Modern Methods in Heterogeneous Catalysis Research
Acid-Base Catalysis Application of Solid Acid-Base Catalysts Annette Trunschke 18 February 2005
Outline 1. Introduction - basic principles 2. Substrates and products 3. Kinds of acid / base catalysts - examples 4. Characterization of surface acidity / basicity - examples 5. Acid catalyzed reactions 6. Base catalyzed reactions 7. Acid-base bifunctional catalysis 8. Summary and outlook
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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1. Introduction - Basic definitions concept
acid
base
Brønsted
H2O
OH-
Lewis
FeCl3 +
Cl-
+
H+ [FeCl4]-
Hydrogen transfer reactions intermediates acid-catalyzed
carbenium ions
+ H+
base-catalyzed
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
+ H+
carbanions
3
1. Introduction - Basic definitions
active species
specific acid / base catalysis
general acid / base catalysis
H3O+ or OH-
undissociated acid or base groups; a variety of species may be simultaneously active
reaction •in solution medium / •on the surface of conditions a hydrated solid
•gas phase reactions •high reaction temperatures
Advantages of solid acid-base catalysts: • • • •
Easier separation from the product Possible reuse and regeneration Fewer disposal problems Non-corrosive and environmentally friendly (but not always!)
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2. Substrates and products solid acid catalysis
solid base catalysis
substrates •Alkanes, aromatics (components of crude petrolium) •Alkenes (products of petrolium cracking (FCC, steam cracking))
•Alkenes •Alkynes •Alkyl aromatics •Carbonyl compounds
products
•Chemical intermediates •Fine chemicals
•Gasoline components •Chemical intermediates •Fine chemicals
Industrial processes in 1999: 103 solid acids worldwide production by catalytic cracking: 500x106 tonnes/y 10 solid bases 14 solid acid-base bifunctional catalysts K.Tanabe, W.F.Hölderich, Applied Catalysis A 181 (1999) 399. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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3. Kinds of acid / base catalysts Solid acids
Solid bases
•Zeolites
•Oxides and modified oxides
ZSM-5, Mordenite, Y-zeolite, US-Y, Beta
Al2O3-NaOH-Na, Al2O3-KOH-K, ZrO2-KOH, ZrO2-K2O, MgO, MgO-Al2O3, hydrotalcites
•Oxides, phosphates
•Zeolites SiO2-Al2O3, Al2O3-BF3, SO42-(Mn,Fe)/ZrO2, SrHPO4, CsNaX, CsNaY, microporous FePO4, Li3PO4, phosphoric acid, titanosilicate ETS-10 SAPO-11, SAPO-34 •Mesoporous silicas modified 1.Ion-exchange resins Amberlyst, Nafion
•Clays
with amino groups •Cs/NPC •Oxynitrides
Kaolinite, Montmorillonite, pillared clays
AlPON, AlGaPON, ZrPON
K. Tanabe, W.F. Hölderich, Applied Catalysis A 181 (1999) 399. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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3. Kinds of acis / base catalysts - examples
Alumosilicates •Amorphous alumosilicates •Microporous zeolites (ZSM-5) •Mesoporous alumosilicates (MCM-41)
Brønsted acid site H O Al
H Si O Al O Si
O
Si
in H-exchanged zeolites
- H2O Al MFI viewed along [010]
Si O Al O Si
O
Si
MCM-41
d = 5.3x5.6 Å or extraframework Al3+
Lewis acid sites
www.iza-structure.org/databases/ Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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3. Kinds of acis / base catalysts - examples
Sulfated zirconia Structure of surface sulfates HSO4-/SO42-
S2O72-
A. Hofmann, J. Sauer, J. Phys. Chem B 108 (2004) 14652.
L.M. Kustov, V.B.Kazansky, F.Figueras, D. Tichit, J. Catal. 150 (1994) 143.
Brønsted sites
H
Surface acid sites O
O S
O
O Lewis sites O
Zr O Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
O
Zr
H O
S O
Zr
O O Zr 8
3. Kinds of acis / base catalysts - examples
Resins Styrene-based sulfonic acids (Amberlyst, Dowex, Lewatit) Prepared by copolymerization of styrene and divinylbenzene, sulfonation
Perfluorinated resinsulfonic acid (Nafion) Prepared by copolymerization of perfluorinated vinyl ether and tetrafluoroethylene, sulfonation
•Weak acid sites (Amberlyst-15: H0=2.2) •High number of acid sites, Amberlyst15: surface area 3.35 m2/g, pore volume 4.8 ml/g) •Thermally stable to about 120-140°C
•Strong acid sites (H0=11-13) •Small number of acid sites, surface area 0.02 m2/g, non-porous solid; asseccibility of acid sites improved in nanocomposites with silica •Thermally stable to about 280°C
B. Corain, M. Zecca, K. Jeřábek, J. Mol. Catal. A 177 (2001) 3.
K.A. Mauritz, R.B. Moore, Chem. Rev. 104 (2004) 4535.
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3. Kinds of acis / base catalysts - examples
Resins Morphology of styrene-based sulfonic acids
Hydrated protons in waterswollen ion exchanger catalyst
Undissociated acidic protons in a catalyst swollen in non-aqueous solvent B. Corain, M. Zecca, K. Jeřábek, J. Mol. Catal. A 177 (2001) 3. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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3. Kinds of acis / base catalysts - examples
Clays and pillared clays
Al2[Si2O5] (OH)4 Kaolinite
Al2[Si4O10] (OH)2 Montmorillonite
Acid sites: Brønsted (protons) and Lewis (metal ions) Z. Ding, J.T. Kloprogge, R.L. Frost, G.Q. Lu, H.Y. Zhu, Journal of Porous Materials 8 (2001). http://www.ill.fr/dif/3D-crystals/layers.html
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3. Kinds of acis / base catalysts - examples
MgO •Basic sites: •hydroxyl group •surface oxygen anions •Anionic charge of the oxygen is associated to the ionicity of the M-O bond and, therefore, always also to Lewis acidity
ions pairs Mg2+3cO2-3c Sites: •five coordinated sites on flat (001) faces (M2+5c and O2-5c) •four coordinated sites on steps and edges (M2+4c and O2-4c) •three coordinated sites on corners (M2+3c and O2-3c ) (c = coordinatively unsaturated).
progressive water attack on MgO
G. Spoto, E.N. Gribov, G. Ricchiardi, A. Damin, D. Scarano, S. Bordiga, C. Lamberti, A. Zecchina, Progress in Surface Science 76 (2004) 71. S. Coluccia, Stud. Surf. Sci. Catal. 21 (1985) 5. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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3. Kinds of acis / base catalysts - examples
Hydrotalcites and MgO-Al2O3 HT
D. Tichit and B. Coq, Cattech 7 (2003) 206.
CHT
[M2+1-xM3+x(OH)2]x+[Ax/n]n-1·mH2O; M2+= Mg2+; M3+=Al3+, A= CO32-, OHTheor. ratio Sample
Al/(Al + Mg)
Mg/Al molar ratio Theor.
Bulk
Surface
(ICP)
(XPS)
SBET 2
Vp
dpa
Cb
3
(m /g)
(cm /g)
(Å)
(wt%)
Weight lossc (wt%)
HT0.6 (MG30)
0.67
0.5
0.6
n.d.
163
0.32
76
1.42
n.a
HT1.4 (MG50)
0.44
1.25
1.4
n.d.
13
0.05
167
1.19
n.a
HT2.2 (MG61)
0.33
2.0
2.2
n.d.
15
0.05
128
2.42
n.a.
HT3.0 (MG70)
0.25
3.0
3.0
n.d.
20
0.10
205
2.27
n.a.
CHT0.6
0.67
0.5
0.6
0.8
257
0.52
81
-
31
CHT1.4
0.44
1.25
1.4
1.4
201
0.23
45
-
36
CHT2.2
0.33
2.0
2.2
2.0
114
0.13
46
-
42
CHT3.0
0.25
3.0
3.0
2.0
-
-
-
52 258
44
-
0.22 0.96
-
MgO
203 75
-
-
Al2O3
-
-
-
-
234
0.54
45
-
-
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3. Kinds of acis / base catalysts - examples
Basic zeolites •Basicity is related to framework oxygen
Na+ Na+ O O O O O Si Al Si Si Al Si
•Exchanging zeolites with a less electronegative charge balancing cation such as Cs+ creates a more basic zeolite (shift to lower O1s binding energies) •Occlusion of alkali metal oxide clusters or alkali metal clusters in zeolite cages •Anchoring organic bases at silanol groups of mesoporous alumosilicates ( e.g. 3-trimethyloxysilyl-propyl(trimethyl)ammonium chloride) – wide distribution of base sites
I. Rodriguez, S. Iborra, A. Corma, F. Rey, J.L. Jordá, Chem. Commun. (1999) 593. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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4. Characterization of acid / base properties Indicator methods The color change of an indicator B- is determined by the reaction B- + H+ -
B base indicator BH conjugated acid
BH [B-] H_ = pKBH+ log [BH]
Hammett acidity function
Louis P. Hammett, Alden J. Deyrup, J. Am. Chem. Soc. 54(7) (1932) 2721.
Tanabe et al., Stud. Surf. Sci. Catal. 51 (1989) 21: H_ is equal to the highest among the pKBH values of adsorbed indicators from which the basic site is able to abstract a proton (which can be protonated by the acid site). H_ < -12 „superacid“
H_ > 26 „superbase“
Disadvantages: •Approach is only applicable to Brønsted acid and bases of uniform strength. •Color change is not always related to the acid-base reaction, e.g., formation of charge-transfer complexes, colorless catalyst required Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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4. Characterization of acid / base properties
FTIR of adsorbed bases
G. Busca, PCCP 1 (1999) 723. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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4. Characterization of acid / base properties
Microcalorimetry Q [kJ/mol]
Q [kJ/mol]
Pyridine adsorption 250
S-SZ A-SZ Hβ
200
175
S-SZ A-SZ Hβ
150 125
150
100 100
75 50
50 0 0
200
400
600
800
1000
0
100
200
300
1200
V [µmol/g]
500 Vmid[µmol/g]
70°C in anisole
150°C, gas phase SZ=sulfated zirconia, preparation:
400
S-SZ precipitation of zirconia, sulfation A-SZ sol-gel procedure + S, supercritical drying
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4. Characterization of acid / base properties
Microcalorimetry CO2 adsorption, 40°C, gas phase 160
CHT0.6 CHT1.4 CHT2.2 CHT3.0
CO2, gas phase
140
Qdiff(kJ/mol)
120
Al2O3 MgO
100 80 60 40 20 0 0
40
80
120
160
200
240
CO2 uptake (µmol/g)
CHT = calcined hydrotalcites with Mg/Al ratios from 0.6 to 3 Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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4. Characterization of acid / base properties
CO2 as probe for basic sites Formation of bicarbonates by reaction of CO2 with basic OH groups H
O H
O C
O
O C
O
O
M
M
Free carbonate and surface carbonates formed by CO2 adsorption 2O
2O
O
O
C
C
O
O
O
M
M
D3h symmetrical
C2v
2O
2O
C
C O
O
M
2O
2O
C
C
O
O M
Cs unidentate
C2v
M
2-
O
O
C
O
O
O
O
M
M
M
M
C2v
Cs
bidentate
M
bridged
polydentate
Other probes: e.g., SO2, pyrrole, CHCl3, CH3CN, B(OCH3)3 J.C. Lavalley, Catal. Today 27 (1996) 377. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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4. Characterization of acid / base properties
CO2 TPD
1395
1653 1582 1435
250 200
1231
0.4
T / °C
150 100
2361
3619
ν(OH) in HOCO2-
Absorbance
monodentate or polydentate carbonate (?) δ(OH) in HOCO2
50 0
3500
3000
2500
2000
1500
Wavenumber / cm-1
Adsorption and temperature-programmed desorption of CO2 on MgO-Al2O3 (Mg/Al=0.6)
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4. Characterization of acid / base properties
UV-vis / Photoluminescence Direct measurement of the amount of surface O2-3c anions in defecive positions of MgO by photoluminescence: •To reveal the ion pair Mg2+3c-O2-3c, high pretreatment temperature is required. •At the same time, rearrangement of the surface is going on. •Such competition results in activity maxima as the pretreatment temperature is increased.
high surface low surface water attacked area MgO area MgO MgO
S. Coluccia, Stud. Surf. Sci. Catal. 21 (1985) 5.
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4. Characterization of acid / base properties
Iodine as a visible probe
The visible absorption band of iodine adsorbed on alkali metal-exchanged zeolite blue-shifts with increasing the electropositivity of the countercation and the aluminum content in the framework. S. Y. Choi, Y. S. Park, S. B. Hong, K. B. Yoon, JACS 118 (1996) 9377. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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4. Characterization of acid / base properties
Catalytic test reactions Double bond migration – 1-butene isomerization H2C=CH-CH2-CH3
+
H+
H3C-CH-CH2-CH3
H3C-CH=CH-CH3
+
H+
H3C-CH2-CH-CH3
HC H2C
CH2=CH-CH2-CH3 1-butene
CH CH3
+H+ +
-H
-H+ +H+
cis/trans ratio = 1
HC H3C
CH CH3
cis-2-butene
cis/trans ratio >> 1 +
-H+
H C
+H
CH3 CH
H2C
+H+ -H+
H C
CH3 CH
H3C trans-2-butene
H. Hattori, Chem. Rev. 95 (1995) 537. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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4. Characterization of acid / base properties
Catalytic test reactions Alcohol decomposition
+ H2O OH
acid
base
O + H2
OH
acid
+ H2O
base + H2O
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
H. Hattori, Chem. Rev. 95 (1995) 537. 24
5. Acid catalyzed reactions cis-transisomerization
secondary > primary
-12 -16
-19
-21
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
G.A. Olah, P.v.R. Schleyer, Carbonium Ions, Wiley, NY, 1968, p. 162.; A. Corma et al., J.Catal. 77 (1982) 159. 27
5. Acid catalyzed reactions
Formation of carbenium ion via carbonium ion intermediate
R
+
H C
R' R
H R
H C
R'
+
H2
H
H2 + C R' + H R CH2 R'
+ RCH3 + R'+
H
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5. Acid catalyzed reactions
Examples of alkylcarbonium ions CH5 +
H + H
CH3CH4
R C R R
Methoniumion
+
H-Ethoniumion
CH3 +
H3C
H3C
H
H
H
CH2CH3
+
H C-Cycloproponiumion
H H
H H
CH2
H-Cycloproponiumion
HH H
H H
C-Ethoniumion
H
+
H
+
H
2-C-Butoniumion H
H
H H
H H
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
H
+
H-Cyclobutoniumion
H
29
5. Acid catalyzed reactions
Intramolecular reactions of carbenium ions Hydride Shift
C
C
C
C
C
+
H~
C
C
H H3 C
O
C
C +
C
H
H H3 C O
Al HO
C
H
CH2 CH2 Si
C
Si OH
C
H3 C CH2
CH
O
O
O Si
CH3
Al HO
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
Si OH
Si
O Al
HO
Si OH
30
5. Acid catalyzed reactions
Intramolecular reactions of carbenium ions Alkyl Shift C
C
C
C
C
+
C
CH3~
C
C
C
C
C
C +
C
C
+
+
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
+
+
31
5. Acid catalyzed reactions
Intramolecular reactions of carbenium ions β-Elimination H +
H+
+
β-Scission +
+
+
H +
β-Scission & H-Shift
+
+
Cyclization H+
+
H +
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5. Acid catalyzed reactions
Intermolecular reactions of carbenium ions Hydride Transfer + +
+
H H C +
Disproportionation
+
+ +
+
Addition of alkenes / aromatics R' + CH-CH-CH3
R'+ + R-CH=CH-CH3 R
+ + +
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5. Acid catalyzed reactions
Carbocations on the catalyst surface
H
H C
H
C
H
H C
H
H
O
O Al
HO
CH3
C
H
Si
H
O Si
OH
π-bonding
Si
O Al
HO
CH2
H O Si OH
transition state
Si
O Al
HO
Si OH
σ-bonding
V.B. Kazanskii, I.W. Senchenya, J. Catal. 119 (1989) 108.
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5. Acid catalyzed reactions
Stabilization of carbenium ions on/in solid acids
Low energy adsorption sites for HMB in H-Beta ([100] direction) M. Bjørgen, F. Bonino, S. Kolboe, K.-P. Lillerud, A. Zecchina, S. Bordiga, J. Am. Chem. Soc. 125 (2003) 15863. See also: A.Corma, Topics in Catal. 6 (1998) 127.
FTIR-spectra of hexamethylbenene a) in KBr b) adsorbed on H-Beta c) adsorbed on dealuminated HBeta (free from protons)
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5. Acid catalyzed reactions
Skeletal isomerization of C5+-alkanes formation of a carbenium ion H2 C
H C H2
H2 C C H2
n
H C H2
H2 C
H C H2
m m
Cat: e.g. Pt/ chlorinated Al2O3 Shell Hysomer process: Pt/H-mordenite + H2
H2 C C H
H C C H2
CH
m
n m H
H
3>m≥1
hydride transfer
H
m≥3
n-C5H12 CH3
H2 C
CH C H2
C H2
H C H2
n
CH3 H
H C
H
C H2
H
m
H
CH C H2
isomerized products
C H
m
H
H
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
CH3
n +
Catalyst deactivation: Formation of unsaturated carbenium ions by hydride transfer between a carbenium ion and an alkene
CH C H2
n
n
+ C5H12
CH3 H2 C
H2 C
H3C C H2
H
m-2
cracked products
36
5. Acid catalyzed reactions
n-Butane isomerization Possible and forbidden rearrangements of the sec-butyl cation CH3
H2 C
H3C
1
C H2
3
b 4 CH3
H3C
a
H2 C
C H
CH2
H
H3C
a
b 4 H2
H3C
1
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
CH2
C
C2 H
3
CH3
37
5. Acid catalyzed reactions
n-Butane isomerization H3C-CH2-CH2-CH3
H2C=CH2-CH2-CH3
+ H2
CH3 + CH3
C CH3 CH3
CH3 H3C
UOP Butamer process: Pt/chlorinated Al2O3 + H2 Sun Refining: Fe/Mn/sulfated ZrO2
H3C
CH2-CH-CH2-CH3
C
CH3
CH3
http://www.uop.com/refining
H2 C
C
CH3
CH3
CH3 H3C
+
C
H2C
C
CH3
CH3
CH3 + H2
H3C
H C
CH3
CH3
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5. Acid catalyzed reactions
Isomerization of xylenes Mobil Oil: H-ZSM-5
A8 CH3
m
p
CH3
+H
CH3
H H
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
CH3
-H
CH3
CH3 H
o
H H
CH3
CH3
39
5. Acid catalyzed reactions
Cracking §Initiation:Mechanism depends on: §Reaction conditions §Feed composition §Brønsted- / Lewis site ratio §Propagation: §Ratio of hydride transfer to β-Scission (= product selectivity) can be controlled by catalyst composition §Termination: §β-Elimination (olefines) §Hydrid transfer to the carbenium ion (paraffines) Catalysts, e.g.: 5-40% HY or rare earth exchanged Y + silica/alumina binder + clay filler (UOP) Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
hydride transfer
H
β-scission hydride shift
Schematic catalytic cycle for the bimoleculare cracking of alkanes 40
5. Acid catalyzed reactions
Alkylation of isobutane with alkenes C4 cut from FCCU H2 Removal of Butadiene n-Butane i-Butane n-Butenes i-Butene
Recycle i-Butane
Methanol
Etherification
n-Butane i-Butane n-Butenes
Water Methyl-tert.Butyl Ether (MTBE)
Alkylation
n-Butane
Alkylate
Typical position of an alkylation unit in a modern refinery (FCCU: Fluid catalytic cracking unit) J. Weitkamp, Y. Traa in Handbook of Heterogeneous Catalysis, VCH, Weinheim, 1997, Vol. 4, p. 2049.
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5. Acid catalyzed reactions
Synthesis of MTBE/TAME macroporous sulfonic acid resin catalyst e.g. Amberlyst®-15, Dowex® M32
Chemical reactions to ethers CH3
CH2 + H3C
CH3OH
H3C
CH3
(MTBE)
CH3 CH3
CH2 + H3C
OCH3
C2H5OH
H3C
CH3
OC2H5
(ETBE)
CH3
CH3 H3C
C H
CH3 CH3 +
CH3 H2C
C H2
CH3OH
H3C
OCH3
(TAME)
C2H5 CH3
p=15-20 bar, T=60-80°C Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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5. Acid catalyzed reactions
Synthesis of MTBE/TAME Reaction steps in etherification Specific acid catalysis R-SO3H
+
CH3OH
CH3OH2
CH3
H3 C CH2 +
CH3OH2
H3C
+
C
H3 C
CH3OH
CH3 CH3H
CH3 H3C
C
+
CH3OH
H3 C
C
O
CH3
CH3
CH3H C
O
CH3
CH3
H3C
+
R-SO3
CH3 + R-SO3
CH3 Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
H3C
C
O
CH3 + R-SO3H
CH3 43
5. Acid catalyzed reactions
Alkylation of isobutane with n-alkenes Isobutane + C3-C5 alkenes = mixture of branched alkanes (alkylate) Conventional catalysts: HF: toxic H2SO4: consumption of 70-100 kg acid/ton alkylate New processes under development: •CF3SO3H/SiO2: Haldor Topsoe / Kellog FBA process •AlCl3/Al2O3 promoted by alkali metal ins + Ni, Pd, Pt (?) = HAL-100: UOP Alkylene process •Faujasite-derived catalyst: Lurgi Eurofuel Process
Zeol.
Isobutane
1-Butene
2,3-Dimethylhexane
Simplest mechanism for the formation of a dimethylhexane J. Weitkamp, Y. Traa in Handbook of Heterogeneous Catalysis, VCH, Weinheim, 1997, Vol. 4, p. 2049.
A. Feller, J. A. Lercher, Adv. Catal. 48 (2004) 229. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
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5. Acid catalyzed reactions
Friedel-Crafts acylation of aromatics
H3C
C
O + AlCl3
H3C
δ+ C O
δ− AlCl3
H3C
C
O + AlCl4
Cl
Cl
H
O + O C
C
C
CH3
CH3
AlCl3 CH3
O
+ AlCl4- HCl
O H2O
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
C
CH3
45
5. Acid catalyzed reactions
Solid acids in the acylation of aromatics Test reaction: Benzoylation of anisole O + O
C6H5
O
C6H5 - C6H5COOH
O
O
C6H5
4- and 2-methoxybenzophenone (96 / 4)
100 90 80
Ketone yield [%]
O
50°C, 3 h [solid acid]
71
70
59
60 48
50
Reaction mixture: 12 ml anisole 0.6 g benzoic anhydride 0.2 g solid acid
41
40 30 20
13
10
3
0
H-
mo
rde
Hnit
BE
e
A
K-
10
Am
be
rly
Su lfa ted n-H Batch sto 15 n S Zirco nia ilic a Na
fio
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
mode
46
5. Acid catalyzed reactions
Alkylation of aromatics R
+ C=C-C
base
acid
radical
R=CH3
R=H
R=CH3
C C
C
C
C
C
C
C
C C
C
cumene
isobutylbenzene
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
n-butylbenzene
47
5. Acid catalyzed reactions
Alkylation of benzene with ethylene Acid Catalyzed Synthesis of Alkylbenzenes + ArH
CH2=CH2 + HA
CH-CH3 A
[CH3-CH2-ArH] A
CH3-CH2-Ar + HA
Alkylation of benzene with ethylene Conventional catalysts:
New processes:
•
•H-ZSM-5 vapour phase (MobilBadger) •EBZ 500 zeolite liquid phase (UOP/Lummus)
•
Metal chlorides (liquid phase) Friedel-Crafts-catalysts BF3, AlCl3 (Monsanto-Lummus) Mineral acids HF, H2SO4 cumene + H2 C
C H
CH3
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
•High silica zeolite (Mobile-Badger/Raytheon •H-Beta (Enichem) 48
5. Acid catalyzed reactions
Alkylation of benzene with propylene
ZSM-5
H-Beta
www.accelrys.com/ cases/eniricerche.html
In ZSM-5, the bulkier cumene tends to isomerize to the less bulky n-propylbenzene.
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5. Acid catalyzed reactions
Alkylation of benzene with propylene Catalyst: H-Beta, EniChem
C. Perego, P. Ignallina, Catalysis Today, 73 (2002) 3. Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
50
6. Base catalyzed reactions RH + H2O → R- + H3O+ Acid
O
pKa
Acid
pKa
7
CH3OH
16
9
CH3CN
25
O H3 C
H
O
O
H
H
CH3COCH3
20
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
CH3
36
51
6. Base catalyzed reactions
Side-chain alkylation of aromatics Mechanisms of base catalyzed side-chain alkylation of toluene with propylene via a carbanion chain reaction
Initiation
CH3
-
R Na
CH2-Na+
+
+ RH
Addition
+ C=C-C=C
CH3
H2 C C H
CH2+
CH2=CHCH3
C-C-C=C-C
Na/K2CO3
CH2-
AMOCO Chemical, Teijin K.Tanabe, W.F.Hölderich, Applied Catalysis A 181 (1999) 399.
Addition CH3 H2 C C CH2H
CH3 +
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
CH3 H2 C C CH3 H +
CH2-
52
6. Base catalyzed reactions
C-C Bond Formation – Aldol Condensation H3C
C
CH3
+B
O Acetone H3C
C
C
C
CH2 + H+B
O H3C
CH2
C
+
H3C
O
H3C
O
H3C
H3C
CH3 H2 C C O + H+B
O
O B = e.g. La2O3, ZrO2 H3C
CH3
O
C
CH3 H2 C C O
C
CH3
CH3 H2 C C OH + B
O
CH3
Li/MgO Diacetone Alcohol alkali metal clusters in A-, X-, Y-, L-type zeolites -H O 2
H3C
C
CH3
O
Isophorone Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
(acid sites)
CH3 H3C
C
C H
O Mesityl Oxide
C CH3 53
6. Base catalyzed reactions
Formation of α-β unsaturated compounds Using methanol:
CH3OH
- H2
CH3COCH3 HCHO
CoxMg3-x(OH)4Si2O5
H3 C
-H2O
C
C H
CH2
O Methyl Vinyl Ketone
H2 -H2C C H C N H O O Mg O M O Mg O
Acetonitrile CH3CN
H3COH O
Mg O
M
O
Mg O
-H2O +CH3OH +CH3CN
-H2
Mn-MgO
OH H O
Mg O
M
O
Mg O
+ H2C
C CN H Acrylonitrile
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
H2C
CH
O-
H C
H O Mg O
N M
O
Mg O
54
6. Base catalyzed reactions
C-C Bond Formation – Knoevenagel Condensation CHO O H3C
+ Benzaldehyde
Reaction of an aldehyde or ketone with an methylene group activated by electronwithdrawing moieties
C
O
H2 C C
OC2H5
Ethyl acetoacetate
- H2O
alkali modified C alkali exchanged Y hydrotalcites CH3 C
HC
C C
O OC2H5 O
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6. Base catalyzed reactions
C-C Bond Formation – Michael Addition Nucleophilic addition of carbanions to α-β unsaturated carbonyl compounds Yield of Michael adduct (%)
100
CHT0.6 CHT1.4 CHT2.2 CHT3.0
90 80
B
Al2O3 MgO
2-(γ-oxobutyl)-2methylcyclohexane1,3-dione
2-methylcyclohexane-1,3-dione
70 60
methyl vinyl ketone
50
O
40
O H3C
30
Mg
20
+ H+
- H+
+
O
H O
O
O
O H3 C
H3C O
Al
O
O
10 0 0
4
8
12
Time (h)
16
20
solvent : CH3OH
24
Michael addition of 2-methylcyclohexane-1,3-dione to methyl vinyl ketone over calcined hydrotalcites (CHT) with Mg/Al ratios from 0.6 to 3.0, Al2O3 and MgO. Catalyst amounts used were 0.225 g for Al2O3, and MgO and the remaining weight of 0.225 g after calcination at 550 °C for the calcined hydrotalcites; T=21°C.
Mg
O
Mg
H +H O
O
OH
H3C 6-hydroxy-1,6-dimethyl2,9-dioxobicyclo[3.3.1]nonane
Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
+
-H O
O H3C
O
+
H O
O H3 C O
56
7. Acid-base bifunctional catalysis Hydrogenation of benzoic acid to benzaldehyde
HO NaOH/ZrO2
+ H2O
Sumitomo Mitsubishi Kasai ZrO2,doped with Cr2O3 350°C
Acid / base bifunctional mechanism over a zirconia catalyst (Zr4+: acid site; O2- base site) Modern Methods in Heterogeneous Catalysis Research : 18/02/2005
57
8. Summary and outlook •Fine and speciality chemicals will be manufactured in the future to a greater extent using solid acid-base catalysts •Solid acid-base bifunctional catalysis is expected to become more important in the future Problems and needs: •New bases resistant to deactivation (CO2 and water poisoning) need to be developed •Deactivation of catalysts •Development of catalysts other than acidic resins which can be used in aqueous solutuins •Universal acidity / basicity scale for solids
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Acknowledgements Thanks for data and material for illustration to Dr. Jens Deutsch, ACA Zhi-Jian Li , HU Berlin Dr. Hillary A. Prescott, HU Berlin Dr. Veronika Quaschning, BASF AG Dr. Alexander Hofmann, HU Berlin
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