Chapter 1 Intro to Catalysis

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Chapter 1Chapter 1

Introduction toIntroduction toCatalysisCatalysis

Chapter 1Chapter 1

Introduction toIntroduction toCatalysisCatalysis

Dr. Leong Loong KongDr. Leong Loong [email protected]@utar.edu.my

[email protected]@yahoo.com.sg


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Catalysis in IndustryCatalysis in Industry

Catalysts are the workhorses of chemicalCatalysts are the workhorses of chemicaltransformations in the industry.transformations in the industry. ~ 85 ~ 85 90%90% of theof the

products of chemical industry are made in catalyticproducts of chemical industry are made in catalyticprocesses. Catalysts are indispensable in:processes. Catalysts are indispensable in:

P roduction of transportation fuels in one of theP roduction of transportation fuels in one of the~ 440 oil refineries all over the world.~ 440 oil refineries all over the world.

P roduction of bulk and fine chemicals in allP roduction of bulk and fine chemicals in allbranches of chemical industry branches of chemical industry


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P revention of pollution by avoiding formation of P revention of pollution by avoiding formation of waste (unwanted byproducts) waste (unwanted byproducts)

Abatement of pollution in end Abatement of pollution in end--of of--pipe solutionspipe solutions(automotive and industrial exhaust)(automotive and industrial exhaust)

A catalyst offers an alternative, energetically A catalyst offers an alternative, energetically favorable mechanism to the non favorable mechanism to the non- -catalytic catalytic reaction, thus enabling processes to be carried out reaction, thus enabling processes to be carried out under industrially feasible conditions of pressure under industrially feasible conditions of pressure and temperature.and temperature.


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W hat is Catalysis? W hat is Catalysis?

A catalyst A catalyst alters the rate of a c hemi c al rea c ti on alters the rate of a c hemi c al rea c ti on ..

It does so by forming bonds with the reacting It does so by forming bonds with the reacting molecules, and by allowing these to react to amolecules, and by allowing these to react to aproduct, which detaches from the catalyst, andproduct, which detaches from the catalyst, andleaves it unaltered such that it is available for theleaves it unaltered such that it is available for thenext reaction.next reaction.


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Every catalytic reaction is a sequence of elementary steps,in which reactant molecules bind to the catalyst, where

they react, after which the product detaches from the

catalyst, liberating the latter for the next cycle.


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P otential energy diagram of a heterogeneous catalyticreaction, with gaseous reactants and products and a solidcatalyst.

Note that the uncatalyzed reaction has to overcome asubstantial energy barrier, whereas the barriers in thecatalytic route are much lower.


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Several important points:Several important points:

T he catalyst offers an alternative path for the The catalyst offers an alternative path for thereaction, which is obviously more complex, butreaction, which is obviously more complex, but

energetically much more favorable.energetically much more favorable.

T he a c tivati on e n ergy of the c atalyti c rea c ti on is T he a c tivati on e n ergy of the c atalyti c rea c ti on is

sig n i f i c a n tly smaller tha n that of the unc atalyzed rea c ti on sig n i f i c a n tly smaller tha n that of the unc atalyzed rea c ti on ; ; hence, the rate of the catalytic reaction is muchhence, the rate of the catalytic reaction is muchlarger.larger.


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T he overall change in free energy for the catalytic The overall change in free energy for the catalytic

reaction equals that of the uncatalyzed reaction. Hence,reaction equals that of the uncatalyzed reaction. Hence,the catalyst does not affect the equilibrium constant forthe catalyst does not affect the equilibrium constant forthe overall reaction of the overall reaction of A + B A + B toto PP ..

Thus, if a reaction is thermodynamically unfavorable, a Thus, if a reaction is thermodynamically unfavorable, acatalyst cannot change this situation. A catalyst changescatalyst cannot change this situation. A catalyst changesthe kinetics but not the thermodynamics.the kinetics but not the thermodynamics.

T he catalyst accelerates both the forward and the The catalyst accelerates both the forward and thereverse reaction to the same extent.reverse reaction to the same extent.In other words, if a catalyst accelerates the formation of In other words, if a catalyst accelerates the formation of the productthe product PP fromfrom A and B A and B , it will do the same for the, it will do the same for thedecomposition of decomposition of PP intointo A and B A and B ..


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Combination of catalyst with reactants or productsCombination of catalyst with reactants or products will not be successful: will not be successful:

1. If the bonding between reactants and catalyst is1. If the bonding between reactants and catalyst istoo weak, there will be hardly any conversion of Atoo weak, there will be hardly any conversion of A

and B into products.and B into products.

2. Conversely if the bond between the catalyst and2. Conversely if the bond between the catalyst andone of the reactants, say A, is too strong, theone of the reactants, say A, is too strong, thecatalyst will be mostly occupied with species A,catalyst will be mostly occupied with species A,and B is not available to form the product.and B is not available to form the product.


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If A and B both form strong bonds with theIf A and B both form strong bonds with thecatalyst, the intermediate situation with A or B oncatalyst, the intermediate situation with A or B onthe catalyst may be so stable that reaction becomesthe catalyst may be so stable that reaction becomesunlikely.unlikely. The second level lies so deep that the activation The second level lies so deep that the activation

energy to form P on the catalyst becomes tooenergy to form P on the catalyst becomes toohigh. The catalyst is said to be poisoned by (onehigh. The catalyst is said to be poisoned by (oneof) the reactants.of) the reactants.

3. In the same way, the product P may be too3. In the same way, the product P may be toostrongly bound to the catalyst for separation tostrongly bound to the catalyst for separation tooccur. In this case the product poisons theoccur. In this case the product poisons the

catalyst.catalyst.


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Activation Energy


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Catalysts Can Be A toms, Molecules, EnzymesCatalysts Can Be A toms, Molecules, Enzymesand Solid Surfacesand Solid Surfaces

V ary from atoms and molecules to large V ary from atoms and molecules to largestructures such as zeolites or enzymes.structures such as zeolites or enzymes.

May be employed in various surroundings:May be employed in various surroundings: i n i n liq u ids, gases or at the s u r f a c e of s olids liq u ids, gases or at the s u r f a c e of s olids ..

P reparing a catalyst in the optimum form andP reparing a catalyst in the optimum form andstudying its precise composition and shape arestudying its precise composition and shape arean important specialism.an important specialism.


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Cl + OCl + O 33 pp ClOClO33ClOClO33 pp ClO + OClO + O 22

ClO + OClO + O pp Cl + OCl + O 22or overallor overall

OO33+ O+ O pp OO22

Ozone can decompose spontaneously, and alsoOzone can decompose spontaneously, and alsounder the influence of light, but a Cl atomunder the influence of light, but a Cl atomaccelerates the reaction tremendously. As itaccelerates the reaction tremendously. As itleaves the reaction cycle unaltered, theleaves the reaction cycle unaltered, the Cl atom Cl atom is a catalyst is a catalyst ..


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Catalytic carbonylation of methanol to acetic acidCatalytic carbonylation of methanol to acetic acid

CHCH33OH + COOH + CO pp CHCH33COOHCOOH

Catalyst : [Rh(CO)Catalyst : [Rh(CO)22II22 ] ]

complexes in solutioncomplexes in solution


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2 . Biocatalysis2 . Biocatalysis

Enzymes are natures catalysts : A large proteinEnzymes are natures catalysts : A large protein

The structure of which results in The structure of which results in a very sha pe a very sha pe- -s pe c i f i c s pe c i f i c a c tive site a c tive site ..

Having shapes that are optimally suited to guideHaving shapes that are optimally suited to guidereactant molecules (usually referred to asreactant molecules (usually referred to assubstrates) in the optimum configuration forsubstrates) in the optimum configuration forreaction, enzymes are highly specific and efficientreaction, enzymes are highly specific and efficientcatalysts.catalysts.


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Enzyme catalase catalyzes the decomposition of hydrogen peroxide into water and oxygen

2H 2O 2 p H2O + O 2at an incredibly high rate of up to 10 7 hydrogenperoxide molecules per second


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Breakdown of alcohol to acetaldehyde inside theBreakdown of alcohol to acetaldehyde inside thebody by the enzyme alcohol dehydrogenase.body by the enzyme alcohol dehydrogenase.

The acetaldehyde in turn is converted into acetate The acetaldehyde in turn is converted into acetate

by aldehyde hydrogenase.by aldehyde hydrogenase.

Some people cannot tolerate alcohol (as revealedSome people cannot tolerate alcohol (as revealed

by facial flushing after drinking a small amount)by facial flushing after drinking a small amount)because they lack the form of the enzyme thatbecause they lack the form of the enzyme thatbreaks down acetaldehyde.breaks down acetaldehyde.


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Cl eaning of automotive exhaustCl eaning of automotive exhaustCatalytic oxidation of CO on the surface of noble

metals such as platinum, palladium and rhodium.


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W hy is Catalysis Important? W hy is Catalysis Important?

Reactions can in general be controlled on theReactions can in general be controlled on thebasis of basis of tem perat u re,conc e n trati on , press u re a n d con ta c t tem perat u re,conc e n trati on , press u re a n d con ta c t time time ..

Raising the temperature and pressure will enableRaising the temperature and pressure will enablestoichiometric reactions to proceed at astoichiometric reactions to proceed at a

reasonable rate of production, but the reactorsreasonable rate of production, but the reactorsin which such conditions can be safely in which such conditions can be safely maintained become progressively moremaintained become progressively moreexpensive and difficult to make.expensive and difficult to make.


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T here are thermodynamic limitations to the There are thermodynamic limitations to theconditions under which products can be formed,conditions under which products can be formed,e.g. the conversion of Ne.g. the conversion of N 22 and Hand H 22 into ammoniainto ammoniais practically impossible above 600is practically impossible above 600 C.C.

Nevertheless, higher temperatures are needed toNevertheless, higher temperatures are needed tobreak the very strong N N bond in Nbreak the very strong N N bond in N 22..

Without catalysts, many reactions that are Without catalysts, many reactions that arecommon in the chemical industry would not becommon in the chemical industry would not bepossible, and many other processes would notpossible, and many other processes would notbe economical.be economical.


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Catalysts accelerate reactions by orders of Catalysts accelerate reactions by orders of

magnitude, enabling them to be carried outmagnitude, enabling them to be carried outunder the most favorable thermodynamicunder the most favorable thermodynamicregime, and at much lower temperatures andregime, and at much lower temperatures and

pressures.pressures.

Efficient catalysts in combination withEfficient catalysts in combination withoptimized reactor and total plant design, are theoptimized reactor and total plant design, are thekey factor in reducing both the investment andkey factor in reducing both the investment andoperation costs of a chemical processes.operation costs of a chemical processes.


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Catalysis and Green ChemistryCatalysis and Green Chemistry

Technology is called green if it uses raw materials Technology is called green if it uses raw materialsefficiently, such that the use of toxic and hazardousefficiently, such that the use of toxic and hazardousreagents and solvents can be avoided while formation of reagents and solvents can be avoided while formation of

waste or undesirable by waste or undesirable by--products is minimized.products is minimized.

Example:Example:

Selective oxidation of ethylene to ethylene epoxide, anSelective oxidation of ethylene to ethylene epoxide, animportant intermediate towards ethylene glycolimportant intermediate towards ethylene glycol(antifreeze) and various polyethers and polyurethanes(antifreeze) and various polyethers and polyurethanes


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Ethylene epoxideEthylene epoxide , animportant intermediatein the chemicalindustry.

The old, non-catalytic route (called the epichlorohydrine process) follows a three-step synthesis:

Cl2 + NaOHp

HOCl + NaCl (1)C2H4 + HOCl p CH 2ClCH 2OH (epichlorohydrine) (2)CH 2ClCH 2OH + 1/2Ca(OH) 2

1/2CaCl 2 + C 2H 4O +H 2O (3)


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or in total:or in total:

ClCl22 + NaOH + 1/2Ca(OH)+ NaOH + 1/2Ca(OH) 22 + C+ C 22HH44q

CC22 HH 44OO + 1/2CaCl+ 1/2CaCl 22 + NaCl + H+ NaCl + H 22OO

Every molecule of ethylene oxide, 1 molecule of Every molecule of ethylene oxide, 1 molecule of salt is formed, creating a waste problem that wassalt is formed, creating a waste problem that wastraditionally solved by dumping it in a river.traditionally solved by dumping it in a river.


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Catalytic Route:Catalytic Route:

Simple and clean, although it does produce a smallSimple and clean, although it does produce a smallamount of COamount of CO 22..

Using silver, promoted by small amounts of Using silver, promoted by small amounts of chlorine, as the catalyst, ethylene oxide is formedchlorine, as the catalyst, ethylene oxide is formed

directly from Cdirectly from C22HH44 and Oand O 22 at a selectivity of at a selectivity of around 90 %, with about 10% of the ethylenearound 90 %, with about 10% of the ethyleneending up as COending up as CO 22..


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A tom Efficiency, E Factors and A tom Efficiency, E Factors andEnvironmental FriendlinessEnvironmental Friendliness

1.1. A t om Eff i c ie nc y A t om Eff i c ie nc y is the molecular weight of the desiredis the molecular weight of the desiredproduct divided by the total molecular weight of allproduct divided by the total molecular weight of allproducts.products.

Example:Example:Conventional oxidation of a secondary alcoholConventional oxidation of a secondary alcohol

3C3C66HH55 CHOHCHOH CHCH33 + 2CrO+ 2CrO 33 + 3H+ 3H 22SOSO44qq

3C3C66HH55 COCO CHCH33 + Cr+ Cr 22( SO( SO44 ) )33 + 6H+ 6H 22OO

has an atom efficiency of 360/860 = 42%.has an atom efficiency of 360/860 = 42%.


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By contrast, the catalytic routeBy contrast, the catalytic route

CC66HH55 CHOHCHOH CHCH33 + 1/2O+ 1/2O 22qq

CC66HH55 COCO CHCH33 + H+ H 22OO

offers an atom efficiency of 120/138 = 87%, withoffers an atom efficiency of 120/138 = 87%, with water as the only byproduct. water as the only byproduct.


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3 .3 . En vir on me n tal q uotie n t EQ as the E f a c t or En vir on me n tal q uotie n t EQ as the E f a c t or

multiplied by an unfriendliness quotient, Q, whichmultiplied by an unfriendliness quotient, Q, whichcan be assigned a value to indicate how can be assigned a value to indicate how undesirable a byproduct is.undesirable a byproduct is.

Q = 0 for clean waterQ = 0 for clean waterQ = 1 for a benign salt, NaClQ = 1 for a benign salt, NaCl

Q = 100Q = 100 1000 for toxic compounds1000 for toxic compounds


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Largest processes based on heterogeneous catalysisLargest processes based on heterogeneous catalysis


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Organic chemical production in the US A (200 1)Organic chemical production in the US A (200 1)along with average annual change over the ten yearsalong with average annual change over the ten years

19911991 200 1200 1


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Inorganic chemical production in the US A (200 1)Inorganic chemical production in the US A (200 1)along with average annual change over the ten yearsalong with average annual change over the ten years

19911991 200 1200 1


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Polymers and plastics produced in the US A (200 1)Polymers and plastics produced in the US A (200 1)along with average annual change over the ten yearsalong with average annual change over the ten years

19911991 200 1200 1


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W orld T op 5 0 of Chemical Producers (Source: W orld T op 5 0 of Chemical Producers (Source:Chemical & Engineering News, July 2 9, 2002 )Chemical & Engineering News, July 2 9, 2002 )


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Relevant length scales in catalysis range from thesubnanometre domain of the atomic and molecular level to

the macroscopic domain of an industrial reactor


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Significance of catalysisSignificance of catalysis1. En ergy pr oc essi n g 1. En ergy pr oc essi n g

P etroleumP etroleum refining makes intensive use of catalysis forrefining makes intensive use of catalysis for

alkylationalkylation,, catalytic cracking catalytic cracking (breaking long (breaking long--chainchainhydrocarbons into smaller pieces),hydrocarbons into smaller pieces), naphthanaphtha reforming andreforming andsteam reforming steam reforming (conversion of (conversion of hydrocarbonshydrocarbons intointosynthesis gassynthesis gas ). ).

Even the exhaust from the burning of fossil fuels isEven the exhaust from the burning of fossil fuels istreated via catalysis:treated via catalysis:Catalytic convertersCatalytic converters, typically , typically composed of composed of platinumplatinum andand rhodiumrhodium, break down some of , break down some of the more harmful byproducts of automobile exhaust.the more harmful byproducts of automobile exhaust.


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2 CO + 2 NO 2 CO2 CO + 2 NO 2 CO 22 + N+ N 22

With regards to synthetic fuels, an old but still With regards to synthetic fuels, an old but stillimportant process is theimportant process is the FischerFischer-- Tropsch synthesis Tropsch synthesisof hydrocarbons fromof hydrocarbons from synthesis gassynthesis gas, which itself is, which itself is

processed via , catalysed by iron.processed via , catalysed by iron.

BiodieselBiodiesel and related biofuels require processing and related biofuels require processing via both inorganic and biocatalysts. via both inorganic and biocatalysts.

Fuel cellsFuel cells rely on catalysts for both the anodic andrely on catalysts for both the anodic andcathodic reactions.cathodic reactions.


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2 . Bu lk c hemi c als 2 . Bu lk c hemi c als

Some of the largestSome of the largest--scale chemicals are produced viascale chemicals are produced viacatalytic oxidation, often using catalytic oxidation, often using oxygenoxygen. Examples include. Examples includenitric acidnitric acid (from ammonia),(from ammonia), sulfuric acidsulfuric acid (from(from sulfursulfur

dioxidedioxide toto sulfur trioxidesulfur trioxide by theby the chamber processchamber process ), ),terephthalic acidterephthalic acid from pfrom p--xylene, andxylene, and acrylonitrileacrylonitrilefromfrompropane and ammonia.propane and ammonia.

Many other chemical products are generated by largeMany other chemical products are generated by large--scalescalereduction, often viareduction, often via hydrogenationhydrogenation. The largest. The largest--scalescaleexample isexample is ammoniaammonia, which is prepared via the, which is prepared via the HaberHaberprocessprocess fromfrom nitrogennitrogen.. MethanolMethanol is prepared fromis prepared from carboncarbonmonoxidemonoxide..


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Bulk polymers derived fromBulk polymers derived from ethyleneethylene andandpropylenepropylene are often prepared viaare often prepared via ZieglerZiegler--NattaNattacatalysiscatalysis. P olyesters, polyamides, and. P olyesters, polyamides, and isocyanatesisocyanatesare derived viaare derived via acidacid--base catalysisbase catalysis..

MostMost carbonylationcarbonylation processes require metalprocesses require metalcatalysts, examples include thecatalysts, examples include the Monsanto aceticMonsanto acetic

acid processacid process andand hydroformylationhydroformylation..


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3 . F i n e c hemi c als 3 . F i n e c hemi c als

Many fine chemicals are prepared via catalysis; Many fine chemicals are prepared via catalysis; methods include those of heavy industry as well asmethods include those of heavy industry as well asmore specialized processes that would bemore specialized processes that would be

prohibitively expensive on a large scale. Examplesprohibitively expensive on a large scale. Examplesincludeinclude olefin metathesisolefin metathesis using using Grubbs' catalystGrubbs' catalyst ,,thethe Heck reactionHeck reaction , and, and FriedelFriedel--Crafts reactionsCrafts reactions..

Because most bioactive compounds areBecause most bioactive compounds are chiralchiral,,many pharmaceuticals are produced by many pharmaceuticals are produced by enantioselective catalysis.enantioselective catalysis.


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Chapter 1 Intro to Catalysis