Catalysis

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Catalysis ApplicationsCatalysis Applications

World catalystsWorld catalysts 9 G$ business in 1999 24% for Refining, 24% for Chemicals,

23% for Polymers, 29% for Environment

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3

oxidation

According to Dept. Energy, USA, in 2003

Catalysis & Catalytic processes are responsible for about 20% of the U.S. gross domestic product (all goods and services) the keys to future gains in energy efficiency, environmental stewardship and attendant economic prosperity for the country

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The twelve principles of Green Chemistry1. It is better to prevent waste than to treat or clean up

waste after it is formed.2. Synthesis methods must be designed to maximize the

incorporation of all materials used in the process into the final product.

3. Whenever practicable, synthetic methodologies should be designed to use and generate substances that possess little or no toxicity to human health and the environment.

4. - - - -9. Catalytic reagents (as selective as possible) are

superior to stoichiometric reagents.10. - - - -

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Early History of Catalysis

Neolithic age ( ~5000B.C.)

Biocatalytic fermentation in wine manufacture

500B.C.

Soap manufacture (hydrolysis of animal fats with potash lye)

1500A.C.

Alchemists formed sulfuric acid by a mysterious catalytic process

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1831

Pelegrine Phillips (a Bristol vinegar manufacturer) obtained the 1st known patent in catalysis for the reaction

SO2 + air SO3 (Pt sponge as catalyst)

The catalyst used now-a-day is V2O5/ SiO2

1835

J.J. Berzelius coined the word catalysisGreek words cata means down

lysis means split or break7

This new force, which is unknown until now, is common to both organic and inorganic nature. I do not believe that it is a force completely independent of electrochemical affinities; It is more convenient to give this force a separate name. I would therefore call this the catalytic force. I would furthermore, call the decomposition of substances resulting from this force catalysis, just as the decomposition of substances resulting from chemical affinity is calledanalysis.

1880 Carl Groebeaccidentally broke a thermometer while stirring a mixture of hot naphthalene and H2SO4 phthalic anhydride & phthalic acid dye chemistry

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1899 Arrhenius equation k = A exp(-Ea/RT)

1903 Ostward process

2NH3 + 7/2 O2 2NO2 + 3 H2O (Pt sponge as

catalyst) HNO3 industry

1909 Ostward (German) received Nobel Prize

for studies of reaction rate over catalysts

1912 Paul Sabatier (French) received Nobel Prizefor studies of catalytic hydrogenation of organic

compounds9

1915 Haber Process

N2 + 3 H2 2 NH3 (Fe catalyst)

1919 Fritz Haber (German) received Nobel Prize

1920 Sabatier published the 1st book on catalysis

1923 Methanol synthesis

CO + 2 H2 CH3OH (Cr2O3-ZnO catalyst)

1930 Fischer-Tropsch Process

CO + H2 (CH)n (Fe catalyst)

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1932 Langmuir (USA) received Nobel PrizeFor surface chemistry and Langmuir isotherm

1936 Modern era in catalysis

Catalytic cracking of petroleum (acid treated clays as catalyst)

BET surface area

Deuterium discovery isotope research

1963 Ziegler (German) & Natt (Italian)received Nobel Prize for stereoregulatedpolymerization catalyst

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Three Classes of Catalysts

Heterogeneous- The catalyst and the reactants are in different phases

Homogeneous- The catalyst and the reactants are in the same phase

Biological - Enzymes

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Effect of Catalyst on Reaction Profile and Activation Energy

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Reaction profiles for theuncatalyzed and catalyzed decomposition of ozone

Homogeneous Catalysis

Homogeneous CatalysisProduction of acetic acid

1916 acetyleneacetaldehydeacetic acid1950-1960 oxidation of n-butane or naphtha1955 homogeneous methanol carbonylation use

Ni catalyst by BASF1960 iodide-promoted CO catalyst under 2300C

600atm yield 90%1970 Monsanto synthesis use Rh complex

(180-2200C 30-40atm) yield 99%1980 Celanese and Daicel improve Monsanto

process adding LiI or NaI1996 use Ir-based process improved Celanese process1997 direct oxidation of ethylene by Denko

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Production of acetic acid

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Methanol carbonylation- Rh catalyzed methanol carbonylation

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CH3OH + CORh complex

CH3COOH180-2200C30-40atm

r.d.s Rate [cat.][CH3I]

14-15wt.% of H2O is required

Enzyme Catalysis Enzymes are high-molecular-mass proteins that

usually catalyze one specific reaction or a set of quite similar reactions but no others.

Extremely high selectivity The reactant substance (S), called the substrate,

attaches itself to an area on the enzyme (E) called the active site, to form an enzyme-substrate complex (ES).

The rates of enzyme-catalyzed reactions are influenced by factors such as concentration of the substrate, concentration of the enzyme, acidity of the medium, and the temperature.

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Induced-fit Model of Enzyme Action

Lock and key Model by Emil Fischer in 1894

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Effect of Substrate Concentrationon Rate: [Enzyme] = Constant

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Effect of Enzyme Concentrationon Rate: [Substrate] = Constant

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Enzyme Activity as a Functionof Temperature

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Heterogeneous Catalysis Many reactions are catalyzed by the surfaces of

appropriate solids.

Steps in heterogeneous catalytic reactions1. Diffusion to the surface2. Adsorption of reactants3. Surface diffusion of reactants4. Surface reaction5. Surface diffusion of products6. Desorption of products7. Diffusion away from the surface

Heterogeneous catalysis requires balance of adsorption, reaction, and desorption

Catalyst strongly adsorbing > no rxn.Catalyst weakly adsorbing > no rxn.

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A Surface-Catalyzed Reaction

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Catalytic Reaction Steps

Adsorption

CO

O2

Surfacediffusion

Precursor

Surfacereaction

Desorption

2CO

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25

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Rxns catalyzed by Metals Catalyst High activityH-D exchange most trans. metals W, Pthydrogenation Group

skeletal isomerization of (HC)n Pt, Ir, Pd, Au Pt

dehydrogenation Group Ptoxidation Ag

Ag

AuAu, Pt metals Pt

Pt metals Pt

Pt metals Rh

Ni, Co, Pt metals Ni,Pt

hydrogenolysis Group

double bond shift Pt metals PdRu, Rh, PdOs, Ir, Pt

CH2=CH2 CH2 CH2

O+O2

CH3OH HCHOO2+

CO CO2O2+

Ostwald process

NO CO+2 2 CO2+2N2

CH4 + H2O CO + H2

+ 6454 + O2 H2ONONH3850oC

Transition Metal oxide catalysts

Rxn CatalystCu2O or multimetallic oxidee.g. Bi2O3-MoO3

Propylene acrolein + acrylic acid

Complex metal molybdatesor multimetallic oxidee.g. CdMoO4,

M8FeBi(MoO4)12O12

Co2+, Ni2+

C3H6 CH2 CH CN +O2, NH3

H2OOne-step ammoxidationto acrylonitrile

butane butadiene

OxidativedehydrogenationC4H8 + O2 C4H6 + H2O

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H < 0exothermic

H2+C4H6C4H8

Ferrite spinelse.g. MnFe2O4, Zn(Cr2-xFex)O4

dehydrogenation endothermic metal catalyst, high temp. rxn., easily cokingH > 0

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Transition Metal oxide catalysts (continue)

Rxn Catalyst

Naphthalene or o-xylene + air phthalic anhydride

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Supported V2O5

n-butane maleic anhydride (VO)2P2O7

Butene (or benzene) + air maleic anhydride

(VO)2P2O7, (V2O4/MoO3)

SO2 O2 SO3 H2SO412

+ V2O5 + K2SO4 /SiO2

CH3OH lean Fe2O3-MoO3CH3OH rich Ag

Solid acid catalysts

(i) alumina & acid-treated clays(ii) aluminosilicate (incorporation of alumina in silica)

silica-alumina(iii) protonated zeolites behave as highly acidic solutions

(amorphous)

(crystalline)

shape selectivity acid amount no. of Al acid strength 1 / no. of Al

(iv) super acidsH0

-14.5-16.0-12.9

TiO2ZrO2Fe2O3

H2SSO4-2SO2

+ calcination

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Liquid super acids H0-11.9-13.0-13.8-15.1-14.1

< -13.2< -14.5

100% H2SO4HClO4ClSO3HFSO3HCF3SO3HSbF5AsF5

Bronstedsuper acid George Olah

1994Nobel Prize winner

Lewissuper acid

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AcidStrength

Acid-Catalyzed Rxns

Isomerization (alkene double-bond isomerization;trans, cis-isomerization)

Alcohol dehydrationPolymerizationCrackingSkeletal isomerizationAlkylation

Acylationincreases

e.g.

Disproportation

CH3

+ CH3OH + +

CH3

CH3

CH3

CH3

CH3CH3

+CH3 C

O

O CH3

CH3 C

O

Cl

C CH3

O

CH3 CH3CH3

CH3

CH3

CH3

CH3

+ ++2

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Solid basic catalysts less used, and less developed

MgO (/Li2O), CaOK/Al2O3KNH2/Al2O3M-zeolites (M: Li < Na

Base-Catalyzed Rxns

dehydrogenation

aldol condersation

Side-chain alkylation with methanol

CH3CH2CH3

OHCH3CH2CH3

O

CH3CH CH2

+

+ H2O

H2

CH3CH2CH3

OCH3CCH2C

O OH

CH3CH3

CH3CCH

O

C

CH3

CH3

H2O-

acid-catalyzed

base-catalyzed

+ H2OCH3OH+

CH3 CH2CH3

CH2CN CH3OH+ CHCN

CH3

H2O+623K

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Cracking rupture of C-C bondsendothermic rxn. favored by high Temp.

Thermal cracking production of ethyleneCatalytic cracking production of gasoline

gas-oil (C13 ~ C25) gasoline + gases(C5 ~ C12) (< C4)

Octane number ratingn-heptane 0iso-octane 100(2,2,4-trimethylpentane)

Catalyst activity falls down very quickly ~ 15 min F.C.C.

Fluid catalytic cracker 34

Thermal cracking large amount of ethyleneCH4

small amount of olefinsat ~900oC

free-radical mechanisms

CR1

H

HCH

HR2 R1 C

H

HCH

HR2+

empirical rule: C-C bond scission at C-C bond to C atom having unpaired e-

RCH2-CH2-CH2 RCH2 + H2C=CH2-scission

'

CH3 RCH2CH2CH2CH2CH2R+ CH4 RCH2CH2CH2CHCH2R+

Random position

-scission

RCH2CH2 H2C CHCH2R+35

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F.C.C.

520-5400C

~ 7000C

C + H2O CO + H2

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39Octane boosters

Catalytic cracking 400 ~ 600 oC

Carbocations as intermediate initiation

Olefins + Brnsted acid

Paraffins + Lewis acid abstraction of H- ion

H2C CHCH3 H+ H3C C

HCH3+

RH L R LH-+ +

R2H R1HR1 R2+ +saturated

Easily from olefinsTherefore, adding small amount of C=C-R, usually enhancethe cracking rate of paraffins

Stability of carbocations

3o >2o >1o40

Rxn. of carbo-cation ions1 isomerization

H2C CH CH2CH2CH3 H3C CH CH CH2CH3

CH2CH2CH3H2C CH

-H+

H+

2 -scission

paraffin

-scission

H- migration

-scission

H--transfer

Propagation

2 H--transfer

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3 Alkyl migration

4 Termination

alkyl migrationH- migration

H--transfer

termination

CH3 C

CH3

CH2CH2R CH3 C CHCH2R

CH3

-H+

CH3CH3CHCH2CH2R CH2CHCH2CH2R

CH3

CH3 C

CH3

CH2CH2R

CH3 C CHCH2R

CH3

R' CH3CHCH2CH2R

CH3

+

- H+

R'H

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Zeolite catalysts

Zeolites become important in catalytic industry, when it was discovered that rare earth and hydrogen-form zeolites possessed cracking activity several order of magnitude greater than that of conventional silica-alumina catalyst.

To obtain the same conversion

Temp. (0C) 540

Zeolites increase activity for hydrogen-transfer rxn. among product molecules.

olefins, naphthene paraffin, aromatics more C5~C10 products, less C3, C4 products lower rate of coke formation

polyaromatic structure

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Table 5 Thermodynamic Distribution of Isomers at Different Temp.

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HCs -6 38 66 93Butanes

n- 15 25 35 43

2-methylpentane (MP) 20 28 34 36

n-hexane 4 11 14 17

Pentanes

n- 5 15 22 29neo- 0 0 0 0

Hexanes

2,3-dimethyl butane 11 10 9 9

3-methylpentane 8 13 15 17

iso- 85 75 65 57

iso- 95 85 78 71

2,2-dimethyl butane (DMB) 57 38 28 21

(C)

Mechanism of n-hexane isomerization over superacidStep 1. formation of carbocation

+ H2

H H

Step 2. hydride or alkide shift

isomers

Step 3. hydride transfer from alkane to incipient carbenium ion

iso-R + iso-RH +

n-hexane

2MP 3MP

2,3 DMB2,2 DMB

alkidemigration

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Nanotechnology of Catalysis

Catalysts are perhaps the first industrial nanotechnology

2-10 nm particles (sometimes larger) on high surface area support (Al2O3, SiO2)

Automotive catalyst:nm Pt on -Al2O3 47

Catalyst Particles

Catalytic reactions occur on catalyst surfaces

Small particles maximize surface area- optimize use of catalysts

(more metal atoms at surface)

Catalyst dispersionfraction of catalyst atomsat surface (10-40%)

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O2

O OOOOC

OC

2 CO

2 CO 2

Turn-over

Reactive site

Catalyst TurnoverTurnover rate [=] s1: number of reaction cycles completed at a catalyst site per second

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Supported metal catalysts

objective: to increase the effective surface area of metals

e.g. (i) Pt of finely divided particles in 1m-diameter

dispersion ~ 0.001

T

S

NN

==atoms totalof no.

atoms surface of no.dispersion

(ii) Commercial Pt reforming catalyst dispersion 0.5

dispersion , effective S.A.

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usually measured by chemisorption1S.A. effective = smm nXn

Where Xm=no. of metal atoms/adsorbate molecule

nm=monolayer adsorbate uptake

ns=no. of metal atoms/unit area

obtained from low index crystal plane

MCuAuFeNiPdPt

ns (atoms/1019m-2)1.471.151.631.541.271.25

=102

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back-extrapolating

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Preparation of supported catalysts

1. Determination of the catalyst used

type of reaction

literature

modification based on knowledge of catalysis

2. Choice of metal presursors

loading, usually 1~10%

solubility and availability

if possible, avoid chloride, bromide, sulfate

General Procedures of Preparing Supported Catalysts

Impregnation or Co-precipitation

Calcination

Reduction

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Co-precipitation

Mixing of the solutions of metal and support presursors

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Calcination

Co-precipitation by adding base

Filtering the precipitate, washing & drying

Reduction

Incipient wetness impregnation

Dissolving the metal precursor in the solvent of the volume close to the pore

volume of the support

Adding the metal precursor solution onto the solid support material drop by drop

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Calcination

Reduction

Drying the solid mixture

Impregnation

Suspending the solid support material in the solution of metal presursors

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Calcination

Evaporating the solvent

Drying the solid mixture

Reduction

Metalsunpaired d-eletrons, the activity of the metal surface

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Volcano curve

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M- H

Mn, 3d5Cu, 3d10

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Percentage distribution of products from the reaction of

ethene with deuterium over some group VIII metals

Ethenes EthanesMetal T(K) C2H4-mDm C2H6-nDn C2H6

Pd 310 52.1 23.4 24.5Pt 327 10.6 70.1 19.3

Ir 360 11.8 83.6 4.6

Rh 350 72.6 23.9 3.5

Pd, Rh: Rate of alkene desorption > Rate of alkene reductionPt, Ir: Rate of alkene desorption < Rate of alkene reduction

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Selective hydrogenationCH2=CH-CH=CH2 + H2 CH2=CH-CH2CH3

To achieve high selectivity of butene:

Rate of desorption of alkene > Rate of alkene reduction

Pt, Ir: Poor for alkene isomerization; going to complete reduction

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Fats & Oils

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12 C

14 C

16 C

18 C

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Hydrogenation of unsaturated lipids

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Edible-oil reduction

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Stearic acid

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Ag catalyst for ethylene oxidation

CH2 CH2 O2Ag

CH2 CH2

O

CO2

+230oC

Adsorption

O2 O2

O2-2

2O2-

(ads. on 4 adjacent Ag+) Ea ~ 3 kcal/mol

(ads.) Ea ~ 8 kcal/mol

(ads.) Ea ~ 20 kcal/mol

Can be blocked by Cl-, selectivity

fastprocess

Mechanism

CH2 CH2(g) +

Ag

O

O CH2CH2O

O

Ag

CH2O

CH2

Ag

O-

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Effect of pore volume

Partial oxidation or reduction products will be completely oxidized or reduced if trapped in pores.

High surface area catalysts are usually avoided.

(i)

CH2 CH2

OCH2 CH2 O2

Ag+

230oCepoxide

+ CO2 by-product(ii)

C CH

H

H

H+

Pt,Pd, NiH2 C C

H

H

H

H

H

H

important in food industry; C=C not completely remove to avoid hardening 75

Automotive Emission Control

carbon monoxide (CO, 0.5 vol.%)unburned hydrocarbons (HC, 350 vppm)nitrogen oxides (NOx, 900 vppm)hydrogen (H2, 0.17 vol.%)water (H2O, 10 vol.%)carbon dioxide (CO2, 10 vol.%)oxygen (O2, 0.5 vol.%)CONOxHC

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Automotive Emission Control

Largest use of Pt, Pd and Rh industrially

Example of typical heterogeneous catalytic reaction

Three-way catalyst: Pt/Pd/Rh on CeO2

Pt/Pd: CO + 1/2 O2 > CO2Pt/Pd: HC + O2 > CO2 + H2O

Rh: NOx + HC(CO) > N2 + CO2 + H2O

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The Catalytic ConverterThe catalytic converter consists of Rh, Pt and Pdparticles on an Al2O3/CeO2 wash-coat deposited on amonolith of cordierite

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Three Way Converter

OxygensensorEngine

Catalyst

AcceleratorAir

Fuel

Exhaust

Computer

Pt/Pd/RhCeria washcoat

A/F ratio

14.914.614.30

100

Conv. %CO

NOx

HC

stoic

Poisoning of the catalyst: Pb, S

desulfurizationunleaded gasoline is neccessary

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Catalyst Support Effects

Note cyclic operation of catalytic converterFuel lean: CO, HC oxidationFuel rich: NOx reduction

Yet oxidation and reduction continue even when the A/F mixture favors the opposite reaction!

How does this occur?

CeO2 acts as an oxygen storage medium

Fuel rich: Oc + Ce3+ > Ce4+ (i.e. CeO2)

Fuel lean: CeO2 > Ce3+ + O

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Fuel cells

Liquid electrolyte : AFC, PAFC, MCFCsolid electrolyte: PEMFC, SOFC

Low temperature: AFC, PAFC, PEMFChigh temperature: MCFC, SOFC

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Fuel cells Concept of solid oxide fuel cell (SOFC)

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Fuel cells Concept of proton-exchange membrane fuel cell PEMFC

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The catalysts for fuel cells

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Nanoscale Effects in Catalysis

Are catalyst particles simply small versions of the catalyst material?

Does the nanoscale influence catalytic properties beyond simply presenting more surface atoms?

What possibilities exist for nanoscale modification of catalyst behavior?

1. Modification of electronic structure2. Interaction of different structure surfaces3. Spill-over effects/other support interactions4. Variation in fluid phase transport properties

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Catalyst Size Effect- I

Figure 2. (a) Cyclic voltammograms of carbon-supported Pt catalyst samples recorded in 0.1 M HClO4 solution; T= 20 C, scan rate 50 mV/s; currents are normalized to the measured Pt surface area (Hupd charge after double layer correction); HRTEM images of a carbon-supported Pt nanoparticle (b), and the nanostructured Pt film supported on organic whiskers (c).

J. AM. CHEM. SOC. 127, (2005) 682186

EXAFS of Pt/C and Pt-alloy/C catalysts[S. Mukerjee, J. McBreen, J. Electrochem. Soc. 146 (1999) 600.]

Change in d-band density

particle size / nm

2 4 10

Effect of change in potential of 0-0.54 V

0

0.22

Pt/C

Pt d-band density

Pt-Pt bond distance / nm

2.66 2.78

Pt-alloy effects

Pt/Ni/C

Pt/Co/CPt/Fe/C

Pt/Cr/C

Pt/Cr/C optimal for O2 reduction due to optimal d-band vacancy

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Active sites on edge

Active sites on terrace

TOF = (AR)/(FE)Atomic rate

Fraction expose

demanding

facile

Catalyst Size Effect- II

structure-insensitive

structure-sensitive

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Consideration in supported metal catalyst

(1) metal particle size effect

(2) support effect

(3) metal-support interaction

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(1) Metal particle size effect Adv. Catal. 36, 55 (1989)

atom clusters bulk metallic particle

geometry coordination number chemical properties

change a lot for particles 55 atoms

~ 1 nm diameter

Particle size effect, usually investigated in the range of 10 ~ 50 in diameter. When > 40-50 , the crystals exhibit bulkbehavior

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1969, Boudant divided catalytic rxns over metals into 2 systems

Adv. Catal. 20, 155 (1969)

demanding rxn. structure-sensitiveTON changes with percentage dispersion, alloying, or poisoning

facile rxn. structure-insensitive

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facile rxn. the active site may be a single surfaceatom

e.g. simple hydrogenation rxn. of 1-hexene, cyclohexene, benzene, allyl alcohols.

demanding rxn. the active site may be several surface atoms whose arrangementrelative to each other is critical

e.g. rxns involving C-C breaking, hydrogenolysis, skeletal isomerization.

electronic effectgeometric effect

possible explanation:

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facile

demanding

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Reaction on NanocatalystsH2/O2 reaction at 1000 K

(nonflammable mixture in Ar)

H2 + 1/2 O2 > H2O

[S. Johansson, K. Wong, V.P. Zhdanov, B. Kasemo, J. Vac. Sci. Tech. A 17 (1999) 297.]

130 nm Pt/CeO2 fresh and after 10 min of reaction

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Equilibrium Particle Shape

Reaction alters particle shape!

Polycrystalline particles become crystalline

Large particles disintegrate to faceted crystals

500 nm Pt/CeO2 (a) fresh and (b) after 10 min of reaction

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Influence of Surface Reaction

Role of oxygen as reactant- Oxygen adsorption weakens Pt-Pt bonds- Pt (in oxide form) becomes more mobile- Effects not seen for H2, H2O

Energy transfer from reaction- Adsorption highly exothermic (2.5 eV/t.o.)- High reaction rates (t.o. 103!)

Local temperature increase

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3. interparticle transport

2. particle migration

transfer is strongly dependent on the gas environment

Sintering and Mobility

1. atom migration

rapid up to particle radius of ~50

Sintering and Mobility

3. interparticle transport

RuO4 mp. 25 C, bp. 40 COsO4 mp. 40 C, bp. 130 C

e.g. in O2, metals form volatile metal oxidesin CO, metals form carbonyl species

transfer is strongly dependent on the gas environment

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In an inert or reducing atmosphere

force cohesive1growth particle Tammann Temp. 0.5 Tm.p.(K)

Htting Temp. 0.3 Tm.p.(K)

Lattice becomes appreciably mobile

Surface becomes approciably mobile

stability of metal particles cohesive force mp..

Ag(916)

In Oxygen

At high temperatures (>600)Sintering follows the normal pattern, increases as Temp , or Time

Stability of metal particles Hf of metal oxides

Os < Ru < Ir < Pt < Pd =Rh

experimental result: Ru < Ir < Pt < Rh

At moderate temperature range redispersion

e.g. Pt/Al2O3 increasing in dispersion by treating in O2at 400~600 , (optimum temp. 550 ), for short period of time

Ir/Al2O3 at 400

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Mechanism of redispersion:Metal oxide molecules detached from the crystallites migrate to a surface site and become fixed by forming a surface complex with the support.

Upon subsequent reduction, some re-agglomeration occurs

In the presence of a liquid phase, crystallite growth of a supported metal may occurs much more readily than in a hydrogen environment.

Many metals dissolve to a very slight extent in a variety of nonaqueous liquids.

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Poisoning an impurity in the feed stream alters the surface composition of the metals.

1. stronger chemisorbed than reactants2. alloy formation

by

Electronegative Species:

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S2-,CO,PH3,O2 & H2O

Cl-,P compounds,Other metals

for metals used as catalysts under reduction conditions, e.g. Fe for NH3synthesis is poisoned by forming metal oxide.

from salt contamination, or from Cl2 in waterfrom lubricating oil

Electronic effect from S

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Promoter a small amount of species on the catalyst or in the feed stream to improve the catalytic activity or selectivity.

Electropositive Species: e.g. alkaline metals

In CO hydrogenation, adsorbed K increases the rate of CO dissociation on Ni(100), increase carbon level, and increase therate of formation of higher hydrocarbons.

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Summary

Catalysts are an existing nanotechnology

Nanotechnological aspects of catalysis only just beginning to be understood

More effects to explore- Modification of electronic structure- Interaction of facets- Interaction with support (spillover effects)- Mass transport resistances- Confined space reactions and catalysis

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CatalysisCatalysis ApplicationsEffect of Catalyst on Reaction Profile and Activation EnergyHomogeneous CatalysisEnzyme CatalysisInduced-fit Model of Enzyme ActionEffect of Substrate Concentrationon Rate: [Enzyme] = ConstantEffect of Enzyme Concentrationon Rate: [Substrate] = ConstantEnzyme Activity as a Functionof TemperatureHeterogeneous CatalysisA Surface-Catalyzed ReactionPercentage distribution of products from the reaction ofethene with deuterium over some group VIII metalsThe Catalytic ConverterFuel cellsFuel cellsFuel cellsThe catalysts for fuel cells