Chemistry with Biological Applications,Benjamin/Cummings. pp. 415–17.ISBN0-8053-5680-0.
  47. ^Lindlar H.; Dubuis R. (2016). "Palladium Catalyst for Partial Reduction of Acetylenes".Organic Syntheses.doi:10.15227/orgsyn.046.0089;Collected Volumes,vol. 5, p. 880.
  48. ^Jencks, W.P. (1969)Catalysis in Chemistry and EnzymologyMcGraw-Hill, New York.ISBN0-07-032305-4
  49. ^Bender, Myron L; Komiyama, Makoto and Bergeron, Raymond J (1984)The Bioorganic Chemistry of Enzymatic CatalysisWiley-Interscience, Hoboken, U.S.ISBN0-471-05991-9
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