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Catalysis
1
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
4
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. - - - -
5
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
6
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)
10
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
11
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
12
Effect of Catalyst on Reaction Profile and Activation Energy
13
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.
17
Induced-fit Model of Enzyme Action
Lock and key Model by Emil Fischer in 1894
18
Effect of Substrate Concentrationon Rate: [Enzyme] = Constant
19
Effect of Enzyme Concentrationon Rate: [Substrate] = Constant
20
Enzyme Activity as a Functionof Temperature
21
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.
22
A Surface-Catalyzed Reaction
23
Catalytic Reaction Steps
Adsorption
CO
O2
Surfacediffusion
Precursor
Surfacereaction
Desorption
2CO
24
25
26
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
12
H < 0exothermic
H2+C4H6C4H8
Ferrite spinelse.g. MnFe2O4, Zn(Cr2-xFex)O4
dehydrogenation endothermic metal catalyst, high temp. rxn., easily cokingH > 0
27
Transition Metal oxide catalysts (continue)
Rxn Catalyst
Naphthalene or o-xylene + air phthalic anhydride
28
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
29
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
31
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
33
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
36
F.C.C.
520-5400C
~ 7000C
C + H2O CO + H2
37
38
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
41
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
42
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
46
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%)
48
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
49
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.
50
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
51
back-extrapolating
52
53
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
54
Co-precipitation
Mixing of the solutions of metal and support presursors
55
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
56
Calcination
Reduction
Drying the solid mixture
Impregnation
Suspending the solid support material in the solution of metal presursors
57
Calcination
Evaporating the solvent
Drying the solid mixture
Reduction
Metalsunpaired d-eletrons, the activity of the metal surface
58
Volcano curve
59
60
M- H
Mn, 3d5Cu, 3d10
61
62
63
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
64
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
65
Fats & Oils
66
12 C
14 C
16 C
18 C
67
68
69
Hydrogenation of unsaturated lipids
70
Edible-oil reduction
71
72
Stearic acid
73
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-
74
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
76
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
77
The Catalytic ConverterThe catalytic converter consists of Rh, Pt and Pdparticles on an Al2O3/CeO2 wash-coat deposited on amonolith of cordierite
78
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
79
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
80
Fuel cells
Liquid electrolyte : AFC, PAFC, MCFCsolid electrolyte: PEMFC, SOFC
Low temperature: AFC, PAFC, PEMFChigh temperature: MCFC, SOFC
81
Fuel cells Concept of solid oxide fuel cell (SOFC)
82
Fuel cells Concept of proton-exchange membrane fuel cell PEMFC
83
The catalysts for fuel cells
84
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
85
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
87
88
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
89
Consideration in supported metal catalyst
(1) metal particle size effect
(2) support effect
(3) metal-support interaction
90
(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
91
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
92
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:
93
facile
demanding
94
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
95
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
96
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
97
98
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
99
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
101
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.
102
Poisoning an impurity in the feed stream alters the surface composition of the metals.
1. stronger chemisorbed than reactants2. alloy formation
by
Electronegative Species:
103
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
104
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.
105
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
106
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